NE612 Transverter

Something I found on the internet and would like to share:
http://www.geocities.jp/ja6hic/rig/6/trans.gif
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).

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.

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
*
50.5
***Wires***
3
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
***Source***
1,    1
w1c,    0.0,    1.0
***Load***
2,    1
w1b,    0,    0.5,    10.280069,    0.0
w1e,    0,    0.5,    10.280069,    0.0
***Segmentation***
800,    80,    2.0,    1
***G/H/M/R/AzEl/X***
2,    7.0,    1,    50.0,    120,    60,    0.0
###Comment###
Mod by Joachim, PA1GSJ 07/01/2011 20:33:45
Created by Joachim, PA1GSJ 07/01/2011 20:21:12 

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.

Getting ready for the 4m band

If all goes according to plans/wishes, Dutch radio amateur will soon be allowed to use the 4m band between 70.0Mhz and 70.5Mhz. Trying to avoid the mistake of being surprised and hence not properly prepared for 600m, I started considering options for 4m.

First thing was looking for available surplus/commercial equipment. Unfortunately, in this range, all available surplus rigs are providing FM only. Best candidate so far, the VRC8000; actually, I plan to pick up one, before they are all gone. Advantage of this rig, it will also cover 6m.

I guess, a lot of operation will make use of CW and USB. Since no commercial rig seems available, a transverter could be the best shot here.
There are two CMOS oscillators available which would be suitable for the job converting/transverting to the 30m band: 60MHz (regular mixing) and 30MHz (subharmonic mixing).
Another two CMOS oscillators would enable us to convert the 4m band to the 6m band: 20MHz (regular mixing) and 10MHz (subharmonic mixing).

For being prepared, I will to pick a VRC8000 asap, and also consider to build a subharmonic transverter for the 6m band.

AKAI APW20 World Receiver

A new member to the receiver collection, the AKAI APW20. The device grinned at me in my local entertainment shop and for just 75 Euros... too seductive.

I will spare you most of details that can be found on AKAI's website. Here are just some interesting bits and pieces.

On LW, MW and SW, small tuning steps are 1kHz. For SSB a fine tuning pot is present. When rolling over frequencies, no (stupid) mute function interrupts audio.

LW goes up to 519kHz, covering NAVTEX, which I could directly hear from my living room.

Although the receiver has got a connector for an external SW and/or VHF antenna, the unmodified receiver does not switch to an external aerial for neither LW nor MW.

The rotary encoder not only changes frequency, is also can be used for adjusting volume. There is a line-out jack (grabber) and also a line-in (?). The rig is provided with a mute button, which will mute the loudspeaker and phones but not line-out.

Added bonus: built-in thermometer.

The APW20 may not be the best world receiver in terms of ham-radio, I believe however the APW20, in its intended function, is the best world receiver in my collection. I may even reach out and get a second one tomorrow, one for the boat, one for the suitcase.

600m QRP TX at the Plumbtenna - VFO Range

Did some additional soldering on the 600m QRP TX, which is now foreseen with a BNC antenna socket. Hooked up the Plumbtenna (matching&coupling details) and just went for it.

The first tests, once again, were done indoors, from the ground floor.

Lots of plasma TV lines. It seems clear that the Plumbtenna actually radiates, at least a little bit. The HF3's AGC is clearly pulled (ant: Octoplumb, 2 stories higher). I did a little keying, nothing of significance though.

The spectrum indicate a VFO range from just below 501kHz to 503.2kHz. Fingers crossed that this will fall into the range (hopefully) to be assigned to radio amateur at the WRC12.

600m QRP TX update

It is about time to hurry up. Just a few more days and my 600m permit will have expired. As my energy slowly seems to be returning (don't ask what drained it - the regular reader may have a clue though), my soldering iron heats up more regularly. Today, the last drips of solder are dropped and the 600m exciter (see earlier post) has been given a "power stage", namely a 74HC240 operated at 8V.

Just applied some power, no keying yet... neither an aerial, just a few centimeters of wire. Still my grabber's AGC was pulled (tx-ing from ground floor through two reinforced concrete ceilings).

The spectrum shows DI2AM at 505180Hz. The signal at 503200Hz (1955z) would be me testing.
The HC240 developed slightly elevated temperature. I guess this is normal when running it at 8V. I said, the signal was not keyed, and it wasn't, however, I was handling the PCB, feeling temperature etc, hence the variation in signal strength.
I hope that, later 2nite, I will have hooked up a QRSS keyer to the transmitter and have it wired up to an aerial (I figure that will be the original Plumbtenna).

I/Q-SDR Local Oscillator

Just an idea, have not tried it yet... Inspired by YU1LM, I thought of a frequency independent method for creating the I/Q phase shift of 90 degrees.
You may remember my sub-harmonic approach at half the operating frequency. Here a RC network took care about the 45 degrees phase shift. An RC network is ideal for a 45 degrees shift, since R=XC; this was the trick in the sub-harmonic case. However, such an RC network is only accurate in a narrow stretch of frequency.
In YU1LM's designs, a similar RC network is used for oscillators on the operating frequency and on twice the operating frequency.

Twice the operating frequency is a very appealing thing actually. Frequencies are not so terribly high in comparison to the traditional four times the operating frequency method. However, said last mentioned method creates exactly the shift required, due to the purely digital character of the design.

So, why are twice the operating frequency local oscillator so interesting? Very simple, we have QRP crystals for every band. The QRP frequencies are traditionally on the higher end of the CW portion of a band. Divide that such a frequency by 2 will get us about in the middle of the "regular" CW range of the band one octave lower. Examples:

1. 28.060 / 2 = 14.030
2. 14.060 / 2 = 7.030 (here we actually hit the QRP frequency)
3. 7.030 / 2 = 3.515
4. 7.040 / 2 = 3.520
5. 3.686 / 2 = 1.432 (3.686MHz is a cheap standard crystal)

With a sampling rate of 48kbps, this will cover approximately +/- 24kHz about the center operating frequency, and thereby a substantial portion of the CW ranges.

I hope, that I could come up with a pure digital design that will function independently of the frequency it is used at, i.e. no analogue frequency shifting.
Have a look at the concept (there may be details missing in the schematics!):

How is it supposed to work?
U1A (XOR) forms the typical Pierce type crystal oscillator.
U1B is wired as "driver" and is supposed to provide some pulse shaping. Could be that U1B better should be an inverter, meaning, the input which is grounded here, could be wired to 5V.
U1C is an inverter, thereby creating a phase shift of 180 degrees.
U1D is a driver, keeping the original phase. It seems not necessary on the first glance to have this driver, however, it is important to compensate for the delay created in U1C.
U2A (D-type flip flop) and U2B are configured to divide the incoming frequency by 2. Dividing the signal frequencies by 2 means that the 180 degrees phase shift created by U1C and U1D will be just 90 degrees at the frequency divided signals.

Added bonus: I/Q reversal could easily be realized by swapping the roles of U1C and U1D by means of a simple dual toggle switch.

I figure, this design could actually be relatively universal, since Pierce type oscillators are rather forgiving what required passive components is concerned. All the rest is just digital ups and downs, ergh, highs and lows, I wanted to write.

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 ;-)