[ARC5] Subject: Re: Easy selectivity improvement.

[Fuqua, Bill L]

  The wobulator originally was a coneless speaker using the voice coil to
move a one plate (flat disk) of a capacitor. They were used in some FM exciters and also
in sweep generators. For a while sweep generators were still called wobulators  after they
started using other means of modulating the frequency. In fact even at up until the mid
1980's the term wobulator was used in some Polish to English Translation dictionaries.
I found this out when a physics graduate student came to our lab asking for one. The other
guys had no idea what he was talking about but I said "sure we have one".
   The first radio altimeter used in WWII used a wabulator and a pair of push pull 955's in the
oscillator. 
   Another way to produce FM is to remove the shield from a powder iron or ferrite tuned oscillator
transformer, wrap some wire around it and modulate the current thru the coil, naturally it will require DC bias
current.
  73
Bill wa4lav

________________________________________
From: arc5-bounces at mailman.qth.net [arc5-bounces at mailman.qth.net] on behalf of J. Forster [jfor at quikus.com]
Sent: Friday, May 10, 2013 9:28 AM
To: Fred Cousins
Cc: arc5 at mailman.qth.net
Subject: Re: [ARC5] Subject: Re:  Easy selectivity improvement.

If you have an old RF signal generator it is relatively easy to add a
'wobulator' - a small speaker turned into an audio frequency driven
variable capacitor- to turn it into a narrow range sweeper.

These days, adding a variacap to an RF generator is nearly trivial, All
you need is a back-biased signal diode as a varicap (or a real one...
they are cheap), a coupling cap, and a couple of resistors and an source
of sweep waveform.

It'd be a trivial retrofit for some kit-built RF generators.

-John

===============



> There is a specific sweeper circuit for viewing IF curves on a scope was
>  called a "Wobbulator"  the British vintage radio magazine "Radio Bygones'
> No. 82 April/May 2003"   featured a updated advanced model - If you search
> for it - you will find a copy of it on the net.
>
> A UK glowbug that goes by the moniker "AndyDaviesByTheSea" on You Tube has
> a nice demonstration of the unit in action - he credit the
> units usefulness in one of video in getting a grossly misaligned
> Eddystone
> communications receiver  back on track.   Try Videos   44- 48
>
>
> Fred Cousins
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