Monday, January 31, 2011


This could be a fun one to do: dual band NVIS QRSS.

Not sure what NVIS is? Please have a "google" to find out. There is a lot of excellent documentation available.
The only bit of info about NVIS I would like to point out in the post would be the fact that the 40m band is good during the average day and the 80m band is good for the average night. Running both in parallel could show some interesting daytime nighttime transitions.

Due to the harmonic nature of the 80m and 40m bands the easiest approach for a transmitter design would be to build an oscillator for either band and generate the other frequency by division or doubling. The downside here: shifts and offsets would also be divided or doubled.

A receiver also could make use of a single local oscillator. Here the most simple design would be a regular direct conversion mixer for 80m and a subharmonic direct conversion mixer for 40m. The respective audio frequencies could be fed into one single stereo sound card using left and right channels.

Frequency-wise, there are two obvious possibilities.  Both have pros and cons:
  1. 3500400Hz & 7000800Hz
  2. 3579545Hz & 7159090Hz
The first option will make this sort of QRSS activity visible in grabbers as presently operated, it is however, due to the price of the crsytals more expensive than the second option.
The second option uses frequencies for which very inexpensive crystals are available, the big pro on the second option would be that is will enable many more hams to operate a transmitter legally (the ole novice story).

By now, you may have asked yourself why crystals still play a role here. Well, not so much for the transmitter, although they make nice filters for oscillators using digital gates. For a possible receiver those crystals would make ideal narrow front-end side-band filters, which are in particular important when operating in the middle of a busy band.

Want something more complicated?
What about a "superhet" design? With center (intermediate) frequency of 5.250800MHz and a 1.750MHz local oscillator the mixing products would be 3500800Hz and 7000800Hz. When shifting the intermediate frequency, both the 80m and the 40m frequencies will shift by the equal amount in the same direction, that's kinda cool!
Now to the tricky business how frequencies could be generated. Lets start with the easy one. 1.75MHz is subharmonic to 3.5, 7.0 and 14.0MHz. The first two call for trouble since those are too close to the final operating frequencies (*). But what about 14.0MHz? Crystals and even oscillators are available for this one! A division by 8 (ripple counter) will result in a very stable 1.75MHz local oscillator.
And here is the challenge: 5.250800MHz. There is a crystal for 5200kHz, but a 50kHz pull is too much and grinding is a tricky business. There may be a 10.5MHz crystal available, somewhere... As a last resort, a DDS would possibly do a superb job. This however would also be the most expensive solution.
(*) Problem for the TX, solution for the RX, subharmonic to 80 and 40 and the same time!

Want something even more complicated? No problem! That one is so overcomplicated, that is should rather be seen as experiment in thought. What about SDR? Take a 10m QRP crystal (28.060MHz). This frequency is perfect for a 40m SDR, center frequency: 7.015MHz. A quadrature local oscillator can be derive by a division by 2, resulting in a 14.030MHz local frequency and a 3.5075MHz SDR center frequency. For reception, 2 stereo channels are needed and to provide I and Q for both bands. TX in such a case could be done by either individual audio frequency generators w/ 90 phase shift networks or in a way similar to the LO, with a 56.9kHz generator.
As I said, the SDR is somewhat hypothetical, not practical in any way....

The superhet TX design presently appears to be favorable, together with a subharmonic direct conversion receiver for 80 (1.75x2) and 40 (1.75x4).

Friday, January 28, 2011

4MHz - the Magic QRSS I.F.

Although the QRSS-community seems not to be as technical as it used to be, some thoughts about the matter from my side.

Some OM, again I am writing about novice/foundation/newcomer-lis, may not be allowed the lower band edge. But still, most activity takes place at those spots.

I asked myself, if I could find crystals to suite both needs. You will find some combis for one or the other option on this blog.

Meanwhile, I believe that 4.000MHz is the ideal I.F. for QRSS. Here's what can be done (more or less easily):

600m 4.5025MHz-4.000MHz=(27.015/6)MHz-4.000MHz=502.5kHz
The trick here, use a CB transmit (overtone) crystal for 27.015MHz (5T) and operate it a its fundamental, i.e. 9.005MHz. A division by 2 (flip flop) will end up at 4.5025MHz. A VXO at 9MHz may be pullable by a few kHz, hence, we may be able to cover a substantial portion of the present 600m hamradio band.
Should a future allocation be somewhat higher, there are many other CB-TX-XTALS available.
Should a future allocation be somewhat lower, there are many CB-RX-XTALS available.

NAVTEX 4.5175MHz-4.000MHz=(27.105/6)MHz-4.000MHz=517.5kHz
Essentially the same as above... the crystal being a 12T. For those who are not aware, there is maritime navigational (and weather) information transmitted on 600m, to be precise, 518kHz (international frequency) in FEC.
NAVTEX also knows a local frequency, which is 490kHz. This frequency is reached with a 39R (26.940MHz) xtal.

80m 4.000MHz-500kHz=3.500Mhz
500kHz can easily be generated from a 4MHz signal by dividing the latter by 8 (ripple counter). Running a 4MHz Pierce oscillator, the generated frequency will be above the 4MHz series frequency. Assume we generated a frequency of 4001kHz, 1/8 would be 500.125kHz, resulting in a mixed QRG of 3500.875kHz (TX).
For RX, a tweaked (fine tuned) L.O. can be used as B.F.O. to provide a reasonable beat for reception.

40m 4.000MHz+3.000MHz=7.000MHz
That would be the lower band edge solution... further comments here... however, there are better options!

40m 11.000MHz-4.000MHz=7.000MHz
Again the lower band edge, however, this is subtractive, therefore, temperature drifts will not add up but rather cancel (or at least reduce another).

40m 11.059MHz-4.000MHz=7.059MHz
This QRG is open to novice/foundation/newcomer-license holders! Temperature drifts will not add up but rather cancel (or at least reduce another). The frequency is at the upper edge of the 40m data segment, I believe, it is an ideal playground for testing all sorts of modes.

30m 4.000MHz+6.144MHz=10.144MHz
The classical 30m QRSS frequency is in close range. A local oscillator will have to generate a frequency of 6.139Mhz, which is reachable by either pulling of penning of a 6.144MHz standard crystal.

20m 4.000MHz+10.000MHz=14.000MHz
This is a no-brain-er! Just run a 10.0MHz LO.

20m 18.000MHz-4.000MHz=14.000MHz
This is a no-brain-er having improved temperature behavior... subtractive...

17m 4.000MHz+14.080MHz=4.000MHz+2x7.040MHz=18.080MHz
Here, the local oscillator would be sub-harmonic. 7.040MHz is just one example of many possibilities opened by crystals available for the 40m ham-radio band.

15m 25.000MHz-4.000MHz=21.000MHz
This again is a no-brain-er having improved temperature behavior... subtractive...

10m 4.000MHz+24.000MHz=28.000MHz
This is a no-brain-er...

10m 4.000MHz+24.000MHz=4.000MHz+2x12.000MHz=28.000MHz

Please feel free to add some ideas as a comment!

Saturday, January 22, 2011

The JUMA-RX1 a DDS Controlled Grabber Receiver

Yep, this time it's Finnish, guys. JUMA, I guess that is short for JUha (OH2NLT) and MAtti (OH7SV), sells some nice DDS kits. I found them when looking for 136kHz and 500kHz transmitters.

JUMA also offers shortwave kits. I figure, the RX1 kit makes a very nice grabber receiver, covering the 2.2km, 600m, 160m, 80m and 40m bands by means of a DDS VFO.
The rest of the receiver is old skool direct conversion, so using there is no side-band rejection. Not a great deal for 3500800Hz or 7000800Hz, since, not much signal is to be expected below our bands.
The QRSS range in the 2.2km, 600m or 160m bands are at frequencies where the other, i.e. lower, side-band can be occupied. Filtering for those bands will be a necessity. For the 160m band one may consider building a crystal front-end filter for the QRSS frequency. For 2.2km and 600m, this would certainly not do. Not all is lost for LF and MF, since preferred aerials (magnetic loops and frames) are ideally very narrow-band and will, if tuned right, help to at least reduce the lower side-band.
Additionally, filters can be build for the 80m color burst frequency, 40m WSPR and for any other frequency for which crystals are available.

The RX1 kit is all SMD, this could be seen as a hinder by some builders. Personally, I slowly get used to the tiny parts. With a proper PCB holder, a special SMT soldering iron and respective 0.5mm solder SMT is not much harder than regular through hole electronics. SMT has even got advantages, e.g. no excess leads need to be trimmed.

The DDS and the housing alone would justify the expenses of the kit, the DC-RX is essentially for free. Moreover, all mechanical bits and pieces are supplied.
With JUMA even offering the source-code of the firmware for download, which is even written in C, I figure one could easily modify the hardware to a superhet (e.g. 455kHz IF) and program an offset into the firmware.
A possible mod, in my view, could be to have the receiver PCB operated at 455kHz, with a decent IF-filter in place of the 40m low-pass. The DDS-VFO will, in such a scenario, serve an additional front-end, whatever it will be...

Monday, January 17, 2011

28322 Beacon Net Receiver

With the prospect of the upcoming activity in the present solar cycle, it is about time to think of a receiver for the (Italian) 28322(kHz) beacon network.
Due to the nature of those transmitters, the frequency range we want to be looking at is something like 3kHz, maybe 4kHz, i.e. 28320 to 28324kHz.

Now that the task is defined, let's move on and look at the obvious design involving inexpensive parts.

The xx322kHz frequency immediately makes me think of 14.318MHz crystals to form a filter for the intermediate frequency.

With an intermediate frequency of 14.318MHz, a local oscillator should create a frequency of 14.00xMHz. A local oscillator that close to the intermediate frequency will however put unnecessary strain on the IF-xtal-filter and even could end up clogging up a/the IF amplifier. I further believe that LO and BFO being so close is not such a good idea.
Solution to said problems: a local oscillator at 7.00xMHz (crystal easily available) hooked up to a subharmonic first mixer (pair of anti-parallel diodes). The intermediate frequency stage would be blind to 7.0MHz LO stray.

With the mixing all sorted, the next thoughts need to be spent on filter design. A bandwidth of 3, maybe 4kHz, makes a ladder filter a hard task, in particular since such a ladder filter would require quite some amount of poles. Even being harder to make, I figure a lattice filter would be the best option here. Lattice filters however require pairs of matched crystals being a some kHz apart. That is where the work sits in. One pair of 14.318MHz xtals can be selected by measuring/matching the series frequency of stock xtals. The other pair will have be to created by penning down two xtals to the exact same frequency.

For the BFO and the product detector the most obvious choice would be the NE612, just the way one would use it anyway.

Bored of QRSS?
There could be another use for the setup: an SSB phone RX, TX or even TRX. The important bit here, the bandwidth of the crystal filter should be around 2.4kHz. Such a bandwidth is easily available with a ladder filter, however, a lattice filter would give a better response.
Very obviously having a single channel SSB radio at a frequency where beacons beep around the clock is not the best of ideas. So, the LO will have to employ a different frequency. Luckily, many crystals are available for frequencies in the 40m band, e.g. 7030kHz, 7040kHz etc., hence, channelized or VXOed rig is no problem at all. Taking things further, a VFO could be on the wish list. And there is just a perfect option. The famous NE612 (SA612,NE602,SA602) can be configured to operate as a frequency doubling ceramic resonator oscillator. With a pulled down 3.58MHz ceramic resonator (avoid 3.58MHz!), a good portion of the 10m SSB range will be available.

At this place, I would like to thank Jan (PA9QV/OZ9QV) for triggering my thoughts about a 10m upper side-band design with the simple question "do you know a combination for 28322?" :-))

Thursday, January 13, 2011

NE612 Transverter

Something I found on the internet and would like to share:
I have seen NE612 transverters before, those were using two NE612s. JA6HIC uses one chip for both RX and TX conversion. The rest of the design involves an external LO.

The circuit is fed by RX and TX control voltages, this may be handy in places, although I believe that this is merely a remainder of JA6HIC's earlier designs involving diode mixers.
However, I believe a running the transverter from the general supply could be advantageous in particular since there could be a delay between powering down the RX and powering up the TX trains, which could cause the circuit not being supplied and therefore shut down. Using an external LO, it would not matter to shut down the transverter for a moment. However, the NE612 has got an internal oscillator, when using this, we certainly would not like to power down the chip just to power it up again... this would result in terrible chirp.

So, this is my plan: make use of this very simple but elegant design for transverters for 136kHz, 501kHz and 70MHz.  I will be using the internal oscillator of the NE612 as a crystal oscillator. The following obvious options will be available cheaply (the mark (-) indicated subtractive mixing which inverts the band, (*) indicates my preference):
  • 136kHz: 2.000MHz - 160m band (-)
  • 136kHz: 2.048MHz - 160m band (-)
  • 136kHz: 3.500MHz - 80m band
  • 136kHz: 3.579MHz - 80m band
  • 136kHz: 3.686MHz - 80m band (-)
  • 136kHz: 7.000MHz - 40m band
  • 136kHz: 7.159MHz - 40m band (-)
  • 136kHz: 10.000MHz - 30m band (*)
  • 136kHz: 14.000MHz - 20m band
  • 136kHz: 14.318MHz - 20m band (-)
  • 136kHz: 27.000MHz - 11m band 
  • 501kHz: 2.458MHz - 160m band (-)
  • 501kHz: 3.000MHz - 80m band (*)
  • 501kHz: 3.072MHz - 80m band
  • 501kHz: 3.276MHz - 80m band
  • 501kHz: 4.096MHz - 80m band (-)
  • 501kHz: 4.194MHz - 80m band (-)
  • 501kHz: 6.5536MHz - 40m band 
  • 501kHz: 13.560MHz - 20m band 
  • 501kHz: 14.745MHz - 20m band (-)
  • 70.0MHz: 20.000MHz - 6m band (*)
All there is to do is to build an RF-vox circuit and an attenuator (for the TX).

Monday, January 10, 2011

Building a PFR-3A - First Impressions

Building a PFR-3A is not difficult, in fact it is quite easy, although the kit takes a lot of patience.
The first bit of patience I needed for the period between ordering and actually receiving the kit. I ordered November 10th, the shipping documents show that the kit was taken to the post-office December 21st.
I ordered paddles to go with the transceiver, however, there were none in the box, which dropped in January 7th. Although Doug refunded immediately, I would have appreciated some communication in an earlier stage.

The build manual reads that "some of the yellow, monolithic caps may be supplied with the leads being formed for 0.2" lead spacing, while the holes on the PCB are designed for 0.1" lead spacing...". WELL, this is where I needed a lot of patience. The manual should better read that most of the capacitors, be it monolithic or disk type capacitors, are supplied with a 0.2" lead spacing... and the builder therefore should be prepared to bending many many leads to fit the 0.1" spacing used on the PCB.
Ceramic disk capacitors with "narrowed" lead spacing will stick out somewhat higher above the PCB.

Speaking of the manual, there are some errata available on Doug's web-page. However, care must be taken if those are still valid.
Some supplied components may have values other than mentioned in the manual. My kit came with "green capacitors" having a 22nF capacitance, contrary to the listed 10nF. The receiver however, and this is where those capacitors are in, is working excellently.
The manual is short, which I like, but in places it is maybe a little too short. With reference to the schematics, everything can be figured out however.

Another thing that I felt was unnecessary, some of the vias were too narrow, namely the ones of the volume pot and the phones and key connectors. I solved the problem by reducing the width of individual leads.
All of that mechanical work is not difficult, however, it is also not something you would expect building an electronics kit.

The PFR3 employs a DDS. Such systems require calibration. In the PFR3 this is provided by zero-beating vs WWV. Neat, when being able to receive WWV. It would have been nice if one could set a frequency to zero beat against, e.g. RWM, which is much more accessible to Europe.

There is another calibration step, specifically calibrating the BFO. This is done in an ingenious way! Works pretty well.

One thing was striking my eye whilst building the transmitter: L7, which feeds the final, is made from 8 turns #28 magnet wire on a FT37-43 core. To my understanding, in a switch mode PA, ohmic losses should be kept minimal. Consequently, I wound the inductor from 1mm diameter magnet wire (corresponding to #18 AWG).

Enough words, here's some imagery:
some ceramic disk capacitors are bent down to fit the space available

note, the two wires from under the fat red toroid are "binding post wires"

Some additional remark to a comment I found on the internet. I do like the bright yellow color. It makes the transceiver visible, just as intended by Doug.

In an interview on youtube, Doug states, the display was chosen to be LED, rather than LCD, for better visibility in bright sunlight. This only can be a misunderstanding. Clearly LCD would perform superior to LED in bright sunlight. However, I do prefer LED over LCD. In particular red LED is perfect during night-time. Reason: rods do not see red! Therefore, night-vision, which is performed by the rods in our retina, will not be affected by red light, cf. scotopic vision and rhodopsin.

The kit contained magnet wire of several colors, nice touch, I did not need those, since no complicated multi-wire transformers are part of the design. Further I had some electronics elements left overs, namely, 1 transistor, 13 capacitors and 4 resistors, even though the PCB is fully populated. I am not sure what this means, at least I was not missing any parts ;-)

As seen from the photographs, I was ignoring the hook up wire provided in the kit and replaced it by heavier gauge speaker wire.
I also intend to act against the teachings of the build manual by using actual coax cable (RG58 or RG174) to connect the BNC connector to the PCB.

Prospect: This radio will serve me in three functions: it will be a grabber-receiver, it will accompany me on trips and travels and it will be a companion on board of my boat.
And... if time allows (I kinda doubt that), I may write my own firmware for the rig, allowing to receive maritime TTY.

Friday, January 7, 2011

4m & 6m Trapped Dipole

The VRC8000 covers both, the 6m and 4m bands. It would therefore be desirable to use one aerial only for the rig. Quick and dirty idea, a trapped dipole.

Assuming a trap frequency of 70.2MHz, the calculated values would be L=0.5µH and C=10.3pF.
Playing with MMANA, I found a span for the 4m dipole of 205cm. The additional radiator wires for 6m would amount to 26.8cm each. In the 6m band, 51.0MHz was taken as design frequency, due to the FM-nature of rig mentioned above.

The design has not been put to reality yet. However, if one wants to play with a simulation, here is the mmana-file:

4m / 6m trapped dipole
1.041e-17,    -1.025,    1.041e-17,    1.360e-16,    1.025,    1.360e-16,    8.000e-04,    -1
0.0,    -1.025,    0.0,    1.642e-17,    -1.293,    1.642e-17,    8.000e-04,    -1
0.0,    1.025,    0.0,    1.642e-17,    1.293,    1.642e-17,    8.000e-04,    -1
1,    1
w1c,    0.0,    1.0
2,    1
w1b,    0,    0.5,    10.280069,    0.0
w1e,    0,    0.5,    10.280069,    0.0
800,    80,    2.0,    1
2,    7.0,    1,    50.0,    120,    60,    0.0
Mod by Joachim, PA1GSJ 07/01/2011 20:33:45
Created by Joachim, PA1GSJ 07/01/2011 20:21:12

Tuesday, January 4, 2011

30m Dipole Coupling Test

Put up a new (novel?) aerial. It is hooked up to the grabber as of 1920z today. So let's see about the results.

First, what was I doing and why?
A regular dipole requires a balun when used with coax-cable. There are a couple of options for a 1:1 balun. I stumble across one that was using a 1:1 isolation transformer. Clever in a way. Another aerial that makes use of a isolation transformer is the Rock-loop, which proved to be a great helper in my travel setups.
In my Rock-loop, I was running the radiator through a toroid to form the transformer's secondary coil.
The question is, would this work for a dipole too?

Let me show you how the attempt looks like...

What you are seeing here is a T80-2 toroid, a dipole made from twin lead speaker cable (both leads in parallel) and some 75Ohms TV-coax.

I have to add that up to now, I just cut 14.5m of cable for the dipole. With 25cm used for the transformer, this corresponds to a 14.25m stretch. Here a velocity factor of 0.95 was taken into account. This still would be too long for several reasons, most importantly, a frequency of 10MHz, not 10.125MHz, is assumed.

In the Rock-loop, the transformer contributes to the loops inductance. In the example of the dipole, this will be the same. Such an inductance will further shorten a resonant dipole, this has not yet been taken into account yet. I guess, I will wait for warmer days and then use an antenna analyser and a pair of scissors.

All in all such an aerial should be relatively low noise, since it is isolated through the transformer.
The first observations over a span of about an hour are encouraging. I wonder if and how the aerial would, once resonated, perform in transmit.