[Central-Electronics] "Huffed and Puffed" my VFO with X-Lock 2.0

[Bill Kirkland]

Any measurements on the phase noise/spurious of the conditioned VFO
e.g. before and after ?


>From: Jim Candela <jcandela at prodigy.net>
>To: central-electronics at mailman.qth.net
>Subject: [Central-Electronics] "Huffed and Puffed" my VFO with X-Lock 2.0
>Date: Tue, 12 Feb 2008 11:42:53 -0800 (PST)
>
>This VFO is used on my CE 20A transmitter, and the H&P technique might be 
>modified to try out on the 100V/200V, and BC-458 VFO's...
>Hi all,
>
>    I have been playing with "Huff and Puff VFO" circuitry for some time
>  now, and more recently I have  purchased a PIC based commercial
>  product from Cumbria design in England. I purchased an inexpensive kit 
>that
>transforms my Lakeshore Band Hopper VFO drift rate to that approaching DDS
>stability.
>    See the link below for info specific to my installation:
>
>http://pages.prodigy.net/jcandela/Band%20Hopper/
>
>Cumbria design x-lock web page:
>http://www.cumbriadesigns.co.uk/x-lock.htm
>
>The band Hopper VFO runs continuously and covers 5.0-5.6 mhz.
>
>    These H&P stabilizers in general lock a VFO to a frequency band that
>  is +/- so many hz. The Cumbria PIC design I used keeps the Band Hopper
>  within +/- 10 hz, and usually much better than that. Some issues worth
>  noting are:
>
>* The VFO lock is disengaged when the drift rate exceeds 40 hz /
>  second, and then locks again in 2 seconds after the knob tuning is done. 
>This
>  can also happen when the VFO takes a jump on it's own from something
>  like a bad tube socket contact, or a large change in filament voltage.
>  With my band Hopper I needed to tighten the tube socket to tube pin
>  contacts, and regulate the filament voltage to exactly 6.0 volts DC.
>
>* A vacuum tube variation to the H&P requires adaptation of the
>  varactor tuning circuitry. I used dual 1N4005 diodes in series back 
>biased. If
>  I used a varactor diode or led as a voltage variable capacitor, the
>  peak signal level in a tube VFO would overload the diodes when they
>  avalanche. HV diodes like the 1N400x series are good for 5-30pf each at
>  about 0-10 volts back bias (max cap at min voltage).
>
>* This design is intended for VFO's that run continuously, and not ones
>  that sit idle until needed. This later category excludes VFO's in many
>  Boat Anchors. There is a variation of the H&P that acts like a
>  frequency counter and servo's the VFO to match a desired frequency. Go to
>  Google and search for "Huff and Puff VFO".
>
>Here is a link at an early H&P attempt I tried on the BC-458 VFO:
>
>http://pages.prodigy.net/jcandela/Huff%20and%20Puff%20VFO/
>
>Regards,
>Jim
>WD5JKO
>
>
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