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.

Multiband HAM to CB transverter

This is the starting point of the multiband HF to CB transverter.
The shown setup actually receives pretty well. I have tested it on 160,80 and 40. The other bands are closed during the night.

The components are:
-CB transceiver. It is modified it has 0.1 Milli Watt output.
-SDR kits VFO using si570.
-A bandpass filter for 160 to 10. Made in Russia, bought on Ebay.
-A HPF-501 mixer and a amplifier using a bfy 90. Using the same concept as my 40 meter to CB transverter.

That is enough to build a converter to CB. It should be able to transmit as well but I have not tried transmitting yet. It will probably put out 0.05 milli Watt.

I have a 5 Watt amplifier kit for 10 to 160 meter. This PA comes from box73 hamradio. I want to use it to amplify the signal to QRP level. The output of the transverter can not drive this amplifier so I need a small amplifier. I may use a MAR amplifier.

The PA kit does not include a heatsink so I will search the internet to get one.
Maybe the local electronic shops have a suitable one but I doubt it.

Lowpass filters are needed to filter the signal out ofthe PA. I already have one. Just another ebay purchase. It was part of a 100 watt HAM band transceiver so it should be suitable for my project. A picture of it will be posted soon.

One of the other projects I am working on is a QRP HF transceiver. I will combine both projects. After all only the LO and The IF frequency are different in those projects. The CB radio will be used on a fixed channel. The IF strip of the QRP transceiver uses 9 MHz. The SDR kits vfo can be setup for another IF offset by pressing a few buttons. It is a piece of cake.

USB synthesizer 2

Last night I finished building the USB synthesizer. Fortunately it worked the first time I turned it on. It works from 3.5 MHz to 180 MHz so I can generate all frequencies I need.

On ebay I bought a bandpass filter unit that has filters for 10-160 meter. That would be ideal for the CB to all HF band transverter.

I am considering to continue in a different blog. This blog is for the simple CB to 40 meter transverter. The new blog will be dedicated to the all band to CB transverter.