That sound is incredible. And such a simple block diagram... I think I need to experiment with a single conversion like that. Thanks for posting, and for the extra sample audio at the end!
Cheers. I suspect I will make this a transceiver. I fond power amplifiers bit of a black art sometimes. For this 'simple' rig it will also be something simple. I'll have to put some thought into it.
Charlie, thank you for the project which has helped me enormously. I have made a valve transceiver using very similar scheme and have used your design of mixers with great success. However I use a bi-directional amplifiers for RF and IF (two valves). I am still a bit short of AF gain however for speaker operation because there are limitations with the valve amplifier with noise and stability. I have a really good AF CW filter using toroids in a third order Butterworth filter, which is excellent. Receiver is just so quiet and sensitive. TX is giving 20W PEP so far as I cannot get enough voltage for the PA just yet. Mixing freqs the same as you but I have a pre-mixer for 7 MHz.
The idea of amplification before the crystal filter seems wrong, you don't want to amplify the signals that are outside the passband of the filter. Perhaps the pre-filter amp should have a gain no more than the insertion loss of the filter, and the post-filter amp should have enough gain to bring the signal up to the required level for detection. On transmit, the total amount of amplification required is less as the balanced modulator can provide a good level of signal.
@@CharlieMorrisZL2CTM Generally you don't want to amplify unnecessary signals because it will cause additional harmonic distortions and IMD. There is a great paragraph (in the second chapter, if memory serves) on measuring amplifiers in EMRFD. The experience of measuring an amplifier according to this paragraph was most enlightening. However! In this circuit you are placing an amplifier on the IF output of DRM. This is something worth doing, but you also have to use a 6 dB attenuator on the input of the amplifier. This will create a vision of ~50 Ohm load to the mixer and prevent any reflections of the signal back to the mixer (which will pass through since DRM is a symmetric circuit, then reflect from RF if it's mismatched on resulting frequency, and mix again with LO, producing unwanted signals). This topic is very well covered in EMRFD as well. An attenuator may be not needed depending on the input impedance of the amplifier, which may also depend on it's load.
Very nice. Hopefully I will have a receiver step up soon with my weird configuration of using 10.7Mhz filters. Still goo to build my IF amps but they should be simple enough.
Work of art and science! Wonderfully laid out and explained. I really wish i could've seem you working on this part via a live steam! I am being greedy in asking you to show us how you actually solder and build things - even a small portion would be great. Also, may I request you to tell us how you wired up the antenna coax to the first switch. A cct diagram would help for beginners like me fir your entire layout so that we can replicate and learn. Which coax cable do you use for inter module connections? IS it RG174?
Thanks Rajaram. I do have a video on how I make the circuit builds. Unconventional, but it works for me with the freqs I am interested in. The coax is RJ174. I often just use hook-up wire if the modules are close enough.
@@CharlieMorrisZL2CTM Thanks a ton for your reply Charlie! Do send a link to the build video you've mentioned above in your reply. I'm really grateful to you for your sharing your precious work with all of us.
Is this crystal filter a regular 8 pole filter or a 6 pole QER-filter (with parallel crystals on input and output)? What's its input/output impedance? Could you please show its frequency response?
