Construction 2
Following some 18 months of operating my Phoenix valve TX with good results I wanted to build a second unit with some additions. The Phoenix has 2 drawbacks. Firstly the power output is restricted to 3 watts as higher power pulls the VFO causing chirp, and secondly the VFO is prone to drift as the valves warm up. It is also sensitive to mechanical vibration. The simple solution was to use crystal control for the oscillator. Although the Phoenix covered the entire 80 metre band I found that during operation I only tended to use the QRP end of the band. I spent quite a few hours searching the internet for a suitable design. The design I chose was from an American amateur AA7JC. The circuit came from a 1965 ARRL publication and was single crystal control for 40 metre operation. The circuit was simple, employing a single 6DQ6 valve for the oscillator and PA. I constructed the circuit on an experimental chassis with an external power supply. The unit functioned very well, I used a few crystals, principally the G QRP frequency 7.030 and the Fists frequency 7.028. It soon became apparent that changing crystals was inconvenient, plus I wanted to incorporate 80 metres. When I built the final chassis I mounted 12 crystal holders on a PCB, and selected 9 of my favourite frequencies from both 40 & 80 metre bands. Changing crystal was achieved by using a 12 pole switch mounted on the front panel.. I left 3 of the crystal holders free for future use. To change from 80 to 40 I wound an 80 metre tank coil with a centre tap for 40 metres, switchable by a single switch. I used a similar steel enclosure for the chassis as used on the Phoenix. Under chassis construction was simple with minimum of wiring. On power up the unit did not function correctly, high anode current on key down with only about 1 watt rf output. I damaged 2 6X5GT rectifier valves (thank goodness for buying 15 in a job lot on Ebay) before realising the torroid chokes used were unsuitable. I replaced the torroid chokes with 2.2mH RF chokes and this solved the problem. Two 55 ohm resistors were fitted in the output of the transformer to help protect the rectifier valve from any future excess current. The original circuit claimed an output of 15- 17 watts using an HT of 380V, I used an HT of 350V giving a power output of 10 watts on 40 metres and 8 watts on 80 metres. In order to comply with G QRP I fitted a 330watt resistor (switchable) in the anode circuit to restrict the power to 5 watts. The unit incorporates a mixture of old type octal valves and an aluminium electrolytic capacitor with modern contemporary switches, but the overall effect looks pleasing to the eye. On air results have proved successful, some offset from each crystal spot frequency was evident due to the capacitance effect of the wiring running through the 12 pole switch, although there was not any drift apparent.
Valve Transmitter for 40/80 Metres - by Stephen Cruise M0CUT
My SW40+ - Tony GØPEH After seeing the article in the Fists club web site about the Small Wonder Labs qrp transceiver kit I decided to send for one and have a go. The kit can be ordered to cover a single band in one of 80m 40m 30m or 20m.I opted to build the 40m kit. The supplied kit is excellent and complete but if needed one can now buy an enclosure kit as well. As is my usual way I made an enclosure from 1.6mm sheet aluminium to suit this little rig, see photo for more detail.Building is fairly simple as the supplied pcb is screen printed with location and each item to be fitted is notated making it difficult to make a mistake. The build instructions come on a disc and are fine.
For members of the Fist cw Club there is a very good set of instructions by Paul MØBMN including colour photos of each section of the suggested build. One cautionary note here, the parts listed are for the 80mtr kit and some parts vary for other bands so if using these instructions one must make a note of the differences.Once I started the build all went ok and the set up tests went ok. I did have a slight problem with the output but some help with this cleared the prob. It appeared the PA transistor was not working very well but once replaced the rig gave a creditable 4 watts out so was well pleased at this.A quick try out on the band found a DL1 and an SP7 using my G5RV as the antenna so all is fine business. Note also that the kit includes a side tone so you can hear what your sending, a must in my opinion. Also in the photo of my completed rig there is an extra button and a 3.5mm socket on the left of the controls. These are for a mod I hope to fit, that is a K1EL single chip keyer.
Some time in the future and with my love of building qrp gear I hope to make a small (very small) ATU to cover just this band using my long wire and counterpoise which is a favourite of mine when working /portable.As I write this I see from Dave Benson?s web site that orders for this little kit are running a bit behind so you may need a little patience if your thinking of having a go.
QSZ - This meaning is given in the list but in fact many operators send their name and location, i.e. their home town, twice in any case. Sometimes more than twice if they think the other operator will not be familiar with the towns strange spelling. (for example, Strzyzowski)
I wanted to construct a receiver to work in conjunction with a CW valve transmitter that I had built. I tried first a regenerative, then a DC conversion receiver, but quite honestly I found their performance disappointing. There were the usual pitfalls like poor selectivity and AM broadcast break through. After searching the internet I found a suitable circuit on the website of Harry Lythall SM0VPO. I found his site very informative and within the receiver section he showed a circuit diagram with comprehensive details regarding coil winding, set up and alignment procedures.The receiver in question was a general coverage receiver for the ranges 550Khz- 32Mhz with an IF of 455 Khz. This seemed to encompass most of my requirements. The original circuit used 2 pole 6 way switches to cover 5 wavebands. As I only required 3.5- 4 Mhz and & 7- 7.2 Mhz this simplified the switching arrangement. There was not any detail for the chassis layout so I decided to make a prototype first to iron out any problems before building the complete radio on a decent chassis. In addition to the standard circuit I added the following features, RF Amp, product detector, AGC, CW filter and signal strength meter. I used a twin 75pf variable capacitor for the main tuning and local oscillator, but I found that this covered too much of the broadcast band and gave me only a narrow portion of the tuning dial for the ham bands. I was lucky enough to find on ebay a dual gang 11pf variable capacitor with a built in reduction drive and this in conjunction with the 6:1 reduction gear in the main tuning dial gave adequate tuning control. The circuit for the product detector came from an old 1964 RSGB publication. I could not see any performance advantage over the original diode detector, plus audio microphonics proved too difficult to cure, so I reverted back to the diode detector.I am pleased with the overall performance of the radio. CW and SSB can be received under busy band conditions. I found that low powered QRP type signals lacked enough strength to deliver the sort of audio that made for comfortable listening through the loudspeaker, but by using an external audio amplifier the audio level could be amplified without problems of excessive background noise. This was not really an issue as I use mainly headphones for copying CW The circuit ended up incorporating some solid state components. After trying 3 different signal meter circuits using valves, none of which were sensitive enough to display a reasonable comparator for the strength of signal being received, I decided to build a small amplifier using the LM386 IC.I have made a number of QSO?s using the receiver and overall I am pleased with its? performance.
Valve Superhet Receiver for 40 & 80 Metres Bands ? Steve MØCUT
Items on Page * Valve Transmitter for 40/80 Metres * SW40 * Valve Superhet Receiver for 40/80 Metres * Answer QSZ
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