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 Post subject: A good VFO stabilizer for your boatanchor
PostPosted: Aug Sun 30, 2009 2:57 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2833
Location: Powder Springs,Ga. USA
I bought this VFO stabilizer from Cumbria Designs in the UK. http://www.cumbriadesigns.co.uk/x-lock.htm

I installed the completed kit in my Swan 700CX and was very pleased. It will hold the VFO frequency within ten Hertz indefinitely. The only 'problem' was determining the optimum coupling capacitance from the varactor to the VFO tuned circuit. The value is approximately 6 pF. I used an adjustable 2-12 pF capacitor that I had bought in a grab bag of parts forty years ago.
Cumbria uses a back biased red LED for the tuning element and it works very well.
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PostPosted: Aug Sun 30, 2009 4:40 am 
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Location: Monterey California USA
Interesting. Someone in the USA was making one at one time a few years ago.

This might end the tyranny of the drifting Hammarlund HQ-170A VFO for me once and for all, but the creator says it "won't make a bad oscillator into a good one." :)

It's cheap enough to get several of them.

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PostPosted: Aug Sun 30, 2009 5:33 am 
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Location: Powder Springs,Ga. USA
Geoff Fors wrote:
Interesting. Someone in the USA was making one at one time a few years ago.

This might end the tyranny of the drifting Hammarlund HQ-170A VFO for me once and for all, but the creator says it "won't make a bad oscillator into a good one." :)

It's cheap enough to get several of them.


Yes, Phil K4DPK, makes one but charges $70.00. I paid 25 pounds for the Cumbria Designs kit which became $42.00 with exchange and shipping. Cumbria has reduced the price since I ordered and improved the design a bit.

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PostPosted: Aug Sun 30, 2009 2:27 pm 
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Ham Radio Magazine ran a few simple Huff'n'Puff stabilizers back in the 70s, for anyone who wants to perfboard one... I always wanted to try one, but my understanding is that they have limits on the rate and amount of drift they can lock to? The newer desigins have the same lock range and other limitations?

Pete k1zjh


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PostPosted: Aug Sun 30, 2009 3:05 pm 
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Location: Southern NH, 03076
While its a lost cause to try and stabilize some radios there are a few basic steps to take on the better ones.

Regulated DC filaments.

Zener regulated screen and plates.

Just the small filament variation on AC will cause instability, thus the 4H4 and other ballast stabilizers of old usually replaced with a 6V6.

A VR tube is far from stable. Even NIB ones are suspect and have to be carefully checked. A 5W zener is around .25 these days. Do it to the BFO also.

Some radios run the LO with high B+. If you dont mind a mod, drop it to 75-90V and install a buffer underneath for full mixer injection and kill two problems at once.

As mentioned too many times to count, use a bucking transformer to reduce heat. An old timers trick was to prop up the cabinet lid a bit.

Carl


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PostPosted: Aug Sun 30, 2009 3:24 pm 
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Location: Powder Springs,Ga. USA
Peter Bertini wrote:
Ham Radio Magazine ran a few simple Huff'n'Puff stabilizers back in the 70s, for anyone who wants to perfboard one... I always wanted to try one, but my understanding is that they have limits on the rate and amount of drift they can lock to? The newer desigins have the same lock range and other limitations?

Pete k1zjh

Cambria suggests to pick a coupling cap that allows +-20KHz control. Since the SWAN is single conversion and the local oscillator has a very wide range I selected a coupling cap that allowed stable control on 80 meters yet kept the range on the higher bands within reason. If too high value coupling cap is used a 'warbling' effect can be heard as the correction is made every 100 milliseconds.

Their design is fairly sophisticated in that it uses microprocessor control and optoisolation to prevent digital artifacts in the control voltage. The control voltage starts at four volts and can range +- three and a half volts or so. The board has two regulators, a five volt for the digital section and an eight volt for the analog. They use a high quality double sided board with plated through holes. The assembly instructions are good and are somewhat in the Heathkit style.

I installed the circuit in a way that easy removal could be done just in case I or someone in the future wanted to go back to the drifty past. :)

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 Post subject: Re: A good VFO stabilizer for your boatanchor
PostPosted: May Tue 21, 2019 6:05 pm 
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Joined: May Wed 07, 2014 1:39 am
Posts: 24
Bringing back an OLD thread -- but hoping that someone might remember...

I'm trying to add a VFO stabilizer to my Swan VFO. The thread speaks to adding one to a 700 -- can anyone tell me exactly where (and how) the control voltage was added to the Swan VFO? I've already got the working X-Lock in the rig and picking up VFO output -- just need to know where to insert the varactor.

Thanks!

Jeff
WB3JIH


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 Post subject: Re: A good VFO stabilizer for your boatanchor
PostPosted: May Tue 21, 2019 11:48 pm 
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Joined: Jun Mon 22, 2015 6:21 pm
Posts: 372
Location: Bath, Maine 04530
Does the Swan have RIT? I have done two Kenwood VFOs and connected the X-Lock output directly to the RIT line. NO Diode was added. Work great. FWIW Carl

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 Post subject: Re: A good VFO stabilizer for your boatanchor
PostPosted: May Wed 22, 2019 12:05 am 
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Joined: Oct Sun 04, 2015 8:22 pm
Posts: 81
Location: Newton, MA 02465
Jeff -

You might find the following thread:

https://groups.io/g/QRPLabs/topic/30925887

to be of interest. The frequency stabilization component of some of QRP Labs devices
use Huff & Puff (mind you, my technical know-how is such that I can barely follow the
thread) and a question came up about packaging that component as a stand-alone for
use in stabilizing vintage VFOs. Some interesting comments there about the issues
involved.

73 -

Bruce K1FFX


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 Post subject: Re: A good VFO stabilizer for your boatanchor
PostPosted: May Wed 22, 2019 3:13 pm 
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Joined: Jan Sat 12, 2008 12:25 am
Posts: 148
Location: Kingwood, Texas
Try connecting it directly across the tuning capacitor. I’ve installed them in a couple of Swans and that worked fine. You’ll have to adjust the alignment after it’s installed.


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 Post subject: Re: A good VFO stabilizer for your boatanchor
PostPosted: May Wed 22, 2019 5:31 pm 
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That may give the Huff n Puff too much authority. Best to use a little coupling as possible. The cathode of a Collpitts might be a good place to start. You need to correct for only a few kHz, not tens of kHz drift.

Pete

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 Post subject: Re: A good VFO stabilizer for your boatanchor
PostPosted: May Wed 22, 2019 7:58 pm 
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Joined: Jan Sat 12, 2008 12:25 am
Posts: 148
Location: Kingwood, Texas
Peter Bertini wrote:
That may give the Huff n Puff too much authority. Best to use a little coupling as possible. The cathode of a Collpitts might be a good place to start. You need to correct for only a few kHz, not tens of kHz drift.

Pete


You adjust the value of the series capacitor to limit the swing. In the case of the Swans, generally 1-2 pF will be about right.

Darrell


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 Post subject: Re: A good VFO stabilizer for your boatanchor
PostPosted: May Thu 23, 2019 12:04 am 
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Location: Somers, CT
Agree with that...

Pete

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 Post subject: Re: A good VFO stabilizer for your boatanchor
PostPosted: May Fri 24, 2019 3:24 am 
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Joined: May Wed 07, 2014 1:39 am
Posts: 24
Thanks for the assistance!

I ended up installing the varactor inside the VFO compartment, and coupled it with a 2.54 pf SM to the tuning capacitor. That seems to have gotten it, but as someone said, I definitely have to realign the vfo...

The rig is actually a Swan 600R -- stand alone receiver. It has an exotic tuning control -- a broad band tuning setting, then a 200 KHz range on the main dial. Easy to accommodate for the additional capacitance, so all good.

The rigs now in action:

Image


73 all!

Jeff
WB3JIH


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