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.

some progress

Last weekend I did a few things. Not as much as I hoped though.

I modified the CB radio. When it transmits it also outputs a DC voltage on the antenna connector. That DC voltage will be used to switch the TX/RX relais.
The voltage is connected through a 2k2 resistor.So a transistor must be used in the transverter to switch the relais.

In the transverter the TX/RX relais circuit has been made. The TX RX switch works fine.

I made a simple lowpass filter for the audio of the CB set.

I did some experiments with varicaps to control the frequency of the LO. I did use a 35pf trimmer. The 20 MHz xtal could be varied 20 KHz using this trimmer. Unfortunately I was unable to pull the frequency more than 10 KHz using varicaps.

power boosted to 5 mW

I made a small amplifier to boost the signal to 5 mw. The first amplifier is build around a bfy 90 in class a. A 2N2219 is used to boost the signal to 5 mW. This amplifier has a tuned circuit.

Initially the power output was much to high. The 2N2219 worked as class B amplifier. I measured 100 mW. So I added a resistor at the input of the first amplifier. This reduced the power to 5 mw.

Now I will add the RX TX relais.

band pass filter

The bandpass filter works fine. It is 200 KHz wide now.

I measured the filtered output during transmission. The filter is terminated by a 47Ohm resistor. The signal has a value of 150 mV pp.

Today I will build amplifiers too boost this signal.

band filter

I made a bandfilter for 7 MHz. It should filter the input/output to/from the 7 MHz port of the mixer.

It consists of 3 tuned circuits. The coils are made by 18 turns on a T50-2 core. Coupling between then is done by a 1 turn link coupling.

It works but I am not satisfied. It is probably good enough but it can be made sharper. I think the link coupling is too tight. The link coupling is a piece of wire (ring) between two cores. This coupling is good, probably too good.
I will change the coupling by a capacitor coupling.

pictures

some results

Last night I reduced the power of the LO amplifier to 5 mw.
Then I mounted the mixer (HPF-505). Now I have a basic transverter.
No band filters were build yet.

I was curious if stations could be received using this setup.After all 40 meter contains a lot of broadcast stations. So I hooked up the cb set to the IF port of the mixer. My antenna was just 50 cm of wire.

I did receive a lot of broadcast stations. I was even able to hear a lot of ammateur stations. That is a nice result. Connecting the antenna increased the noise to S5 level. So a preamp may not be necessary. I'll check again when the bandfilters are ready.

Then I tried to transmit. Success, the LSB signal sounded good on my FT-950.
Of course the output signal is small, a few 100 mv at the non terminated IF output.

During reception I found out that The CB sets produces too much high tones. I already expected this. So I'll have to add a LC lowpass filter with a cutoff frequency of 2200 Hz. I will put it between the amplifier and the speaker. That is not the best solution. However it requires only a small modification of the CB radio.

I started building the band filter and the attenuators. I hope I can finish it today. Soon I will upload some pictures and a schematic diagram.

Building VXO

Last night I built the VXO I also made an amplifier for this VXO.

The VXO can be pulled 20 KHz up with a single xtal and a 35 pf trimmer. Twenty KHz is enough so I may not need the super VXO configuration at all. However the tuning is not lineair. Maybe the super VXO has better lineairty, I will try it later.

For testing a use a trimmer to set the frequency.It will be replaced by a varicap eventally.

The signal out of the VXO is amplified by a 2N2219 amplifier. I delivers 80 mili watt. That is too much, the mixer needs 5 mw. I will reduce the power to 10 mili watt. The output signal will be fed to the mixer via a 3db attenuator. This attenuator wil improve the termination of the mixer.

diagram universe 5500

I have found the schematic diagram for the universe 5500.

Start blog

I have a few CB ssb sets in my junk box.
It is time to use them for ham operation.
Those CB radios can be converted to 10 meter. However 10 meter propagation is poor.So I will make a transvererter to 40 meters.It should not take too much time to build. I have a few other projects that need to be finished.

Building a transverter from cb to one of the lower ham bands has been done before. I found a few examples on the Internet. I expected to find more though, After all a lot of these sets are available at low prices.maybe the quality of the cb sets is not good enough.

The CB radio that I will use is an Uniden 5500. This is supposed to be one of the better CB sets.A transverter needs just a few milli watts so I have disconnected the final and the driver stage. The radio now produces 1,5 milli watts. This signal sounds good on a hf receiver so the basics are ok. I think I will add 12 volts DC to the output signal while transmitting. That DC signal can be used to switch the transverter between TX and RX. AM transmission does not work anymore. That is fine, I don't need AM. Transmitting in AM mode produces a carrier. That is great for tuning the antenna.

A CB radio has a 10 KHz channel raster. However sometimes the space between two adjacent channels is 20 KHz. This raster is unusable so some kind of finetuning is required. The set has a clarifier we hams call it RIT. Maybe it can be modified to work during transmit. However it won't span 10 KHz let alone 20 KHz. So finetuning will be build in the transverter.

Design ideas:

I will build a (super) VXO at 20 MHz. This signal goes to one of the RF pins of a diode mixer. The transceiver is connected to the other RF port of the mixer.
The IF port of the mixer is connected to a band pass filter for 7 MHz. That is basically It. This transverter is bidirectional, no TX/RX switch is needed.
Of course the output is low, I expect 0.5 milli watts. The received 7 MHz signal will be attenuated as well but I guess that won't be a problem.
During TX the signal is amplified to 5 watts. Relais are used to switch between RX and TX. The 3db attenuators are used provide proper match for the mixer.