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26th September 2010 15:35
Hi Alan (and to the poster named "DX"),
I noticed the comment about using a "Pierce oscillator as a regenerative detector running at the 25MHz IF in a super-het project". I am interested in exactly this kind of regenerative crystal oscillator for exactly the same purpose (simple, sharp, stable, no-LC-required regenerative IF stage for a CW superhet).
From my research on the topic, it seems there aren't so many examples of regenerative crystal oscillators using modern solid-state devices. The Pierce topology is especially tempting because of its simplicity.
Would it be possible, Alan or DX, to provide a schematic or a write-up of how such a regenerative crystal oscillator would be constructed with contemporary solid-state devices?
In the mean time I plan to whip up a Pierce crystal oscillator and try varying its voltage to see if I can control the oscillation for regenerative detection use. I seem to recall reading that this doesn't work as expected however.
23rd March 2010 13:14
DAT-31R5-SP is available at this link http://www.herostechnology.co.uk/pages/pages_comp/minicircuits.html
73's Elia, 2E0ZHN
11th February 2010 09:18
Several years back, I've used a Pierce oscillator as a regenerative detector running at the 25MHz IF in a super-het project. Sensitivity was superb (about -100dBm, if memory serves) and the dynamic range was remarkable. Unlike other regens I've built, this one was mostly immune from overload and could readily copy a weak signal spaced 10KHz away from a very strong local source. A 1K resistor had to be inserted in series with the crystal, otherwise the detector would abruptly jump into oscillation. Selectivity was perhaps too narrow for AM reception but while weakly oscillating, the detector would readily phase lock with a carrier.
I'll be sure to test this super-regenerative configuration soon. Your data suggests that the super-regen is less susceptible to response at the crystal spurious resonance frequencies.
8th February 2010 14:42
Victor,
That makes a lot of sense, I'll build the other kit up and try without the RF amp. I do note a lot of radiated noise comes out of the DDS board. The actual RF output is quite clean, but the near-field of the chip can be sniffed and has lots of noise. I think I'll have to shield the DDS board itself to get the best noise floor.
The scalar network analyser is still work in process, I am adding an LCD display and rotary encoder to it so it can be used stand-alone as well as controlled from the PC via serial. So far the code is fitting in a tiny861.
Regards,
Alan
7th February 2010 10:14
Hi,
I have built a stand alone scalar network analyzer similar to the one you use. I decided to use the DDS60 without the output RF amplifier because it is this amplifier that generates the harmonics. The DDS itself has harmonics level equal to its spurs level. What I did is a trade-off of spectral purity with the price of using lower output level at the DDS60 board .
I have changed the power meter input circuit to minimal loss by connecting 50 Ohm parallel resistor at input and then direct connection to AD8307 input through 100nF capacitor. I am very satisfied with the results.
Victor - 4Z4ME
27th September 2010 11:41
qrp-gaijin wrote...