21-06-2012, 08:24 PM
As always Al. thanks for that you're keeping me going! your initial thoughts on that last idea I posted run similar to mine but I thought I would throw it open for comment.
It's been piddling down all day today so I spent the day at the Regenerodyne bench, I hooked up the output from that 500Khz Xtal marker in the B40D again and fed it to the grid of a triode, the triode does not have a particular high Gm, nevertheless I made up a tank circuit for the anode load the fed it's junction via a capacitor to the grid of the mixer, I have tried this before but I took a bit more care this time, the results were reasonably encouraging, although I could not get much out of it much above the 20th harmonic, at the 20th harmonic (10 Mhz) I peaked the tank and set the RF tune to the 40 meter slot, it worked quite well although the mixer conversion gain seemed to be down which was kind of expected. The reason I mention this is that if I can get that with a 1 Mhz xtal job then that might take the HG source up to 20 Mhz which will be two thirds of the way there....
I then substituted the Xtal marker input with the sig gen at 10 Mhz (for 40 meter coverage) and the gain shot up considerably once the triodes tank had been tuned, unfortunately I have no 'scope or means to measure RF which is a pain.
I also tried a short while ago setting the sig gen to 17 Mhz (for 20 meter coverage) using the same arrangement and proceedure, the results were equally as good. I also tried resetting the sig gen to half frequency in both instances but tuning the tank at double the half frequency this worked well, the gain as best as I can ascertain being only marginally down.
So in short, amplifying the output from the sig gen then tuning that amplifiers anode tank circuit to the sig gen frequency increases the Mixer gain, this is to be expected as normally mixer grids have several volts on them as opossed to the 200 mv I previously had (un amplified, I also noticed that certain unwanted hetrodynes disappear by using this method but I guess that is to be expected also as we are cleaning up the sig gens output..
Of course all this is fine but I need to try out the HG idea with some decent valves/ components before knowing which path to take..I have still yet to order them!
If I have to go some other route then one way could be a VFO say for general broadcast transmission tuning and a few switched Xtals for the Amatur bands for that extra stabilty.
I might even put it all together properly and use the sig gen, it would make a nice compact receiver.
I have also rewound the RF tuning coils which has resulted in improved tracking between them, the RF tune peaks up really well now on 20 meteres with a nice sharp peak, a reduction drive will not be required on the RF tune just a decent size control knob say 2 " diameter with a calibrated skirt or pointer.
If anyone is thinking of building a Regen for SWL then I would certainly recomend the RF amp-Mixer-Tunable Det- A/F Output route which is basically what the Regenerodyne is.
Lawrence.
It's been piddling down all day today so I spent the day at the Regenerodyne bench, I hooked up the output from that 500Khz Xtal marker in the B40D again and fed it to the grid of a triode, the triode does not have a particular high Gm, nevertheless I made up a tank circuit for the anode load the fed it's junction via a capacitor to the grid of the mixer, I have tried this before but I took a bit more care this time, the results were reasonably encouraging, although I could not get much out of it much above the 20th harmonic, at the 20th harmonic (10 Mhz) I peaked the tank and set the RF tune to the 40 meter slot, it worked quite well although the mixer conversion gain seemed to be down which was kind of expected. The reason I mention this is that if I can get that with a 1 Mhz xtal job then that might take the HG source up to 20 Mhz which will be two thirds of the way there....
I then substituted the Xtal marker input with the sig gen at 10 Mhz (for 40 meter coverage) and the gain shot up considerably once the triodes tank had been tuned, unfortunately I have no 'scope or means to measure RF which is a pain.
I also tried a short while ago setting the sig gen to 17 Mhz (for 20 meter coverage) using the same arrangement and proceedure, the results were equally as good. I also tried resetting the sig gen to half frequency in both instances but tuning the tank at double the half frequency this worked well, the gain as best as I can ascertain being only marginally down.
So in short, amplifying the output from the sig gen then tuning that amplifiers anode tank circuit to the sig gen frequency increases the Mixer gain, this is to be expected as normally mixer grids have several volts on them as opossed to the 200 mv I previously had (un amplified, I also noticed that certain unwanted hetrodynes disappear by using this method but I guess that is to be expected also as we are cleaning up the sig gens output..
Of course all this is fine but I need to try out the HG idea with some decent valves/ components before knowing which path to take..I have still yet to order them!
If I have to go some other route then one way could be a VFO say for general broadcast transmission tuning and a few switched Xtals for the Amatur bands for that extra stabilty.
I might even put it all together properly and use the sig gen, it would make a nice compact receiver.
I have also rewound the RF tuning coils which has resulted in improved tracking between them, the RF tune peaks up really well now on 20 meteres with a nice sharp peak, a reduction drive will not be required on the RF tune just a decent size control knob say 2 " diameter with a calibrated skirt or pointer.
If anyone is thinking of building a Regen for SWL then I would certainly recomend the RF amp-Mixer-Tunable Det- A/F Output route which is basically what the Regenerodyne is.
Lawrence.
