[AMRadio] Re:Resonant Choke, AM activity in the expanded band

D. Chester k4kyv at charter.net
Fri Feb 16 16:09:56 EST 2007

> One passing remark I wondered about while reading this essay is whether it
> was feasible to stick with the stock 10 Henry choke, and resonate it to 
> 120
> hz with a suitable oil type capacitor with a value somewhere around 0.15 
> uf
> @ 5 KV. (10H || with 0.15 uf = ~ 130 Hz resonance). I have limited
> experience with this approach, but the one time I tried it, it seemed that
> the critical inductance need dropped leaving everything else constant, and
> the AC ripple coming out of the filter was far less than a normal choke
> input filter. I did not do dynamic load variation tests however, so who
> knows..

The main problem with the resonant choke is getting a suitable resonating 
capacitor.  It has to be rated at high voltage, and usually is well under 1 
mfd, and the value is critical, dependent on the inductance of the choke at 
full load.  A resonant choke works as well as or better than a regular choke 
input filter that uses a choke of optimum inductance.

>> Is it just me, or is the AM activity in the new voice territory
>> declining
>> already?
>> Mike Duke, K5XU

>Kc5mip I think A.M. is well and everyone seem to be
> hanging on 3880 around 7.30 a.m. in the mornings

That's exactly what I predicted the day the band opened.  There would be an 
initial rush to the new frequencies, but as soon as the new would wear off, 
everyone would migrate back to the old frequencies and same old QRM.

I make it a point to call CQ in the new segment if I don't hear any AM 
activity.  Look for me around 3650, 3685,  3725,  or wherever there is a 
clear spot, anywhere between 3600 and 3775.  Some SSB "dead air" groups are 
already trying to claim certain frequencies and run anyone else off who 
comes near, even if no-one in their group has transmitted within the past 

Don k4kyv

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