resend after my first try bounced... 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 ______________________________________________________________ Our Main Website: http://www.amfone.net AMRadio mailing list List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:[email protected] To unsubscribe, send an email to [EMAIL PROTECTED] with the word unsubscribe in the message body.
