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Author Topic: Best Antenna for Crystal Set Worked All States BC challenge?  (Read 35411 times)
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Tom WA3KLR
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« Reply #75 on: November 11, 2018, 03:59:21 PM »

Tom-san,

I looked at Mike’s schematic and I believe that the arrows are to show that there is magnetic coupling between the separate parallel resonant circuits.  I assume that (not having read  the page) the main on-channel coil is physically in the middle.  And that one trap is out past one end of the main coil and the other trap is out past the other end of the main coil so that they each can absorb power from the main coil at their resonant frequency, and hopefully the two trap coils are not very coupled to each other to avoid interaction as much as possible.

Audio transformers – how about trying a small 2.5/5/6.3 filament transformer, especially if one is a toroidal type?

Tommy-san
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73 de Tom WA3KLR  AMI # 77   Amplitude Modulation - a force Now and for the Future!
K1JJ
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« Reply #76 on: November 11, 2018, 04:41:00 PM »

OK, it appears the traps simply absorb energy at their resonant freq and don't pass it on to the detector.

I imagine when tuning in a station with side QRM, it's just a matter of adjusting the trap knobs for the best S/N.  Whatever it takes to pull out the station.

Nico, from what you said, is adding a BP filter to the set a bad idea because it will not be the same Q as the others?  I was thinking of adding one (same loose coupling) based on how well the Moon River radio worked.  This would make SIX adjustable tuned circuits.... 2 ganged in the ant tuner, 2 traps, 1 detector and 1 BP.

Add in the loop antenna nulling on freq and it sounds like quite a radio.   I decided to keep it fully "no-external power."   1N34A, all tuned circuits, headphones, etc.


T
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« Reply #77 on: November 11, 2018, 06:06:54 PM »

No Tom
it isn't a bad idea, just an other approach to suppress adjacent channel interference. What is done is couple much less than KxQ=1, a much too loose coupling. In order to tighten the coupling the tuned circuit has been put in between the two very loose coupled circuits. That tightens the coupling, but ONLY if the extra circuit resonates at the same frequency. But if you want a nice pass band, this method will not be the best and difficult to adjust. If adjusted well, it will give more selectivity at cost of high frequencies in the audio and will be less effective than a nothch circuit to suppress interference of adjacent channels. In addition, if will give a little more attenuation, every resonance circuit gives losses.
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K1JJ
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« Reply #78 on: November 11, 2018, 11:54:26 PM »

Tommy-san:  The 6V to 120V transformer would probably work impedance-wise.  Though I found a 100K to 750 ohm mic input transformer that will be FB for the job.  The 100K side goes across the diode and tuned circuit to keep the Q high so the headphones do not load it.  

Nico:  OK on the disadvantages of using the traps.

You mentioned that a notch filter might be better.  Is there a notch circuit that is passive, loosely coupled and simple like the BP or trap circuits?  

I'm just slowly accumulating parts and zeroing in to what I want to do.

T

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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

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There's nothing like an old dog.
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« Reply #79 on: November 12, 2018, 08:38:32 AM »

Hi Tom
The traps are notch filters, by tuning the trap you can notch a disturbing signal. So the design with the two traps of Mike Tuggle seems very effective to me.
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K1JJ
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« Reply #80 on: November 12, 2018, 02:36:06 PM »

Hi Tom
The traps are notch filters, by tuning the trap you can notch a disturbing signal. So the design with the two traps of Mike Tuggle seems very effective to me.

Got it now... will do - thanks!
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

Wise Words : "I'm as old as I've ever been... and I'm as young as I'll ever be."

There's nothing like an old dog.
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