New mobile shack?

Dear friends,
I was silent for a while, sorry for that... some things happened in my life (too many in fact) depriving me of the energy to follow up with things.

Said things had a huge influence on my life, thereby changing my whole attitude towards life and the future. Six years ago, I decided to no longer need a personal vehicle, hence, I sold my Merc B. The idea was to move to Canada, where I could not import my car anyway.

The plan with Canada is dead after what I have seen over the last 2 years, during which I stayed almost all my legally admitted days as a guest. Canada has changed!

Anyways, that's noch the topic here. So, After a long consideration, I got myself a personal vehicle again. And it is an EV. Fighting the idea of an REEV, the thought that such things need care for a gas engine and the attention an EV asks for, I went for battery only, skipping the gasoline part.
Long story short, with a a test drive, I decided to get a Hyundai inster. In particular for reasons of practicality. And you guessed, it was not the base model, which lacks most practical features. So, I got one with adjustable rear seats and fully foldable front seats.

The car allows for Ikea's Släkt mattress to be deployed for one person to sleep on.

The sleeping option seems sorted out for me. Now come questions about using the car as a mobile shack, as the title suggests.

With the front passenger seat folded, and the rear passenger seat in a regular position, one can create a table situation. Hyundai even sells an accessory for that... not sure if I will buy it. Looks somewhat expensive for what it is.

This car offer a so called V2L connection. Meaning, the cars accumulator (the high voltage one) and the inverters can offer 230V AC. A few 10kWh in fact. In my view, this could be very interesting when running some power amplifiers. After all, an EV is just a power-bank on wheels. In this case, a power-bank in which one can sleep.

Another use came to mind immediately, in particular with the bedding setup shown above: astrophotography. As soon as things have calmed down a bit in my life, I do see myself driving to a dark place and putting my DWARF smart-telescope on top of the car, while lounging in the rolling power-bank operating the smart-telescope from my phone.

Back to radio. An EV needs charging every so often. My intention is to come up with a shortwave setup which could be deployed quickly from the car alone. So that during charge stops, one of the other QSO can take place.
In terms of aerials I have no real plan yet. Fishing rods and PVC-pipes come to mind. My car has roof railings, however, I don't want to have anything permanently fixed. Depending on the band, a wire pyramid could be a pretty funny option (should work for 2m at least).

Fun times ahead, I hope!

60m Region 1 Crystal Combination

Sorry for having been silent for so long. There was a lot going on over the last few years.

Anyway, the present situation brought me back to Ham Radio and thinking of building stuff. However, I have to mention that this post should be considered more as a note to myself or inspiration of fellow RF designers, rather than a fully worked out recipe.

The topic of one of my next projects will be building some QRP rig for 60m. Over here in the Netherlands and in Region 1, we got a very small slot from 5351.5kHz to 5366.5kHz assigned as secondary service with a maximum EIRP of 15W. This is a range which appears to me to be almost ideal for building some QRP gear.
In modern times, we could use DDS systems to get us anywhere with anything, I must admit. In the older days, using combinations of readily available inexpensive crystals was the #1 choice for QRP.
Whilst having CW in mind, some of my thoughts my actually be useful for a side-band superhet design.

Here is what I found:

• 15.360 MHz crystals for use in a VXO (or superVXO)
• 10.000 MHz crystals and oscillators for BFO and filter stages.

To be honest, I just cooked up the idea and have not thought is through entirely. But here is what my mind came up right away.

As a side remark, subtractively mixing of crystal oscillators is a well known method of eliminating temperature drifts. So, effectively, this could lead to very stable designs, when done properly.

Transmitter

Option A is a canned 10.000MHz oscillator and push the signal through a 10MHz crystal in order to produce a sine wave.

Option B would be a regular crystal controlled discrete beat oscillator.

Mix any of option A or B with a 15.360MHz VXO to generate a 5.360MHz output signal. Should the pull be insufficient (not very likely at 15MHz) one could still use a superVXO.

Receiver

Here is where the concept presently struggles. 

Of course you would think building a crystal filter with inexpensive 10MHz crystals. However, this would probably exclude option A for the TX. Here is where the struggle lies, would it be possible to create a filter design with 10.000MHz crystals that pulls 600 or 800Hz away?

When using option B for the TX, of course, one would add a simple RIT design.

CW

You have seen me writing about two different options. Why bother, you might ask yourself. Well, to me, it is all about simplicity. 

For a mere transmitter, in option A, I might just use a canned 10.000MHz high precision oscillator and key just said oscillator, rather than a buffer stage for CW operations.  Experimentation will have to show how that sounds. In terms of simplicity, this would be pretty neat. Such a TX could be combined with some sort of SDR receiver or maybe a Polyakov direct conversion RX based on a 2.68MHz VFO.

Option B would allow for a fairly regular QRP CW transceiver. Nothing to write home about, however, this will certainly be a more complex design.

SSB

Obviously, option A is no longer available here. However, seen that it is recommended to use USB on the Region 1 assigned 30m band, it would be an obvious measure to use a pulled 10MHz BFO for both RX and TX. However, mind the mirror, we are subtractively mixing here.

Having in mind the upper portion of the 60m band, i.e. the weak signal band from 5366.0 to 5366.5kHz, option A might just come into play again. Mind you, QRSS & Co, don't mind about the sideband too much, as long as the operator knows what she/he is doing.

Over the upcoming days, I will work on a concept/prototype and hopefully will be able to report on some progress soon.

 

Finally: The PEx/Al/PEx Loop!

Yeah, that was a good one today. I took a couple of hours for tinkering and finally got to build my long planned magnetic loop aerial made from the recently discovered light weight copper substitute PEx/Al/PEx.

As previously mentioned, RG213 snug fits into the tubing material. This gave me the idea to actually slide in the coax cable in order to form a Galvanically isolated capacitor. Two reasons not wanting connect anything electrically to the aluminum: 1) it is nearly impossible to solder and 2) it will corrode in rapid rate.

As a result, the coax needs to be inserted in both open end of the loop, thereby closing the same capacitively. In principle this is like any other magnetic loop using a butterfly capacitor.
Just to remind you, this means that 2 capacitors are in series, i.e. they don't add up their capacities, they do this instead:

with Cr being the right capacitor and Cl the left capacitor.

There is a second benefit from series capacitors (in magnetic loops), they act a voltage dividers, thereby increasing the sparkling maximum voltage, allowing for higher power, in particular in the case of magnetic loop aerials.

Back to the capacitance story: the butterfly capacitor symmetrical, i.e. both capacitor have the same capacitance. What if the use variable capacitors having different capacitances?
Lets go through this with an example:
Assume that:
Cr = 10pF
Cl = 100pF
What will be the change in 1pF on either capacitor on the resulting capacitance?

• no change: (10*100)/(10+100) = 1000/110 = 9.091
• Cl lowered by 1pF: (10*99)/(10+99) = 990/109 = 9.083
• Cr lowered by 1pF: (9*100)/(9+100) = 900/109 = 8.257

Very obviously changing the higher capacitance has less influence than changing the lower capacitance.

And this is a fact I make use of in my most recent design: a magnetic loop aerial with an asymmetric series of capacitors.

Pictures say more than words:

Fig.1: asymmetric series of capacitors (purple) terminating a magnetic loop

Pic.1: real life look of the terminating capacitance

Fig.2: Dimensions used for the 20m band, blueish stuff being RG213

Pic.2: this is more than half a meter of RG213 dangling out the loop

Speaking of dimensions (finally), I need to add that the loop conductor itself is made from precisely 4m of 14x2 PEx/Al/PEx (out diameter 14mm, wall thickness 2mm).

Of course, a magnetic loop aerial needs a primary loop:

Pic.3: primary loop

Dimensions for the primary have a thumb rule: 1/6 diameter of the radiator when placed very far from objects, 1/5 in average situations and 1/4 when used in doors. Mine is made from 80cm of copper installation wire, i.e. 1/5 diameter of the radiator. Of course is very easily exchanged when going indoors.


Why are those dimensions selected?
As to the loop diameter, having a loop with a generic resonance not much above the future operating frequency allow for small capacitance values to terminate (tune) the loop. Having a low terminating capacitance lower the voltage across the capacitor and broadens the bandwidth of the loop.
The length of 4m of said material, when bent into a circle, deliver a natural resonance at about 15.5MHz. Starting from there, very little capacitance is required to resonate the loop at 14MHz.
The 70cm for the length of the "insert" were a lucky scientific a precise guestimate...

How to tune this loop and why is it asymmetric in capacitance?
Both these question seem unrelated, but they are not! The beauty of this entire design is found in asymmetry actually. Remember the section about changing the larger or smaller capacitors in a series of capacitors? The shorter end of the coax (when inserted into the tubing) acts like a "band set", the longer end like a "fine tune".
Inserting the coax entirely in a symmetrical fashion, the resonance drops to close to 9MHz, tuning here is very fiddly...
Having the coax in asymmetric configuration, the longer end provides relatively smooth tuning.

What is the bandwidth?
Well, I have not yet tested the aerial decently, but, first measurements with an MFJ-269Pro indicated that the loop, tuned to 14.060MHz is good for +/- 20kHz.
Certainly there are ways to calculate the bandwidth, the radiator 12mm has a circumference of 4m. There must be some web-application to evaluate such a loop (http://www.66pacific.com/calculators/small_tx_loop_calc.aspx) indicating a bandwidth of about 40kHz... (see below).

My plans for the loop are: QRP and PSK on 20m. Hence, I taped down the short end, as to have my band set. Of course, WSPR and QRSS are also in the reach of this loop...
This loop still is in experimental stage. For a more permanent solution, I will install an electrical box over the terminating capacitor, as to prevent water to collect within the tubing. For the same reason I may even drill a small hole into the bottom of the loop, allowing for drainage.

Concerning the dimensions of such a loop, 30m may still be an option. However, I rather see myself building this loop for the higher bands in the near future.



Results from 66pacific.com:

RESULTS:
Antenna efficiency: 68% (-1.7 dB below 100%)
Antenna bandwidth: 40.3 kHz
Tuning Capacitance: 50 pF

Capacitor voltage: 631 volts RMS
Resonant circulating current: 2.77 A
Radiation resistance: 0.223 ohms
Loss Resistance: 0.104 ohms
Inductance: 2.58 microhenrys
Inductive Reactance: 228 ohms
Quality Factor (Q): 349
Distributed capacity: 11 pF

Antenna "circumference": 4 meters

Side length: 0.500 meters

Antenna diameter: 1.2 meters

Comments:
The specified conductor length of 4 meters is OK.

Conductor length should be between 2.59 and 5.17 meters at the specified frequency of 14.06 MHz.

For highest efficiency, the conductor length for a small transmitting loop antenna should be greater than 1/8 wavelength (greater than about 2.59 meters at the specified frequency of 14.06 MHz).

To avoid self-resonance, the conductor length for a small transmitting loop antenna should be less than 1/4 wavelength (less than about 5.17 meters at the specified frequency of 14.06 MHz).

Input Values:
Length of conductor: 4 meters
Diameter of conductor: 1.2 centimeters
Frequency: 14.06 MHz
Transmitter power: 5 watts

QRP Transmatch ATU

A QRP Transmatch ATU

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Introduction

In regard of my contemporary personal situation, I decided to do something reasonable to come to new thoughts... Despite the title, this following device is not for qrp use only, as my experience soon proved. It was possible to match a 2m vertical wire at 80m with no sparks occuring up to 50W RF. But... on air experiences will show up later...

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Circuit diagram

First approach, the ultimate transmatch
 

Next try, the SPC transmatch
 

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Circuit description

For theoretical background I would like to point the reader to the common standart literature as the famous RF textbook of Meincke and Gundlach, or comparable other readings. The first approach was thought as an experiment to understand the so called ultimate transmatch (UT, first proposed by Lew McCoy). In principle I would recommend this design, also driven by my practical experience. It delivers good matching with moderate bandwidths. Besides that this design might have a slightly higher loss.
Apart from what I have written in the first version of this text, all the parts were fine to build a UT-ATU, but the rotary switch, and my attention at this time, fooled me. Thinking I got a 1x12 switch, I soldered the wires fitting this type. A few days later, reading a catalogue, it was clear, that the built in think is a 2x6 type. An additional switch cured the "problem". So, the finally completed ATU now is an UT.
Advantages: very smooth tuning even at the more critical frequencies like 29.690MHz, our local (Hamburg, Germany) repeater. QRO in this design seems not to be harmful at all, 120W RF on all available bands (40m to 10m) were matched to a 2m wire as well as to a 10m wire w/o sparkling ATU ;-)
As a comparison, I chose the series-parallel capacitance transmatch (SPC), for the reason that it took me just two leads reconfigured to convert on to another. Formerly I also planned to test the standart transmatch, but the overwhelming wish to get on air forced me to stay at the simple - to - obtain - by - the - most - simple - modification - design (smiley!). Disadvantages in this design (agn, have a glance to the textbooks) are the extreme narrow bandwidths and the low QRO ability (high Q).
What to chose if money plays no role? Certainly I would go for the UT, with two two-gang vernier capacitors at 1nF max (in both sections) and a roller inductor... if... but... it's all built from the junk-box.

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Parts descriptions

The capacitors are the simple part. I just found them on the bottom of my junk box. They look like they were intended to go into AM broadcast receivers. In either design one has both sections wired in parallel. The inductor, the tricky thing in matching units with variable inductance. For the body I found an old pill container with a diameter of 4cm. The coil is then wound on this with 60 windings of 1mm enameled copper wire. The first 36 windings tight together, the rest with increasing wire to wire distances to the upper (hot) end of the coil. Tabbings are located at the windings 19, 28, 37, 42, 47, 50, 53, 55, 57, 58 and 59 for use with a 12 positions rotary switch shortening to ground, as I thought... In reality it's a 2x6 with an additional switch.

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SWR indicator

My good friend Rico (DF2CK) had the heart to donate a PCB reflectometer to me. To make one yourself, have a look at Harry's (SM0VPO) Homebrew Page. Can't remember the way Harry did the rest, I added a 47k potentiometer for sensitivity adjustment, and a 4k7 suppression resistor to the forward meter, for reasonable reading during the tuning process. The meter itself is a standart stereo VU-meter, found in obsolete tape recorders (other superb parts could be found there likewise). Usage: Highest sensitivity and lowest reasonable RF power to start with. During the tuning you certainly will increase the RF power the closer you are to good matching. With CW, your favoured mode ;-), you then automaticaly will have the correct sensitivity setting during QSOs. For SSB contacts, you should keep in mind to reduce the sensitivity close to zero after tuning. The clicking meters will remember you to do so elsewise. Weak nerves would make you think of a sparkling capacitor, hi!

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Tuning procedure

Yes, I know, that's common knowledge... but... we have two designs in this report. My experience was that the both designs have a contrary behaviour. Tuning with the UT: Fiddle during RX with all the buttons to get the loudest noise. You're allready close! Next is done with a little RF applied, power depending on the band, little fine tuning, done! QSO! Tuning mainly was done during RX. On the other hand I experienced that the RX maximum must not be the minimum in SWR.
Tuning with the SPC transmatch: More difficult, because of the narrow bandwidths. Set your transmitter to a few tens of milliwatts to find a C-L-C combination where the reflected power is halfways acceptable. Now the game begins! By slightly in/de-creasing certain capacities and inductivities find a good match. You will notice, it's much more complicated to find a good match, as the SPC transmatch with the given parts will provide exactly one for a specific aerial<->QRG combination.

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Experiences

Clearly the SPC transmatch easily is able to match a 2m wire to 3.5Mhz w/o any problem, but, whatever band you're QRV on, watch the reflected power... Using the SPC transmatch, you will have to retune every tens of kHz. The UT give, as mentioned above, broader bandwidths. With both designs it now is possible to match a 2m wire to all bands (even 160m, although this makes no sense at all). It was easy to confirm the statements given in the literature about the behaviour of the presented matching networks. So, before you start soldering, think about what kind of aerial you want to match, and have a closer look to the textbooks. The opinion given there is that the UT can better handle inductive loads while the SPC transmatch is performing smoother on capacitive loads.

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Photographs

The inductor. I know, does not look extremely professional...

Box, partially assembled. The capacitors are glued to PVC insulators (using hotglue). Also the pill container inductor is glued to the box. On the left side, you can see the reflectometer PCB.

Box, completed. The knobs for the capacitors nowadays are replaced by larger ones, depending on the settings your hand has a strong influence to the capacities.

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Half-wave 27MHz Antenna as Broadband Vertical

Years and years ago, a friend of mine gave me a (brand new) half-wave CB antenna. Well, I have never used it, for the reason of not being QRV on 11m. For 10m I had my double bazooka, so there was no need for it. Now that it has been sitting in a corner for a while, I thought, maybe it could be useful for something else. Some else as in broadband vertical...

Now, let's have a look how those things are built:

aerial schematics

This drawing is not made by me, however, it nicely sketches what the following photographs of my very own version of that antenna show.

all still in one part

taken apart

What we have is the cavity and the transformer that was sitting in it. The air core transformer has got a winding ratio of 7.5:2. I figure, using a ferrite or iron powder toroid would improve performance on lower frequencies.
The cavity measures 35mm in diameter, having a depth of 24mm. This clearly offers enough space to house a smaller toroid transformer.

At this place, I would like to remind you of the BB7V (Diamond) having an UnUn transformer with (resistive) termination shunt. This vertical would be 6.7m tall. The regular 11m half-wave vertical could possibly be stretched to a tallness somewhat beyond 5.5m. Close enough to me.

Now let's think... for QRP work a T80-2 would make an ok UnUn. With some luck, transformers with a T130-2 core could possibly be squeezed in the cavity, if made carefully.
Reconsidering the BB7V's terminator, would I put one in there? Only if I would be using this aerial for QRPp only. The base of the CB-aerial is made from plastics material, which is not able to conduct any heat. Hence, heat created inside the cavity would never be dissipated. For QRSs/QRPp, the resistive terminator is a very appealing option, in particular since for such power levels, a T50-2 transformer would offer sufficient empty space for the terminator.
A T130-2 would possibly be good for a regular 100W rig. However, in a worst case, 50W of heat have to be dissipated, hence, some cooling of the termination would be required, therefore, this is a no-go. Some adjustments and selective use of bands would still be an option for such an arrangement.
Personally, I am very tempted to try a version of a T68-2 transformer (not sure about termination yet), in combination with my IC-703. This is somewhat of a compromise...
Should I ever again get into QRPp/QRSs/WSPR/WSJT/ROS actively, my preference would be the small transformer&terminator option.

Additionally, I figure, it could be of use to add an additional Al-pipe of about one meter to the top of the vertical. This will result in a total length of about 6.4m and a further distance to a quarter-wave on 20m, without getting too close to a quarter-wave on 30m.

There you have it, a new life for a cheap half-wave 11m vertical.

Look What I Found!

A local hardware store offered those:

F2BNC

F Type Connector to Bayonet Nay Connector adaptor. Those essentially conclude my usage of overpriced 50Ohms stuff for QRP applications.
Well, the adaptors did not came cheap, they are €2.40/pc, but I feel they are totally worth it.

Skanti Marinetta TRP 1

I got lucky! Ever since I made my GMDSS-GOC, I wanted one of those:

Skanti Marinetta TRP 1 portable survival radio

In the Scheepvaart en Transport College Rotterdam, where I studied for the GMDSS-GOC, those units are on display. You can only guess how happy I am to finally got one into my collection of marine radios. The best thing on this purchase, the set is complete with all standard accessories.
I would like to thank Willy PA0WMR for keeping this rig in near original state. Willy also stated that the transmitter delivers about 5W on 600m.

What is all the fuss about a yellow box anyways you may ask. And the question is well justified. First of all, the box, with the lid closed, swims ;-) It is yellow! (That would be a reference to Douglas Adam's Hitchhiker's Guide to the Galaxy).

OK, lets be serious, why am I so happy to finally posses one?
Having a look at the manual/schematics we see that the rig

• has a modern (digital) design
• operates on 500kHz, 2182kHz and 8364kHz
• is crystal controlled
• allows for CW and AM
• has a built in dummy load
• employs an antenna current meter
• contains an ATU
• can create its own energy (by means of cranks)
• can be energized by an external source

500kHz, 2182kHz and 8364kHz are (former) distress frequencies and must not be use by ham- radio operators! 

Where is the hamradio use of these units? Well, we all hope for the 600m band. The 500kHz signal is created by a  2.000MHz gate-XO and digital dividers. Depending on what band we will finally get, this crystal can simply be replaced by a fitting one. However, since it is a digital XO, on simply could remove the crystal and feed a DDS generated signal into the digital gates.

According to the schematics, the transmitter's 8364kHz crystal can easily be replaced by a 40m crystal. However, the receiver employs some resonant LC-stuff with varactor tuning, which should not pose a major problem to modify to 40m, e.g. 7030kHz.

The receiver uses a 2682kHz crystal oscillator to the 2182kHz emergency frequency. The transmitter employs a 2182kHz digital gate oscillator. We got two options for ham-bands here, 160m or 80m. Both have pros and cons. 2182kHz originally is an A3 frequency. The wiring inside the TRP 1 is providing AM modulation accordingly.
On the 80m band, AM is used in places, hence, that would be a nice possibility to join the action. However, filters will have to be modified.
On the 160m band one may want to aim for A1 operation. A 1.843MHz crystal would do the trick here... However, the wiring will have to be changed to engage the BFO in the "2182kHz" labeled switch position.

What is the prospect for the future use of the rig?
I believe it would provide endless fun during field day operations. In particular when operated from cranks, independently from any power supplies.
The (yellow) box contains everything needed for QRP-ops, including a telescopic vertical antenna and a "long(er) wire" aerial.

I figure it could be reasonable to replace the TBA570 receiver with a NE612 superhet design for side-band use.
The XOs could be replaced by either a DDS or some synthesizers for enhanced flexibility.
Some PIC controls seem obvious, the automatic SOS-TXing is inadequate, obviously.

It all comes down to how much modification is actually wanted. Maybe the greatest fun can be obtained when staying as close as possible to the original functionality, i.e. AM on 80m, CW on 40m and 600m.

Other than that, it is an extremely nice addition to my marine radio collection.

17m XTAL Controlled QRSS / WSPR / QRP / SDR

Sorry for having been silent for a while. Some new thought, although not entirely mine, I believe sharing it this way would be more than appropriate.
The idea about the frequency generation is borrowed from DJ1ZB. Ha-Jo uses CB crystals on their fundamental and doubles the result.

Doubling sounds very much like two things I previously disclosed on this blot, namely, the subharmonic direct conversion receiver (e.g. this) and the subharmonic I/Q-SDR (see earlier posts on the SDR and possible frequencies).
Both designs rely on a local oscillator on half the operating frequency.

Concentrating what could be interesting for QRP, QRSS and WSPR, lets have a closer look to the available crystals.

• 27.105MHz (12T) => 9.035MHz x 2 = 18.070MHz
• 27.135MHz (15T) => 9.045MHz x 2 = 18.090MHz
• 27.155MHz (16T) => 9.051667MHz x 2 = 18.103333MHz
• 27.165MHz (17T) => 9.055MHz x 2 = 18.110MHz

The frequency generated with a 15T-XTAL appears to be ideal for I/Q-SDR since the whole CW & Data & beacons range will be covered by 48kHz sampling rate. Have a look: difference 18.090-0.024=18.066 and sum 18.090+0.024=18.114.
Additionally, 18.090MHz is the quite close to the QRP frequency, a subharmonic direct conversion receiver would be an obvious choice, so would be a transmitter with a doubler...

Very obviously, the other frequencies are directed more to QRSS and WSPR. I am not going into the QRSS feature here, it is kinda trivial (see above).

Remaining topic: WSPR. The frequency produced by the 16T-XTAL is very very close to the WSPR "dial frequency" 18.1046MHz. With a Pierce oscillator the tiny amount of 633Hz upwards pull should not be a big deal; remember, on half the frequency, one only needs to pull half the distance.
RX: subharmonic direct conversion.
TX: subharmonic mixing of the local oscillator with an audio signal should create a DSB signal... that's the theory... I have not yet tried it yet, however, I fail to see any reason why this should not work.

NIKKEI NRB10 or a Retro QRP Enclosure

I should not be left alone in electronics stores, I guess. The temptation of buying one of these was just to great, even if the price of about €20 is not really calling bargain.

Here what the receiver looks alike

NIKKEI NRB10ZT

I figure, the ideal front configuration for a multi-band CW QRP station. Looks cool too! The switch on the right-hand side has got 4 positions: OFF - FM - AM - AUX. Some ideas for that switch:

• OFF - 80m - 40m - 20m (multi-band CW transceiver)
  
• OFF - AM - LSB - CW (75/80m single band multimode transceiver)
• OFF - RX - TX - TUNE (75/80m AM transceiver)
• OFF - 2.7kHz - 1kHz - 500Hz (single band CW-TRX w/ several filters)

The left-hand volume potentiometer would very likely keep its function.

Nice bit on the kit, the main tuning knob is equipped with a vernier drive!

The red and green LEDs could serve all sorts of purposes... and also the scale back light could be used for something.

What about the back side of the radio? Again, perfect for QRP! Have a look:

NRB10 back cover

First of all, the material of the back cover seems good workable soft plastics. More interestingly however, enough sockets for all sorts of things. Some thoughts:

• keep the RCA for the speaker, since this is already done
• use the mains power cord to connect to the 12V station supply
• replace the 75Ohm socket by a 50Ohm BNC socket
• headphones will remain as is, it is nice to have the correct symbol printed on the cover
• REC OUT also could be used as such, for connecting the rig to a computer
• AUX will serve as a KEY in or a MIC/PTT

I can't wait to have that box operable, sitting on my living room table. Hmmm, probably, I should write less and solder more ;-)

SmallWonder Labs PSK-20 QRSS/WSPR mod

Some time ago I built a PSK-20. Even though PSK31 can be fun occasionally,I was thinking of added value to the radio.

The radio uses an intermediate frequency of 9MHz, which is mixed with a 5.0688MHz "computer" crystal oscillator.

I see two possibilities:

1. • Make the 5.0688MHz crystal replaceable with a 5.000MHz crystal. This mod will get you to the 20m QRSS band at 14.000800MHz and the radio will still be usable for PSK31.
   • There is no WSPR in this mod? Yes, there is, it would be all about penning down a 5.120MHz crystal to 5.0956MHz, which is quite a stretch but doable.
   • Some additional frequencies in the upper digi-mode band (14.101-14.112MHz) are reachable in a similar way.
   • Finally, there is a 5.200MHz crystal, which would make up to a perfect single channel SSB DXpedition transceiver. I guess one needs to look at the IF-filter response in this one.
2. • Change the intermediate frequency to 10MHz and the local oscillator to 4.000MHz.
   • PSK31 operation will be gone, since there is no (cheap) crystal for 4.070MHz. OK, the last statement is not entirely true, one could pen down a 4.096MHz crystal to 4.069MHz, although, 27kHz is a lot.
   • But, WSPR is on the easy side by using a 4.096MHz xtal in the LO.
   • Additionally, one SSB channel is available with the LO running at 4.194MHz; I guess one needs to look at the IF-filter response in this one. 14.194MHz would be ideal for SSB DXpeditions.

Please not, one needs to make sure that the BFO is set for USB!

Actually, I may start with option #1, to keep the original functionality.

The HC-8 CW QRP Transceiver

I got something on my mind, which is probably not too hard to design, and could be a nice trx to take along on journeys: a modern days clone of the HW-8.
The design will entirely be based on 74HC digital electronics, hence the name HC-8.
It will employ a 8.867MHz super-VXO. Reason for this being the HW-8 itself (find out more about this in an earlier post).

The CW portions of 160, 80, 40, 20 and 17 can easily be covered by such a super-VXO in combination with some cheap crystals. 30 required some more efforts. For good measures, I will include the already shown list:

• 160m: 8.867 - 7.000 = 1.867
• 80m: 8.867 - 12.406 = (-) 3.539
• 40m: 8.867 - 1.843 = 7.024
• 20m: 8.867 + 5.185 = 14.052
• 17m: 8.867 + 9.216 = 18.083
  

As mentioned above, the plan is to use digital gates as much a possible.
This would be possible solutions:

• 74HC00 - oscillators, drivers, AF-amp
• 74HC04 - oscillators, drivers, AF-amp
• 74HC86 - oscillators, drivers, mixers
• 74HC4066 - oscillators, mixers, signal routing, class E "driver"
• 74HC240 - driver, PA, AF-amp

Practical Considerations

With the 74HC240 running from 8V (upper limit for this particular chip) one could imagine to drive a class-E switch-mode PA (IRF510) that easily would produce 5W RF.

The HC-8 wont be providing any IF filtering. I intend to go for pure direct conversion, (super) VXO on 8.867Mc and r.i.t. on the respective other oscillators. I have not yet figured out how to do this the best
way.

Switching low pass filters in a multi-band transceiver can pose a problem, therefore I am envisaging to go for 2 bands only (switches are available, small and not too expensive), but build two rigs:

• 80/40 for NVIS
• 20/17 for DX

One could consider one trx for 40/20 to get the best of two worlds.


Added Value
 
You're missing 30m? OK, here is 30m, it's a tricky one however, in particular for filtering! Frequency division would be available using 74HC74 Flip-Flops. Signal source: a 5.0MHz xtal or a not so common 38.0MHz oscillator.

• 8.867 + (5.000/4) = 8.867 + 1.25 = 10.117
• 8.867 - (38.000/2) = 8.867 - 19.000 = (-) 10.133

Even long-wave would would be available (although such a rig would maybe not that practical for such low frequencies):

• 8.867 - 9.000 = (-) 0.133

Note: For some bands the VXO is required to oscillate above 8.867MHz. Some thought should be invested when designing the VXO. Maybe for the reason of frequency coverage, the VXO should involve discrete transistors in place of digital gates.


As antenna to go along with the rig I see the RockLoop as best fitting. Very narrow-band antennae have the advantage of good harmonics suppression. Alternatively a high-Q transmatch should be used for the same reason.

HB-1A now Ten-Tec R4030 & R4020

Interesting... the HB-1A QRP-transceiver, made by BD4RG, which disappeared from ebay where it was sold for a while reappeared at Ten-Tec's product range as R4030 and R4020. The manual, download-able from Ten-Tec, even shows "HB-1A 3 Band CW QRP Transceiver".

Funny, the original 3 band TRX is now available as 2 different 2 band TRXs. I wonder why this limitation, which most likely is just a bit of code in the main controller, was added. In particular since the DDS still is mentioned to deliver a receive range from 5-16MHz, as in the original HB-1A. Looking at the schematics, the only reason that I can see is the switchable low-pass filter. Probably some FCC requirements about spurious transmissions. I have doubts about commercial reasons; who would by two transceivers being more or less the same. When going on a trip, the three bands 40, 30 and 20 seem ideal. Now the OM has to select, either the band that is open around the clock, or the band that delivers the best dx results in average.
For myself, if I would consider trying to get my hand on a radio like this, I would go for the original HB-1A. Harmonics suppression in my travel kit is done by the aerial, which usually is a very narrow-band "rockloop".

When it all comes to buying, I would very likely go for the real original, the Elecraft KX1, which nowadays covers all band from 80 to 20.

UPDATE: Today, 10.11.2010, I decided to order a Hendricks PFR-3 kit. The design is thought through and straight forward. The controller however allows only for 40, 30 or 20m HAM-band action, no BC-RX though. In my view, this is a tiny downer...
The PFR-3 transceiver carries a built-in manual transmatch and a preselector, which sounds "old skool"... and it is! And that is why I ordered the kit.

2030kHz XTAL

Browsing one of the regional electronic (online) shops, I found a 2030kHz crystal, which would be perfect for a couple of projects. The order seems a little odd, however, the order reflects the difficulty of the different projects, the further down, the more difficult to realize.

600m I/Q-SDR
For the typical SDR, one could simply feed this signal into two Flip Flops, resulting in an SDR LO of 507.5kHz.
With a minimum sampling rate of 24kbps, a range from 495.5kHz to 519.5kHz would be covered. This is in particular interesting since 518kHz, the international NAVTEX frequency falls into this range.

2200m I/Q-SDR
Taking one of the two 507.5kHz signal and feed it into two further Flip Flops would provide an SDR-LO of 126.875kHz, which would provide a frequency range of 114.875kHz to 138.875kHz, covering the 136kHz amateur radio band.

40m QRP Superhet
As non SDR use of the crystal, a more classical approach is in reach: a 2030kHz (super-)VXO and a 5000kHz crystal filter coincides nicely with the 40m QRP frequency. The 2030kHz crystal could additionally penned down (see earlier post about xtal-penning) to cover lower frequencies in the 40m CW section.

20m QRP Superhet
Also the 20m QRP frequency is easily covered. The trick here, a 2030kHz (super-)VXO as LO for a subharmonic mixer, which per se doubles the LO-frequency. Hence, the effective LO-frequency would be 4060kHz. In such a concept, it would be somewhat obvious to use a 10MHz crystal filter.

10m QRP Superhet
Similar to the 20m concept, a subharmonic mixer would be required. As intermediate frequency, 24.000MHz would be obvious. However, watch out for the correct crystals for the filter! Most crystal will be overtone crystals, for a cheap filter we would need fundamental frequency crystals, and yes, they do exist for 24.000MHz.


40m LSB Superhet
Here is a simple one. The sum of 2030kHz and 5068.8kHz results in 7098.8kHz. I would propose to build a full-lattice filter with two original and two penned down 2030kHz crystals. As LO a super-VXO using 5068.8kHz crystals would an obvious choice. Additional options would be a 5120kHz VXO (getting us to 7150kHz), a 9216kHz VXO (9216-2030=7186), or, for some of us, a 5200kHz VXO (7230kHz).


80m LSB Superhet
This could be a tricky one. I would, once again, propose to build a full-lattice filter with two original and two penned down 2030kHz crystals. A conceivable could employ a 5.74MHz ceramic resonator. Subtractive mixing would provide a range, depending how far one pulls the VFO, of a couple of 10kHz about 3710kHz.


There may be more uses of this crystal, feel free to add comments with additional ideas!

Ramsey QRP80C considerations

My first awareness of that kit was in 1995, when there was a German supplier for this sort of stuff. I looked at it, and since is was a long way from being spectacular, I forgot about it again. Until recently the search for QRSSable kits started. The manual, which contains all vital information, besides the schematics diagram, can be downloaded from Ramsey electrics' webpage. With all parts listed, block and layout diagrams, it is no problem at all to reverse engineer the schematics; which I did. For reasons of copyrights I will not publish the result however.

As I said, the kit is not really spectacular, that what my understanding of the circuit is:

• Colpitts xtal oscillator (2N3904)
• common emitter buffer (2N3053)
• class C power amplifier (2N3053)
• crystal pulled by two varactor diodes
• comes with color burst crystal (3.579545MHz)

In the manual it reads that the oscillator can be pulled 7kHz about the nominal frequency. For 80m I feel that is somewhat ambitious, but can't tell until I have built the kit (just ordered).

There is a switch that toggles between two crystal positions.

Now let's see what can/should be changed:

1. There is a jumper JMP1 which supplies the tuning potentiometer R1 with 12V. I my view this jumper must be replaced by a voltage stabilizer, such as a 78L08. OK, will provide a little less pull, but should be much more stable.
2. The oscillator is keyed, OK-ish for QRP, not acceptable for QRSS. Here there are a couple of options, supply the oscillator from the voltage stabilizer and key the PA instead (heavier keying transistor required!), key the buffer only or used FSK only.
   Running the oscillator from the stabilizer:
   Cut the PCB between R5 and R7, run a wire from R1 (tuning pot.) hot end to R7.
   For keying the buffer, nothing will change, since the base of the buffer is pulled up by the keying voltage via R8. If the load change on the oscillator is not too great, this should not be creating too much chirp (to be tested!).
3. Add some resistor/transistor/what not stuff to supply a tiny bit of FSK voltage to the point where R1, R2 and C1 are joint.
4. A second crystal could be 3.500MHz or, as soon as there is one, 3.600MHz.
5. For QRP, the place for the second crystal could be populated with a 3.58MHz ceramic oscillator which will have a much wider pulling range. With a chance of 99.9% I will do this! So there will be one QRSS and one QRP mode for this transmitter.
6. Also for QRP, two identical crystals could be installed in parallel, this would be a so called "superVXO". The PCB offers sufficient space so that two crystals could easily be installed where only one was once planned.
7. When no receiver is going to be attached to J2, or RX/TX-toggle is done externally, J2 could serve as an input for the FSK keying. In this case the diode D1 can be replaced by a jumper. The parts L5, R11, L4, D2, R12, R13 and C19 must/can be omitted when D1 is replaced by a jumper.
   I consider that a keying circuit can be build in place of the RX/TX-switching stuff:
   The place of C19 could be used for a 10k resistor connected to the base of a NPN transistor (somewhere close to the tuning pot.). Said transistor could influence in one way or the other the tuning voltage....
8. The resistor R9, which feeds the buffer, should be increased in order to not overheat the PA transistor in a 100% duty cycle. A trimmer could be added in series to R9 to allow for variable output power.
   Alternatively, a resistor could be wired in series with the choke L3 which feeds the PA transistor.

Those are the mods that came to my mind. There may be more....

Another more general idea: When looking at the parts layout diagram, two pulling inductors are foreseen for the 80m version. For less pull, one could certainly omit one by shorting it (temporarily?), which will allow smoother tuning for QRSS.

Looking forward to receiving the kit!

The ClockMite Transceiver

As the name suggests, this design follows the basic ideas of the RockMite transceiver. It will be, however, more digital...
First ideas are the following. The bag of components will be containing the following

1. one oscillator for 5.0680MHz
2. one oscillator for 5.0688MHz
3. RA3AAE mixer for RX
4. one XOR-doubler for TX
5. 74HC4066 switch
   
6. 12F629 controller
   

The doubler and the mixer will ensure operating frequencies of 10.1360MHz and 10.1376MHz, which represents a difference of 1.6kHz (surprise surprise). A 1.6kHz tone is not really pleasant to listen to, I agree, but the simplicity of this transceiver will make up for it.

Both oscillators will be on at all times. Both oscillators are routed (74HC4066) to the active doubler which by default is switched off.

TX: The doubler is switched on only when the transmitter is keyed. The controller will route an oscillator to the doubler and activate the same.

RX: One oscillator is routed to the mixer, preferably via a 5.0688 crystal.

The controller will include a iambic keyer but will also allow for straight keying. A further task of the controller is to toggle between the high and low frequencies.

Green Radio

A long time ago, I spent a little money and got myself a GRC9. Yep, green radio. That was to a time where you got whole sets and not just the main event. It came with all aerials, spare parts, headphones, microphone, morse key, speaker, power amplifier (LV80), inverters, two rucksacks full of stuff, all cables, service manuals, etc... It still sits in Freiburg and is waiting for me to pick it up.

Meanwhile, I decided it was time to obtain a SEM 35. In contrast to the GRC9 it came naked. Yep, it really did. Just the transceiver and the clipon power supply - no handset, no aerial, no power cable and worst of all, no circuit diagram.
Took me about four full evenings on the internet to finally locate eight image files on the circuit diagram. Ohhh boy!!! Now, I ordered a handset, speakers seem to be unavailable. Let's hope for the best!

It was claimed the SEM 35 was comparably stable, even with the PLL disabled (there is a mod on the internet that allows for continues tuning of the rig telling so).
Here come in options for modifications, i.e. expanded usability...
The rig has got a first i.f. of 11.5MHz and a second i.f. of 470kHz. One could considered doing something with that. Something like adding an SDR to the intermediate frequencies. This would give a range of about +/- 48kHz (96k-sampling rate) about the center of a channel. With a channel spacing of 50kHz, the whole range is covered with nice overlap.
For the first i.f. options are a 46.0MHz oscillator for the normal approach and 15.333MHz for the "softrock lite 30" approach. Honestly, since there are no crystals, one need to think of a more advanced solution.
The second i.f. could be dealt with using a 1.880MHz oscillator, which to me again looks like a more advanced thing to do. But there is an offset solution: 1.8432MHz, resulting in a center SDR frequency of 460.8kHz. Actually, I do prefer this, for various reasons.
The plan is, as soon as I got my act together, to add an SDR receiver, maybe a softrock, in front of the 470kHz i.f.-filter.
I am curious if the stability of this green radio from the seventies is good enough to capture 10m WSPR and QRSs.

If the above project is successfull, one could consider of doing something similar to the transmit train, allowing for CW. The PA of the SEM 35 looks linear to me, which, in a pure FM rig, does not make much sense however. Before running sideband through it, some more thinking and testing is required.

SW PSK-20 upgrade ideas

Lets face it, I cannot help it and have to think of alternative uses regularly.
QSOing on 20m in PSK31 is fun. However, I think there are more options for the PSK-20.

The first thing that came to my mind, adding some switchable local oscillators. The design of the PSK-20 is a 9.0MHz i.f. with a 5.07 l.o. (5.0688MHz crystal). Here comes the idea, one could add some voice channels using cheap crystals:

• 14.120 = 9.0 + 5.120
• 14.185 = 9.0 + 5.185
• 14.200 = 9.0 + 5.200

Or, with oscillators divided by two:

• 14.120 = 9.0 + (10.240 / 2)
• 14.350 = 9.0 + (10.700 / 2)

Using (external) oscillators, one may consider using superVXOs for increased coverage.
This however would require to run a microphone preamp with an active low pass filter. The crystal filter of the PSK-20, for obvious reasons, is wider than a sideband filter.

The second idea is focused on the fact that the intermediate frequency is 9.0MHz.
As you may have seen, I was experimenting with a softrock lite on 30m. Those experiments where mainly aimed at the usablility of the softrock lite for 30m QRSS reception.
The softrock uses super-Nyquist, in short, the center frequency is 0.75 times the l.o.-frequency. This makes it comparably easy to use the softrock lite to "look" at a 9.0MHz i.f. with a l.o. crystal of 12.0MHz. This would add SDR and panoramic display to the PSK-20.
But, not only, since there also is a crystal 5.0MHz (or 10.0MHz divided by two):

• 14.000 = 9.0 + 5.0

Reception of the better part of the CW band and the QRSS region at the lower band edge would be possible. For QRSS reception it would be advisble to pull the 12.0 MHz softrock l.o. down.

And finally, one could think of penning down a 5,0688MHz crystal, in order to reach the QRP frequency. All one would need for a CW qso would be a 800Hz sine generator.

3 Band CW QRP TRX

Whilst I was looking at crystal frequencies for the new qrss-ranges, I came along a very nice combi for a 3 band qrp trx for the bands 80m, 20m and 15m. (Frequencies in MHz)

• 3,560 = 11,0592 - (15,000/2)
• 14,060 = 11,0592 + (6,000/2)
• 21,060 = 11,0592 + (20,000/2)

The division will be done by a flip-flop.

The combination offers the option for a ladder filter at 11,0592. In this case, one could consider, as an experiment at least, a subharmonic b.f.o. using a 5,5MHz ceramic oscillator in combination with a RA3AAE-mixer.

Writing of ceramic resonators, there is one for 6,0MHz. This would enable a nice v.f.o.-range for the 20m band.

When crystals are to be used, one could consider using a super-vxo.

UPDATE: Jan came up with an idea of adding 40m by using the combination

• 7,037 = 18,096 - 11,059

OK, 7kHz is quite a stretch to pull, possible however, TNX Jan!