I also wondered why they use a subharmonic rather than a harmonic. Maybe more difficult to get into injection lock?
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Could be. But because the 5th (!) subharmonic is used instead of an even one, it could be that the lock is too strong IOW affects AM and adjacent channel rejection negatively. The tube data (inter electrode caps etc.) might provide an answer.
Thanks, did you find any data re THD, AM rejection and similar issues?
Long ago I tried to use the 'H' part of the ECH81 in a similar way as the EQ80. It worked, but despite the preceding limiters the AM rejection was very bad (observed that by detuning the quadrature coil outside the IF BW).
No, sorry. I just noticed a forum discussion on the FM1000/6CS6 at radiomuseum.org.
Best regards!
Best regards!
Where did you find that they use the fifth subharmonic?
I understand they need to use a fairly high subharmonic to keep the interference at IF low (the nth harmonic distortion of an oscillator running at the nth subharmonic of the IF lies at the IF, and distortion usually decreases with the harmonic number).
The "Syntektor" diagram suggests that (maybe issue of avoiding patent payments). In the meanwhile I found a source with better explanation of the FM1000 (no subharmonics involved):
https://worldradiohistory.com/Archive-Rider/INDEX/Index-16-18.pdf
This diagram suggest that synchronized oscillators for FM demodulators were popular but no conventional tube could match the performance of the FM1000.
From https://worldradiohistory.com/Archive-FM-Magazine/Standard-FM-Handbook-Milton Sleeper.pdf
From https://worldradiohistory.com/Archive-FM-Magazine/Standard-FM-Handbook-Milton Sleeper.pdf
This schematic lacks the grid return to ground. It is ok the grid series fedd, I like it very much but the coil hasn't return to earth, possibly at the bottom of the oscillator tank.
I am actually working in restoring and modding an old Yaesu FT75B SSB tranceiver. Several bjt in the signal path has been replaced with JFET or MOSFET including the audio ouput, with a noticeable reduction in receiver's noise and upgrading selectivity and sensibility. This is brother of mine.
The FM tuner project isn't stopped. I need to buy a larger prototyping PCB but nowadays I loose my employment and living from saved $$$. Thus no unnecessary wasting them by those days.
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Good luck for you in finding a new employment as soon as possible, Osvaldo!
Best regards!
Best regards!
My look always is indirect: trying to understand the fundamentals, details come later. So after contemplation I immediately started to simulate a circuit with a PLL with VCO tuned to 1/5 of the input frequency and a quadrupler for the mixer (input sig - (4/5)X F(vco)), closing the loop of that frequency feedback PLL. Sim shows that would be great and could easily be adapted for tubes.
Wishing you success in getting new job!
Ok. Many thanks for your good wishes. I am actually very skeptic: thanks to peronism and populism we ar going from bad to worse here.
The real reason why things are going down globally was summarized here: http://web.archive.org/web/20220123143602/http://www.dieoff.com/
Discussion happened via an email group of which I was a member.
Guys, a good idea to steer clear of politics. Remember the rules. Thanks..