[GreenKeys] CRT Question

[Lester Veenstra]

As the model L was my first TU, I must say I never had any problems in
tuning. It may well be that the ear was part of the AFC feedback loop.

By the way, speaking of AFC loops, anyone want a CV-116?


Lester B Veenstra  MØYCM K1YCM W8YCM
lester at veenstras.com

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-----Original Message-----
From: Jim Haynes [mailto:jhhaynes at earthlink.net] 
Sent: Friday, August 21, 2015 10:46 AM
To: Lester Veenstra
Cc: greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] CRT Question

On Fri, 21 Aug 2015, Lester Veenstra wrote:

> In the Altronics Howard Model L they took the channel filter (Mark and
space
> filters) and passed them to a dual channel amplifier, driving the
> oscilloscope plates, However, across the plates were an additional high q
> tank (the usual 88 mhy torroid based). Since this was a very high
impedance
> point (the scope defection plates), the high Q allowed a very narrow
> bandwidth. Therefore, instead of the usual sloppy bananas tuning display,
he
> was able to present a clean crossed line display that allowed unambiguous
> tuning.
>
This kind of thing can be overdone.  With simple tuned circuits you get
crossed bananas (or an airplane) and you can tell which direction you need
to tune if you are off frequency a little.  The Electrocom 440 model
uses signal strength in the channel filters to modulate the amplitude
of the signal sent to the scope.  The result is a perfectly sharp cross -
but if you are off frequency the arms of the cross get shorter but you
don't know which way to turn the tuning to correct the problem.