Oscillator Insulation

[KD3CN]

Hello Gents,

I just finished a new oscillator for a new VFO.  It's contained in a sturdy AL box, about 6X7X2".  In the past I've had trouble with stability with my old VFO, which I've attributed to the 52 degf temp in my shack in winter (I like it cold  ).  I'm thinking about insulating this new oscillator box, so that it won't be as sensitive to changes in ambient temp as the old one was.
So, I'm looking for suggestions for insulation material to encase the box.  Probably 3/8" max thickness, and locally available.  Hopefully not expensive...  Any ideas?
Thanks,  Karl  KD3CN

[WA1GFZ]

Foam works well but you will need to hold the internal temperature stable or go to temperature compensation. You could build a little controller to hold the VFO temperature at say 100F inside. Another option is to leave it turned on all the time.

[WD5JKO]

Karl,

   I have done quite a bit of work in this area. Before I go any further though I have a few questions:

1.) Is this a tube based VFO or solid state?
2.) If a tube VFO, is the filament voltage regulated?
3.) If a tube VFO, is the tube inside the box?
4.) Does the VFO oscillation stay on all the time, or is it keyed with key down or PTT?
5.) Does this VFO operate on the ham band(s), or is it outside like a 5 - 5.5 Mhz VFO?

Jim
WD5JKO

[KD3CN]

Frank,
I've always kept the old VFO powered-on 24X7, and would do likewise with this one.  Perhaps a power resistor to keep the temp stable, and an insulated box?  Given that turning on the Class E TX and sitting in the room was enough to make the old VFO drift in the past, it must have been very sensitive to ambient temp.  I like the idea of giving the new one its own temp control.  In summer months with the shack in the 60's the old VFO was MUCH more stable.

Jim,
1.) Is this a tube based VFO or solid state?   Solid state Hartley: http://www.classeradio.com/vfo_2_band.pdf
4.) Does the VFO oscillation stay on all the time, or is it keyed with key down or PTT?  The oscillator stays on all the time.  It runs on 40m, and is divided down to the operating 80m or 160m frequency, when PTT is activated.

Thanks for any ideas guys.  My VFO stability problems are definitely related to ambient temperature in the shack.  When the ambient temp goes up from the 50's to the 60's the stability problem goes away...

73, Karl

[KD3CN]

Also,  The main air-variable tuning cap is padded with 220pf of npo ceramic disc capacitors, so I also have the option of playing with temperature compensating capacitors...
73, Karl

[WD5JKO]

Karl,

   Your VFO is a natural to be stabilized with a "Huff & Puff" stabilizer. A little company in England, Cumbria Designs makes an inexpensive PIC based "Huff & Puff" stabilizer called X-Lock. A "Huff & Puff" typically moves the VFO via an ALC like control between lock points based upon a divided down crystal. The X-Lock uses a PIC based system that refines the concept and will keep your VFO within  +/- 10 Hz window once locked. The lock kicks in a few seconds after you stop turning the frequency adjust knob.

   The concept doesn't fit VFO's that are keyed, but your application seems to be a natural for this concept.

Here is the X-Lock 2.0 VFO stabilizer:
http://www.cumbriadesigns.co.uk/x-lock.htm

click on X-Lock v2.0 to download manual and schematic:
http://www.cumbriadesigns.co.uk/kits.htm


   The kit comes with an LED that can be used as a varicap diode for many solid state VFO's. The trick is to merge the X-Lock to your VFO and achieve the correct varicap tuning range over a range of about 0-8 volts DC.. This will take some work. Something like a 5 Khz shift over 0-8 volts varicap voltage will work fine.
   
   I am using the X-Lock 1.0 on a tube VFO that tunes 5 - 5.5 Mhz, and it works extremely well for me. I had to come up with a varicap diode that would work in a tube VFO. To avoid avalanche and rectification of the oscillator, I used dual 1N4007 diodes as varicaps. These power supply diodes work great as a varicap!!

   Here is what I had to do to make the X-Lock work with a Lakeshore Band Hopper VFO. I use this with my Central Electronics 20A. Now the 9 Mhz crystal in the 20A is the major source of drift.

Start with Read_Me.txt:
http://pages.prodigy.net/jcandela/Band%20Hopper/

   I also have a cold ham shack. With X-Lock, my tube VFO locks after only a few minutes turned on, and from there stays locked. I have no need for a heated box for the VFO. What I do need however is a crystal oven for the 9 Mhz crystal in my 20A.

Jim
WD5JKO

[k4kyv]

Wonder what the shipping charges are to the US.  When my wife sent a xmas gift to her sister in England a few years ago, the shipping charges were several times what the contents were worth.

And would the vco lock circuit introduce phase noise to the oscillator output.

[KD3CN]

Interesting Jim,  I'll check it out.  Thanks, Karl

[WA1GFZ]

Huff and Puff is the same method used in the HP8640B.
It would be cheaper to build a little temperature controller and feed a power resistor inside the VFO to hole the internal temperature stable. Temperature compensation caps are rare as hen's teeth. Check out the Johnson 122 VFO compensation. That is a very stable VFO. You can use a diode as a sensor and a dale power resistor as a heater element. A linear regulator like a 723 will work as a controller.

[WU2D]

How about taking an opposite approach and allowing the oscillator to be well ventilated so the device always stays close to ambient temperature, whether on or off, winter or summer. Even the most primitive VFO's, if built with good quality parts generally stay on frequency within a couple hundred Hz if they are left on all of the time.


Mike WU2D
 

[WU2D]

Frank - remember that little silver transmitter at the first Nearfest? I just "restored" this truly primitive transmitter with very little documentation on how to power or how it would key. It is a pre-WW2 set type called BC-AR-430. The very little box has band changing like a small HRO with plug in coil sets which include the master oscillator and the PA tank. It was used in the small planes we entered WW2 with, mostly in trainers and fighters. The VFO is a type 10 in an Armstrong feedback oscillator and the PA is a single ended neutralized type 10. The modulator is a pair of type 10's in parallel Heising and it is driven by a carbon mic.

Everything about this transmitter says - I am a 1929 design. But the construction and parts selection is a top notch Western Electric, Kearney NJ plant effort.

The oscillator is beautiful and it keys better than an ARC-5! You have to wonder what kind of engineers it takes to put a big bright Type 10 oscillator in a small aluminum box, running at 5 Watts, and the darn thing is stable in 2009!   

Mike WU2D
 

[WU2D]

A couple pics of this VFO

[WA1GFZ]

a work of art Mike

[K4TLJ]

Wonder what the shipping charges are to the US.  When my wife sent a xmas gift to her sister in England a few years ago, the shipping charges were several times what the contents were worth.

And would the vco lock circuit introduce phase noise to the oscillator output.

I recently bought two XLock kits. With shipping the total cost was $71.00. I recall the kits cost 19 pounds each. So cost varies with the daily exchange rate.

I put one kit in my Swan 700CX. Amazing! A Swan that stays within 10 Hz of the dialed frequency indefinitely. As to phase noise I don't have the test equipment to measure it but since the tuning is done VERY slowly with a varicap I don't see a problem. The XLock cannot correct sudden frequency shifts such as would be caused by bad wafer switch contacts or vibration. As Cumbria says' The XLock will make a good VFO great but cannot make a poor VFO good.'

I ran the control voltage for the LED in a mini coax and used an adjustable piston cap for the coupling cap. Since the caps in the Colpitts oscillator are not easily accesible I paralleled the control capacitor with the VFO tuning cap. The correct coupling turned out to be six pF for about two KHz control.

[WD5JKO]

Terry,

    I am glad that your experience with X-Lock was good. I'm glad that you pointed out the limitations too such that x-Lock won't make a crummy VFO great. The X-Lock was designed by Ron Taylor, G4GXO. The post below on Hans Summer's web site goes over the development of the X-Lock:

http://downloads.hanssummers.com/ttfeb07.pdf

Hans also has a very comprehensive compilation of the "Huff & Puff" VFO:

http://www.hanssummers.com/radio/huffpuff/index.htm

There is also a "Huff & Puff" Yahoo Group.

    I have an early X-Lock kit. I corresponded quite a bit with Ron Taylor via email, and boy he takes the time to answer emails. In fact he started the dialog by asking me how my X-Lock installation went after he realized that the PDF manual had a typo in it. This has since been corrected.

    My main issue was/is that the VFO locks while I am still tuning. This means it is tough to get the frequency closer than 30 hz to the target, say 3870.03 instead of 3870.00. Soon after corresponding with Ron about this he reprogrammed the PIC to allow longer tuning time default, and user programmable tuning time. It is neat that you can slowly (like drift) turn the frequency knob on the VFO and the frequency stays constant until you run out of varactor diode tuning voltage range. This is like AFC on a FM broadcast tuner.

    Once you go X-Lock you don't go back. Gone are the 100's of hours trying to tediously play with temperature compensation ratio's, and then another logging of freq versus time over another temperature cycle of the VFO.

    For those that rather "spin their own" H&P stabilizer, Hans Summers site has many examples where a few dollars of digital IC's and a wrist watch crystal will make a H&P. Keep in mind that virtually NONE of these will H&P within 10Hz, but instead H&P within 64Hz or 128Hz. Sure, this is good enough for AM, but with SSB today you will hear, "Hey OM, your drifting out of the band"!

    One problem with the simple H&P circuits is that the digital circuitry controls the analog varactor tuning voltage. As a result, the tuning voltage is likely to be modulated such that the carrier is "raspy", or no longer a 'T9' note. With X-Lock, Ron goes through great pains to eliminate this effect. He uses opto-couplers between the digital and analog circuitry, and separate power supplies.

Jim
WD5JKO