After thinking about my next construction project, I decided to have a go at building from scratch the old P.W. Dart Double Sideband Topband Transmitter, which came from Practical Wireless in Nov / Dec 1983. The components were all easy to find and I already had most of the small components. This will make a nice complement to the RAT5 Receiver and Multi-Rock II VFO.
I used the PCB designs in the magazine and set about making my own boards. There would be three boards…audio board, mixer board and PA board. Later I decided to build an extra board with an ‘RF sniffer’ connected to an LED so that I could monitor the output. The circuit uses a diode mixer SBL-1x which is similar to the MD108 that I used when I built a transceiver using SL600 chips many years ago.
With the boards now completed, I bought a matching case to the RAT5 and Multi-Rock VFO II to mount the boards and build up the wiring and controls. I took the PA tuning capacitor from an old ATU that was given to me. I bought a CB microphone from Maplin to use with the transmitter.
The completed P.W. Dart
When I tested the transmitter I had some RF feedback, but managed to cure this by adding more decoupling capacitors on the audio and mixer boards as well as making sure that everything was properly earthed including the screened cables. I have been getting good reports locally even though the output of the transmitter is just 2w. I can also see my transmissions on G4HYG’s on-line SDR Receiver. I have found this very useful to monitor my transmissions and set up the audio and PA output.
This is the first project for many years that I have built from scratch, which included making the printed circuit boards.
Although I have used FT8 a lot on HF, I would like to try it on 2m and 70cms. Trouble is that there has been some confusion about what frequency to use. In this month’s Practical Wireless there is a short article about FT8 on 144Mhz and shows the actual frequency used (144.174Mhz) I have given it a try, at first I heard nothing, then after an hour or so a couple of stations appeared and I worked them. Later it became even more active and I managed to work 15 stations, one in Scotland, a couple on the South coast and two French stations. This is a wonderful mode for working DX on VHF when the rest of the band is dead. In the olden days predicting openings and lifts became an art. Nowadays high pressure over Europe and all the tell tale signs of a lift leaves me dissapointed because there is not the activity that we had in the past. I think FT8 gives a bit of a boost towards working more distant stations.
Another thing that I have noticed over the last couple of days is the occasional ‘ping’ of Meteor Scatter reflecting FT8 signals from distant stations.
PSK Reporter showing the many spots picked up over the last 24 hours.
The Multi-Rock II is an addition to the RAT5 receiver. It is a programmable DDS frequency generator designed to use as a VFO with the RAT5 receiver and FAT5 transmitter. It can also be used as a signal generator to test equipment. It used PIC processsor chip and already assembled DDS generator. With the success of my RAT5 receiver, I decided to have a go at building this kit and build it so that it matches the RAT5. The kit is fairly straightforward to build, if you follow the instructions, but you have to be careful with the soldering as the tracks are very small. There are two separate boards to build and they are fixed together using solder-in pins.
This is a nice project to build, I have not built anything like this before. When I first switched on to try the MR2 I followed the set up instructions, these are a little complicated as it means pressing the control buttons in sequence. I had a bit of a hicup at first as the frequency control didn’t change frequency! After spending a while checking and measuring I discovered a microscopic short between two tracks. I managed to clear the short with a craft knife. Once cleared, I realised that there was a fault in the PIC chip, it was stuck on channel 2. With some help from Eric GW8LJJ he kindly sent me another PIC chip. This solved the problem!
Now all I need is a case. I looked at the supplier that I used for the RAT5 receiver and they make one which is a perfect fit for the MR2. It needs modifying slightly to ensure that nothing touches the case.
The RAT5 receiver needed modifying to accept the input from the MR2, which was easy enough to do. I also added a switch so that I could change from the external MR2 VFO to the internal VFO.
The MR2 works great with the RAT5 receiver, I have programmed a few channels so that I can just switch to a fixed frequency on Topband or use the VFO to tune the whole band.
Latest addition to my ‘Codar Project’ is to try to get hold of an old Codar PR30 preselector to use with the RAT5 receiver. These are not easy to find, so I put an appeal on the Facebook page to see if anyone had one lying about. A big thanks to Evan who responded, he had an old rusty one in the shed with a load of other junk and kindly sent it to me.
When it arrived I had a look inside, it was like new! The case was badly rusted, but that just needed cleaning up and a fresh coat of paint.
Originally, the PR30 used an EF183 valve, but of course, this means building a PSU to power it or somehow connecting it to the Codar AT5 PSU. Instead,I decided to change it by building the later PR40 circuit, which used a FET instead of the valve and runs on 12v. I built a printed circuit board for the first time in many years and mounted it using the same holes as the transformer would be. There were several versions of the PR30, some with PSU and some without, mine was originally powered by a Codar Valve Receiver.
I had to remove the anode choke and use it in the collector of the output circuit. The new circuit works fine! The front end stayed exactly the same and testing it through all the bands gave a very sharp peak in selectivity. The gain control gave ample (if not too much) gain throughout. I changed the old coax socket to a phono socket and replaced the screw on antenna terminals with another phono socket. These will work fine on Topband! I also replaced the switch on the rear panel, this originally shorted one of the aerial connections to earth so that you can use a dipole or wire aerial. Now it is used to switch through the aerial with or without the preselector, which is very useful.
To finish off,I added an LED indicator, new knobs, good clean and a coat of paint!
Now it matches perfectly with the AT5 and RAT5…
After completing rebuilding the Codar AT5, I decided that I would like to have a matching Topband AM Receiver to go alongside. After doing some searching on the internet, I found a nice circuit which used a single TDA1072A chip. This chip was used a lot back in the 80’s and 90’s for AM car radios. Building the circuit would mean starting from scratch and that would involve making a printed circuit board and finding all the components. As I soon found, some of the components needed were now obsolete, especially the TOKO coils which are like hen’s teeth nowadays!
After hours of searching I came across a kit which was made years ago called the RAT5. This used the almost identical circuit of the TDA1072A, but with additional features including a squelch circuit. The RAT5 was initially designed to compliment the FAT5 A 50W+ Class E solid-state AM transmitter, which I also sold as a kit. Mine will of course compliment my trusty valve Codar AT5.
The kit was supplied by Eric GW4GTE http://www.shortwaveradio.co.uk/rat5.htm
I sent an e-mail to Eric to ask if he still had one of the kits in stock, he does….so my problem with making a PC Board and sourcing components was solved!
I was really looking forward to starting this project, all the components ready including the TOKO coils.
The completed board ready for testing. The kit comes with a very detailed set of building instructions along with testing and alignment. The receiver worked first time when I switched it on (after doing some initial measurements to ensure that I had not made any big mistakes) My next step is to find a suitable case for the receiver, I wanted one that will match the Codar AT5. This was not easy because at one time U Shaped boxes and chassis were 10 a penny, but now nobody makes them. I eventually found a UK source of nice aluminium cases, but the one I wanted was out of stock, so I had to settle for one smaller.
This is a neat little case, very well built. Once I had tested the circuit board I removed the potentiometers from the board and extended them to fit into the case. I also wanted a slow-motion drive for the VFO. My first topband transmitter had an Eagle Vernier Dial, I was going to try to find one for my receiver, but I realised that it would be too large, instead I found a smaller, but similar drive on eBay.
Now I know that this is Topband AM Receiver, but it would be nice to be able to listen to SSB and CW stations as well. To do this I made a simple BFO using a 455khz IF coil (left) It took a bit of fiddling about, but I got it working fine. The BFO just couples loosely to the board to insert the 455khz signal.
Looking good! Just the final alignment now, although the Vernier Drive was a bit troublesome, it kept sticking and needed to make sure that everything was mounted in line.
For the lettering, I sent for a sheet of white decal paper and experimented with letter size on my computer.
This has been a very satisfying project, the RAT5 is very stable and sensitive receiver, the S Meter and Squelch work well! I now use the receiver along with the Codar AT5 transmitter for the Sunday morning 1963khz AM net.
My thanks to Eric GW4GTE for his advice and additional material. A nice project!
A new addition to my shack…
I have used my Yaesu FT857D and FT450D for years now, but have found that working stations in pile ups and noise is frustrating. My voice is fairly quiet and I have to ‘talk-up’ the microphone in order to work stations in contests. The modern Yaesu transceivers seem to lack a good speech processor. When I saw the SOTABEAMS Speech Compressor Kit advertised I realised that this is what I need. I ordered one and built the kit, which is very easy to build and set up. Now I have the ‘talk power’ to get through the noise, reports from stations are excellent and it really makes a difference!
Although the Speech Compressor is really meant for the FT817, it works really well with both the FT857D and FT450D.
After the storm…
After one failed attempt to get the aerials down, I got in touch with my friendly aerial rigger to come and have a look. Even though the weather was still atrocious, they went up their ladders and brought my aerials down safely. They will come back later to put the aerials back up again. When the weather eased and became sunny again I spent some time cleaning up the aerials and greasing all the fittings with Vaseline. I decided to fit my new (very expensive) Yaesu G-450c rotator to the stack of aerials. When I had everything ready I sent a text message to my riggers and they came an hour later to erect the new set up. New heavy duty K and T brackets along with scaffold quality pole fitted and now I have a nice new rotator and aerials that are much higher than before.