Taurus

20 Meter SSB Transceiver

I can't seem to get one project completed before I'm looking for my next one. I'm still working on the KK7B R2Pro but while searching the Internet I ran across this 20 meter SSB transceiver. There seems to be an unlimited number of CW qrp homebrew rigs, that one can build, but very few designs for single sideband use. You can find information for this rig here. The site is owned by Wim, SP5DDJ from Poland. I visited Wim's site several times looking at the schematics to determine if parts would be available in the US. I thought the transceiver might be a good candidate for Manhattan style construction. During one such visit I noticed that Wim was offering a set of printed circuit boards for both the 80 and 20 meter versions of the transceiver. I fired off an email, asking about the cost of the boards and Wim responded within a couple of hours with a price of $20 US. For $20 I received two receiver, two transmitter boards and two very nice ceramic trimmer capacitors for the VFO. It took about 12 days for my letter to reach Poland but the circuit boards arrived here in California in about 5 days. The boards are of nice quality, although they are single sided and do not have plated through holes. The same board is used for 80 and 20 meters, with just a change in component values. Wim has translated, into English, information on the 20 meter transceiver and plans to do the same for the 80 meter version.

My parts are just starting to arrive so I'll have more on my build soon. Below you will find the bare receiver board on the left and on the right the board with all of the resistors in place.

Well, things are going fairly well with my build. I was ready to start checking out the receiver board when I discovered that the 50K ten turn pot I was going to use had a bad spot right in the middle of its range. I'm waiting for a new replacement from Mouser, which should arrive in the next few days.

Below you see the mostly completed receiver and transmitter board. I still need a few inductors to get here but other than that it is complete.

                                                                           Click image for larger view

I finally finished up the receiver board. I had a couple of false starts but after emailing Wim I was able to sort everything out. If you decide to build this transceiver, there are a couple of things to watch out for. A few of the components holes on the circuit board are too small for the parts. I had to re-drill the trim caps holes but there was plenty of solder pad so that worked out well. There are a couple of pads marked "24" and I thought they were straps that needed to be put on the board. It turns out those pads are on the board for use as a way to add an external filter. You will need to run a wire from the "24" pad near the lower J310 over to the "24" pad at pin 24 of the MC3369P. The picture above shows the wiring error, so don't put those straps across the "24" pads. There are four places on the circuit board that do need a wire strap, they are labeled Z1 through Z4.  I was lucky that the MC3369P was not damaged by my mistake. Getting the VFO aligned is a little tricky but once aligned it is very stable with very little drift, if any.  Because there isn't documentation in English, I have included the information, sent to me by Wim, for aligning the VFO. I have quoted the email I received from him.

"Hi Bob,

You are doing good progress !

Assuming that you started with 20m band...

You may use frequency counter connected to pins READOUT on RX board or use
your RX you have set around 4100kHz and 4350kHz. In this case use short whip
close to VFO coil as an antenna.

Here you have step by step alignment of VFO:

1.    Set both 47k pots in the middle of its range. They will be used for
range setting later
2.    Set the multiturn pot in the left edge and check if you have minimum
voltage on cathodes of varactors. This will result lower VFO  frequency i.e.
4150kHz after alignment. If the left edge doesn't  correspond to,  change
cables soldered to multipot.
3.    Turn the VFO cap trimmer and find  signal in RX or measure around
4150kHz.
4.    Turning multipot to the right you should increase the frequency. Make
a note what was the highest frequency in right edge of multipot.
5.    Now is the time to set the span and both edges of VFO range. Use pots
47k and find out which is increasing or decreasing span and edge
frequencies.

This is a very nice job to do and feel free to make some experiments. If the
range is to low unwind one turn from VFO coil.

After alignment check voltages on varactor cathodes. You should have approx.
1V in one edge and 6V on the other side. Remember not to go below 1V in the
left edge of multipot ( this is set by one of the 47k pots) because signal
of VFO will be distorted. Make an exercise with this.

Now BFO:

Find a signal in multiband RX around 10MHz ( set rx for CW) and connect
antenna input of this RX to the case of crystal 10MHz using alligator clip.
There is no way to measure this frequency using freq-meter... By turning
slightly trim cap set BFO precisely at 9,996MHz. The same frequency and the
same method use in TX part ( carrier oscillator)."

Here is my finished, working receiver board. The digital readout is one of Steve Weber's counters. Click on the picture for a larger view.

I am amazed at how well the little receiver performs. The audio seems a little weak, for my liking, so I need to look at the circuit to see if I can boost the level from the LM386 audio amp. I am missing a couple of components for the transmitter board so it will be a few days before I can start checking it out. I didn't know, until very recently, that I'm the first person, outside of Poland, to build this rig.

It has been a month since I've posted anything about my progress. My shop is located in the garage and our weather has been very warm. We have had 15 days, this month, where the temperature has been 100F or over. I've made some progress though, as show below.

Most all of the interconnecting wiring has been completed in the above view. Click the picture for a larger view. This was the first time I've used teflon coated coax and I found it rather hard to work with.

I've alway purchased cases for my projects but decided to try building my own from printed circuit board material this time. It has been fun and for the most part things are working out well. I'm not sure how to finish the case, I would like to design an overlay and glue it to the panels but my first attempts have been less than satisfactory. The boards are not secured in the above picture and were put in the case just for the picture. I still need to drill the hole for the microphone connector and then I'll be ready to put the other controls in their place.

I finally got back to work on the Taurus case and got the boards mounted. I haven't attempted to clean up the wiring yet as I'm just starting to do the transmitter checkout. I know it would have been easier to do the check-out outside the case but I find it's easier in the long run because things can change once the circuit is in a metal cabinet. Click on the pictures below to see a larger view.

Well, I finally started checking out the transmitter side of the transceiver. I'm getting an oscillation that is causing the 2N2219A driver transistor to self destruct. Wim has suggested several solutions but I still can't get the transmitter to settle down. I've been replacing the emitter resistor with a larger value but the instabilty is still there. The driver emitter resistor started out at 3ohms and while trying to reduce the oscillations I went in steps up to 10ohms. This didn't seem to make much difference.

At the suggestion of Wim, I put a 100pf cap from the collector to ground on both the driver and final transistor. This seems to have solved the oscillation but I'm still not getting much power out. Here is a picture of the scope presentation, where I'm speaking the word four. This is showing 1V P-P.

I'm still not getting much in the way of output power so I replaced the 10ohm resistor with the orginal 3ohm one. Still not enough output power so I reduced it again to 2.2ohms but that didn't seem to make any difference either. I'll try a 1ohm resistor next and see if it that changes anything.

 

 

 

 

Last updated August 26, 2005