[Milsurplus] BC-9: Back to Head Scratching.

[Bill Cromwell]

Hi Dave,

I have seen that 'antenna effect' called 'suckout' and 'dead spots'. An 
RF amp or mixer ahead of the detector, among other things, eliminates 
that by isolating the detector from the antenna. That is not a 
suggestion to add an rf stage. Just sayin'

73,

Bill  KU8H

On 02/18/2017 07:18 AM, David Stinson wrote:
> Well, I'm flummuxed again.
> No matter what "frequency compensation" cap
> I use, I can't seem to net the thing closer
> than about 3 KC.  Going below about 220 pFd
> actually makes it *worse.*  Duh......
>
> I'm beginning to wonder about the silver micas
> in my junkbox.  They test OK on the ZM-11.
> And there is an "antenna effect" when using the tank-and-link output.  
> I haven't defined it yet.
> Maybe it's the triode-connected 6AQ5.  Maybe
> there's just a limit due to its quirks.  None
> of the other tubes I've tried work on receive
> nearly as well and some, not at all.  I even
> plugged-in a VT-25A.  Good on transmit,
> but no will regen.
> I'm going to assemble the loop this weekend
> and see how it behaves with that.  We'll see.
>
> One other thing for those thinking of tinkering
> with a "replica."  A very old bug-a-boo with regens and oscillators 
> like this:  If you use the
> link-coupled output and your antenna is resonant exactly at the freq 
> of operation, the oscillator can't handle the load and it will quit.  
> I  don't remember what this effect
> is called but it's in all the best regen literiture.
> I've been fiddling around 3550 KC.  If I use a tuner to present a flat 
> 50-Ohms to the link at 3550, when I tune the transmitter freq. it will 
> actually "jump over" the resonance area- it will tune up to about 3540 
> and then "jump" to about 3610.  I have to tune the antenna to about 
> 3525 to get it to behave.
> Even with that, I was still able to make a nice
> QSO between here and South Texas with the
> mighty 2 Watts.   (Not last night.  No chance
> with that CW contest).
>
> Mike Hanz contributed an excellent, non-destructive suggestion: Use a 
> 100-volt
> Zener, resistor and reed relay on the DC
> side of the 120 VDC line.  Switch-in a small
> Receiver compensator that will certainly, finally
> net the radio.  I mean, I'm never going to have a VT-1 to actually 
> test it under original condition,
> and I don't usually object to such "non-hacks."
> But I'm not sure I'll go that far.  I'm very pleased
> to have gotten the radio back into a condition where its preservation 
> long-term is likely.  It's still fun to play with as a receiver or as a
> transmitter using an external receiver.
> Maybe I should count myself lucky that, with the help of our 
> outstanding community of "Smart People," the radio is alive and kicking
> again after almost 100 years.  I even had the correct Hi-Z 12,000 Ohm 
> headphones.  Maybe I should "quit while ahead"
> before I screw it up good.
> Still want to see how it plays with the loop.
>
> Going to try to make a few contacts with it
> for Novice Rig Roundup (no; it's not a
> "Novice rig" but it is cool ).
> Will likely use an external receiver.  The transmit freq is still 
> surprisingly stable and chirp is minimal.  Just for fun.
>
> Have a great weekend, y'all.
> 73 Dave AB5S
>
>
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bark less - wag more