28-09-2017, 01:44 PM
An update of progress on my pantry Tx for those who are interested.
I have constucted further modules, on the style shown in my earlier post, for 1j24b, 1j29b and 1j37b. As mentioned, the heater supply I am using is around 1.24V. I have fitted each module with a resistor to drop the voltage to around the 1.1V as Trevor suggested.
Using an HT voltage of 50V, via a supply I have been developing (to be described), I tested each module using a sinewave signal as input. I used a nominal (82kOhm) anode load. Each worked well, the 1j29b having the most gain, 1j24b next and finally the 1j37b. With the 1j37b I tested with each g1 input seperate rather than together so probably not optimum. My plan is probably to use the 1j29b for audio, 1j24b for oscillator buffer and, as planned, 1j37b for modulator / output.
To test the modulator idea I then fed the 1j37b with oscillator output (no buffer) to g1a and a sinewave (not perfect) input to g1b. I was able to display a modulated output on the oscilloscope and pickup the signal on a transistor radio tuned to MW. A better measurement of frequency was determined from my comms receiver which has frequency readout in kHz. Photos shown are the modulated waveform and the rats nest of connections for testing. The modules are neat, but I suppose the mess had to come somewhere! There was very little instability though. Using the modules does permit very easy exchange of valve types during testing. I did tune across the band, but found very very little pickup on harmonics, but at this stage it is purely pushing the signals in at their set output, rather than amplifying and adjusting drive levels.
One thing I found was that with my 165kHz crystal and woring on the 4th harmonic (660kHz), there was a station around that frequency (sounded like BBC). It may be Radio York, but I didn't listen to check. I will perhaps move to a clearer channel. I have 140kHz crystals, but these don't seem very active. I have a 97kHz one that works well. It was giving good output on 8th harmonic when I tested it so may well go with that as it would give more scope for moving channels. One thing I have noticed is that output seems far more prominent on even harmonics. I have seen 3rd harmonic output but really not noticed any other odd ones. My lack of knowledge probably, and maybe not of great concern, but i'll look into if I get chance. It will likely simplify harmonic supression on the output though. I have 1MHz crystals so could go for fundamental but this is a bit of a learning experience as well. In that - it is working!
I have constucted further modules, on the style shown in my earlier post, for 1j24b, 1j29b and 1j37b. As mentioned, the heater supply I am using is around 1.24V. I have fitted each module with a resistor to drop the voltage to around the 1.1V as Trevor suggested.
Using an HT voltage of 50V, via a supply I have been developing (to be described), I tested each module using a sinewave signal as input. I used a nominal (82kOhm) anode load. Each worked well, the 1j29b having the most gain, 1j24b next and finally the 1j37b. With the 1j37b I tested with each g1 input seperate rather than together so probably not optimum. My plan is probably to use the 1j29b for audio, 1j24b for oscillator buffer and, as planned, 1j37b for modulator / output.
To test the modulator idea I then fed the 1j37b with oscillator output (no buffer) to g1a and a sinewave (not perfect) input to g1b. I was able to display a modulated output on the oscilloscope and pickup the signal on a transistor radio tuned to MW. A better measurement of frequency was determined from my comms receiver which has frequency readout in kHz. Photos shown are the modulated waveform and the rats nest of connections for testing. The modules are neat, but I suppose the mess had to come somewhere! There was very little instability though. Using the modules does permit very easy exchange of valve types during testing. I did tune across the band, but found very very little pickup on harmonics, but at this stage it is purely pushing the signals in at their set output, rather than amplifying and adjusting drive levels.
One thing I found was that with my 165kHz crystal and woring on the 4th harmonic (660kHz), there was a station around that frequency (sounded like BBC). It may be Radio York, but I didn't listen to check. I will perhaps move to a clearer channel. I have 140kHz crystals, but these don't seem very active. I have a 97kHz one that works well. It was giving good output on 8th harmonic when I tested it so may well go with that as it would give more scope for moving channels. One thing I have noticed is that output seems far more prominent on even harmonics. I have seen 3rd harmonic output but really not noticed any other odd ones. My lack of knowledge probably, and maybe not of great concern, but i'll look into if I get chance. It will likely simplify harmonic supression on the output though. I have 1MHz crystals so could go for fundamental but this is a bit of a learning experience as well. In that - it is working!
