On Sun, 25 May 2014 21:44:14 -0400, Michael Black wrote:

On Sun, 25 May 2014, gareth wrote:

I wonder what others are building into their projects for a VFO these
days?

The PA0KLT from www.sdr-kits.net looks intriguing, and might settle all
arguments in favour of Vackar-Seiler or Franklin for some years to
come?

It depends on what you want to do. Since most people want multiple
bands, it starts making sense to shift to DDS or a synthesizer, since
since the output will be clean.

But there was a period when it was a sort of hybrid, an analog VFO
feeding a PLL, so you could change bands by a new coil for the VCO and
changing the crystal that mixed the VCO down to the frequency of the
VFO. There the output wsa on the injection frequency, unlike some rigs
at the time that mixed the VFO with crystal oscillators for the
injection frequency.

So about 1974 I was playing with that sort of PLL and found some car
radio PTOs at the local surplus tore. The mechanics taken care of, I
just had to add an oscillator to the coil. At that frequency, around
1MHz, it was nice and stable.

Then a year later, I found a bunch of Collins PTOs really cheap at a
hamfest, and bought some (though then I was talked into parting with all
but one). Those were of course tube PTOs and complete oscillators.
Those were easy to change to an FET, and since they too ran at 1 to
1.5MHz, they were nice and stable, and it required more turns of the
knob to travel the band.

Since that sort of thing needs a dial or frequency counter, that adds to
the complication, another reason to shift to a synthesizer.

On the other hand, if one was going to use a frequency counter, might as
well add the minimal circuitry for "huff and puff" to help stabilize the
VFO, and then actually run the VFO on the injection frequency. I've
never tried one, but I remember receivers being described in ham
magazines where the VFO ran above the signal frequency, and thus was
running quite high in frequency, but apparently with the "huff and puff"
was stable enough for SSB. Except that such things are fading, it's
easier to build a frequency counter now than it was in 1974, since you
can get higher densticy components even at the logic level. A 74LS390
(I think it wsa) is a dual decade counter, like two 7490s in the old
days. And a latch intended for computers are 8bits, better than the
7475 of the old days that were 4bits.

Michael

Hello Michael,

Thanks for your post, but unfortunately it's mostly landing on deaf ears.
The majority of the audience that you are addressing here don't know the
hot end of a soldering iron from the cold one and bladder control may
also be a more "pressing" issue for some (Rambozo the clown?)

You might be better off approaching other forums where there is sentient
life. UKRA smells of wee and isn't a place I'd suggest spending too much
time around. I come here for a few days and then disappear for a year or
so. It's probably an untapped psychologists paradise with the likes of
Rambozo and Channel 30 Gareth whose unhinged antics could possibly win
someone an Ignoble. And don't bring your kids.