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.

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.

High IF

The high shortwave bands 24 and 28 MHz are difficult when using 27 MHz as IF.
I am considering to build a simple transverter to a high frequency. I can be made similar to the one described in this blog.

The 27 MHz trx transverter combo can be used as IF for the shortwave transverters.

50 MHz could be used as IF. All I need is a 23 MHz xtal, a mixer and some filters.
A preamp may be needed as well .This way I have a 50 MHz radio too.

A better option is to build a transverter to 70 MHz. Currently PA land does not have an 70 MHz Ham allocation. This may change in the future though. 70 MHz Is a better IF than 50 MHz. Besides, SAW filters are available for this frequency. Those could be used as roofing filter.

A lot of conversion is done in this concept. The SSB signal will surely degrade by those conversions. It should be possible though after all some ham radio's use 4 conversion too.

USB synthesizer

At the annual radio market in Rosmalen I bought a USB synthesizer kit.
See SDR-KITS
It uses the si570 to generate signal between 3.5 MHz and 180 MHz.
This unit can provide all frequencies I need for the all-band version.

Power output is a bit low. I will amplify it using a MAR amplifier. That should not be a problem.

The synthesizer is USB controlled. I will use a PC to control it. I might add a micro controller board later.
However, I am considering to make it a PC controllable Transverter.
To do that I need some USB controllable I/O ports. I could even make a PC controllable transceiver.

The power amplifier I will use is 5 Watt amp box73 it is a 5 watt amplifier that works from 1.8 to 144 MHz. So I can even add 50 Mhz an 144 MHz.

More design considerations later.

allband version

I have investigated the possibility to build an allband version.

A device Si570 could be used to generate all signals. The CB set can be set to a fixed frequency. A microcontroller, LCD and rotary encoder can be used to control the Si570.

It should be possible to build one for most HF bands. However 28 MHz will be difficult. The Mixer will leak some 27 MHz. A suppression of 40 db is possible but it is hard to accieve. The 28 MHz bandpass filter won't provide enough attenuation.
I think that 24 MHz will be difficult too.

For 14 MHz and higher a preamp between the mixer and the bandfilter may be needed for reception.

Using a Lo signal that is higher than the reception frequency is needed for bands > 10 MHz. LSB and USB will be switched. I better use it for all bands. it will reduce software complexity. An additional advantage is that the Lowpass filters can be used to reduce mirror image reception.

80 meter version

The design can be adapted to 80 Meter. making a suitable LO signal may be a bit difficult though.

Two 23.5 MHz xtals are required (27-3.5). These are non standard as far as I know. 30.5 (27+3.5) MHz can be used instead. Those are nonstandard frequencies too.
using 30.5 inverts LSB and USB.

23.5 MHz can be generated by dividing 47 MHz by 2. You could try to use a VXO at 20 MHz. Then double this signal and mix it with 7 MHz.

A band 300 KHz wide band filter for 80 meter can be found in the Elecraft K2 design.

Almost ready

The transverter is almost ready. I could add the bias current temperature stabilizer.
I might do that in the future. It may be good enough though. I have reduce the power to 5 Watt so it is not getting that hot anymore. Five watt is enough to drive my lineair amplifier.

I tried to make contacts using it bare bones. So far I have not had any luck. It should be possible though. I have a lineair amplifier that can provide 200 watt PEP using 5-10 watt drive. I will use that amplifier to boost the signal. It should make things easier. In the future I may build a PA for the lower bands using IRF510 fets.

I will try to make a movie clip showing its receive capabilities.

New output transformer

I made a new output transformer for the PA. I used less turns and more ferrite.So I was able to use wire with a larger diameter.It worked out fine. I can get a bit more than 10 Watt output, measured after the low pass filter. Input current was 1,8 Ampere. This result is OK.

The transformer has 2*2 turns primary and 9 turns secondary. SM0VPO uses 3*3 turns primay and 16 secondary.My transformer is made by 3 2 hole ferrite cores. Brand is unknown. This is the third transformer I tried. My maximum power is limited to 12 Watt theoretically. That is OK I will use the PA at 7-8 Watts maximum. The SSB signal sounds good on my receiver. I didn't notice splatter on nearby frequencies.

I really have to implement temperature compensation. Now It suffers from thermal runaway (DC bias current increases when temperatere rises). For SSB speach it is not a problem. It is a problem when a carrier at full power is being transmitted (AM mode). AM is not needed ,I (mis)use it for tuning the antenna though.

Low pass filter and fan regulator

I just built the Lowpass filter using info from the ARRL handbook. I have used the 5 pole Chebychev filter. That sould be enough. It seems to work although I can not measure its characteristics yet. The output signal is not attenuated much. the output looks clean on a 100 MHz scope. I have to wait until my spectrum analyser project has finished. Than I can be sure.

The PA does not have enough cooling, so I added a fan. The fan starts when a transmission starts. After the transmission stops, it stays on for a few secons. I made a circuit to accomplish that.

After pushing the PTT switch I hear a tjoep signal on my SW receiver. I will have to find out why that happens. It is a bit anoying.

I found a similar power amplifier in a previous project. That PA has a better output transformer. It puts out 5 watts too but the efficiency is much better. I 'll rebuild the transformer using the same ferrite core type.Then I may get out a bit more power. That would be nice.

amplifier news

This picture shows the amplifier.

It is not 100% the same as the SM0VPO amplifier.
I did not use a thermistor in the the bias current regulator. When I find a 1K thermistor I will add it. Now I just use a 1 K resistor. The bias circuit for the driver is different too. I don't remember why I changed that.

The amplifier works but I can only get 5 watt output. I add a few capacitor to smoothen the base and the collector voltages. They are sinus shaped now. Without those capacitors the signals cointains spikes.
A problem is that collector voltages reach their maximum at 7 Watt. That should not happen. I tried different ouput transformers but the results are the same. The output voltages divided by the input volatges just doesn't match the turn ratio. Input current of the finals is 1.5 Ampere for 5 watt output, so the efficiency is low too.

I will have to investigate what is wrong meanwhile I keep using amplifier as it is stable. I did not see it oscillate, even when SWR was high. The output looks clean.
Then I checked the audio. It souns good on a shortwave receiver.

Next task is to improve power and efficiency and build a lowpass filter.

Power amplifier.

Some time ago I tried to build a 10 watt amplifier for all HF bands. I found one designed by Harry lythal SMOVPO. See 10 watt hf amplifier It did work but I had problems making it work for all bands between 3 and 30 MHz. If I remember correctly it worked fine up to 10 MHz. It was unusable back then.It should be fine for 40 meter though. I will try to make this amplifier work again. The output transformer and the input transformer are missing so my next task is to build these transformers again.

Meanwhile I found a suitable enclosure for the transverter. On I flea marked I bough a automatic printer switch. It is obsolete but it is build in nice a solid metal box.That box makes an ideal enclosere for the transverter.

scratch schematic diagram

Here is scratch diagram of the transverter. I will make a better drawing later.

The lowpass filter at the output is not ready yet. A PA will be build to boost the signal to 5-10 watts.

Super VXO

I was unable to get 20 KHz tuning range using varicaps. So I tried a variable capacitor instead (not a trimer). The tuning range increased to 14 KHz but that is not enough.Then I added a coil in serie with the varco. No luck, 16 Khz was maximum.

Finally I tried the super VXO configuration (2 xtals parallel and a coil in serie).
That did the trick. The tuning range is 25 KHz.
see http://www.qsl.net/7n3wvm/supervxo.html for information about super VXO's.