Useable state

After some refinements The transvertor is usable.
However I am not satisfied with its performance. So I will need to make more adaptions.

Problems that remain.

• At some bands edges the harmonic suppression is not good enough. Fortunately the ssb part of the bands are usable. The CB radio has no CW anyway.
• 14 MHz band does not work anymore. One of the relays in the band pass filter is not working . This type of relay is very hard to find as it is some unknown Russian or Ukraine brand. I will have to make an adapter for the relays that I have in stock.
• Power output is low. It produces about 3 watts. |This can be improved  by using13,8Volt instead of 12. I would like to have 5 Watts output.

The positives.

• The receiver works quite well, even on the crowded 40 meter.
• SSB TX signal sounds good

 Some improvements:

• Feed the CB radio from the transceiver. The transformer  inside the transverter is big enough to handle this. When this works I can get rid of the extra power supply.
• make a nice front to make it look better.

lowpass filter

The transverter works but the the lowpass filters are a problem.
I will need to make them myself. 

The attenuation on the second harmonic is just about acceptable on most bands (-40db). on  some bands it less (35db).  I think I understand the reason why.
It was intended for a amplifier that uses a push pull configuration. The second harmonic is suppressed much more. in such a amplifier. I am using a class B amplifier that has a strong 2nd harmonic.

Input Impedances don't seem to be 50 Ohm for all bands. Fortunately I was able to tune it a bit by adding capacitors. That even improved the 2nd harmonic suppression.

picked it up again

This project was on the shelf for a long time.
Now I have picked it up again.

the transverter basically work. Reception is Ok. Listening on the 40M band during night condition is a good test. The transverter seems to work well under those conditions.

after smome test I found that a variable attenuator is not really needed. I have used 2 resistors to reduce the gain until I got  4 watts on 80 meter. On other band the output is between 3 and 4.5 watts.
That is Ok for now,

TX caused more trouble. It has some oscillations that were hard to find.
I have improved the wiring and made a separate 12V supply (7812) for the PA.
The amplifier without low pass filter produces harmonics at -15dbc for the second harmonic.
After I got the amplifier working I connected the LPF. Now the second harmonic is at -40dbc.  This is just enough according our regulations. I had expected a bit more from this filter. Another problem is that at some bands the attenuation is a bit high. I loose 2 of the 4 watts. The filter came from a commercial transceiver. It may be tweaked for that transceiver. Input and output impedance may not be 50 Ohm.

The band pass filter causes some problems. After some tests 14 MHz stopped working.
One of the relays is not working well. I tried to resolder it but no luck. Once in a while it works on 14MHz but it stops after changing band and the change back to 14MHz. I need to replace the relay but this is a Russian type that cannot be found easily here. In fact I have never seen anything that looks like it.

The after a while another problem with the bandpass filter popped up. Somehow the center frequency of 40 30 meters has moved up a few 100 KHz. I have no idea why. I did improve soldering of some components that is the only reason I can think off. Strange, I have never seen this happening. The tunable cores are glued in place so I don't see any problem there. I will try to tune it by adding small capacitors.

Pindiode experiments.

I bought a couple of pindiode to make an ALC for the transverter.  It must be a voltage controlled attenuator.

The attenuator worked but I am not happy with the performance. The performance is probably Ok for weak signals but my signal levels are much higher. I see too much distortion of the signals.

Another problem is that the 2 MAR's and the PA sometimes oscillate. I think it can be solved by adding an attenuator between the 2 MAR's. Between the MAR's I will add a fixed attenuator. Before the MAR's I will add some switchable attenuator..

High IF results.

I did some test with a high IF to see if this is a good idea.

I used a 40 MHZ xtal oscillator block, 2 mixers and 3 tuned circuits at 67 MHz.
The idea is to make a transverter from cb to 67 MHz. That transverter/ CB radio combination would be the IF for the HF transverter.

Results were not as good as I had hoped. Id did work but the intermodulation was way too high. Especially at 7 MHz. Beside that The noise was very high even without antenna. That noise was generated by the 40 MHZ xtal oscillator. I replaced it with a signal out of a HP signal generator. That reduced the noise quite a lot. Unfortunately the intermodulation problem could not be solved easily.

I could have exepected this result. After all modern radio's use a roofing filter.
Those filters have bandwidths of 3 to 22 KHz. That solves some of the intermodulation problems.

I could try to get one of those. However it will increase the cost of this project. The filter is not cheap and I also need an xtal oscillator at an non standard frequency.

So I Think I stick to the 27 MHz IF. The transverter will be usable at 21 MHz and below. I already check the 21 MHz signal on the spectrum analyser. The spurious is -50 dbc. It may even be possible to use it at 24 MHz. Some aditional filtering is needed though

Power amplifier

The 5 power amplfier kit form box73.de was build and mounted on top of the enclosure.
It has a big heatsing so it will stay cool during wspr/qrss operation.

I have also mounted a switchable lowpass filter near the PA. I still have to wire it to the bandswitch.

To drive this amplifier I made a two stage amplifier using mar-4 amplifiers.
A single mar-4 did no provide enough power gain to drive the amplifier. Output power was 1 watt on 80 meter and 0.5 on 12 meter. So I have added another one. Now the gain is more than enough. Actually attenuation is needed to prevent overload.
The plan is to make an ALC circuit using a voltage controlled attenuator. Pin diodes will be used in the attenuator. I have just ordered some.

status update

I have just build some of the components in the box.
The transverter/cb radio can now receive 160-10 meter. It can also transmit a tiny signal.