RadioBanter - View Single Post

April 3rd 06, 02:00 AM posted to rec.radio.amateur.homebrew

On 1 Apr 2006 15:55:06 -0800, wrote:

Using those old verniers is risky to me only because finding
replacements if they start to slip or have backlash. I at least try to
find or build something I can replace. But the Eddiestone are just so
nice looking.
Well, maybe this one WILL be nice looking

What I did on the HP VFO was like in fig 7.27 EMRFD. The output of the
IC is a square wave. I was concerned after I looked at the output on my
analyzer. I see why the cmos marker generators are so popular. Strong
harmonics way above 100MHz. The output was significantly cleaner from
the tap. Right around then I decided to go back and finish my SSB
receiver and mount it in the chassis so I didn't have to use so many
clip leads while I was playing with it.
Figure 7.27? I don't quite follow that, unless you're talking about
how you've band-switched it.

I was going to do something similar to the fig 12.25 mixing type LO and
I still may. My original receiver had a 9MHz filter but a relatively
strong birdy from the LO at 7.2MHz. I decided to just change the filter
to 9.216MHz and no birdies. Was hell trying to find closely matched
9.216MHz crystals though. I got 65 ea from Mouser and only got ten
within 5%. Mostly a wide discrepancy in ESR. I guess you can make up
for a lossy filter but after spending as much time as I did on both
filters in measuring crystals I wanted something to show for it.
I'm using that design because I'll need 2 HFO's in two separate rigs
I'm working on. That one is interesting because of the 5 MHz output,
but I won't be using that for the rig itself. I'm using a 74HC4053
switch to mix either of two LOs with the 5 MHz VFO. The transceiver
I'm using EMRFD circuits for is a 15 and 20 meter SSB/CW traansceiver.
I'm using a 9MHz If, with HFO frequencies of 25 and 18 MHz. I'll use
the sums to produce the correct LO frequencies.

The other rig is one I've been working on, off and on, for over a
year. That one is based on G4GXOs Belthorn SSB/IF module. I picked
an IF of 11 MHz for it, because 32 and 25 MHz HFO crystals will allow
me to use a VFO of the toal span of 3.890 4.148 MHz. All of the
crystals are Mouser 39-cent variety.

I didn't realize it, but when I put in my order from Digi-Key last
wee, I stumbled across the ECS 18 MHz crystal, a value I didn't have
in my data base of available frequencies...that allows me to make the
EMRFD rig a 2-bander, adding 20 meters!

I was going to try the control circuit on the tap in my HP VFO. I know
it will work thiough even though I haven't tried it. Its just getting
the correct link and varactor. The fast HP VFO's still amazes me.
I get started on too many things so I went back to my SSB rig.

On the inductor drift I agree. I seem to have luck with slightly lower
L and using the slight neg temp coefficient of the COG caps. I did that
in my tube receiver built with toroids. I ended up using a small silver
mica for temp compensation of all things. Like you I look at other
circuits and copy. I didn't on this VFO because I was copying my own
circuit that worked before from something I am sure I copied. The more
I try other things though the less I copy. Right now I am working on a
25 VDC 6AMP power supply for the transceiver. I am going to try power
mosfets again as I had good luck in the last low power linear I built.
I am only looking for 40W or so. Plenty big for the type of SSB I will
work. I have a 28 VDC 3 A supply I made years ago. Just not sure it is
big enough for the PA I am going to use. Its not that efficient.

Gosh, typo errors in ham publications! Hard to believe! Not!. Good for
you for checking. I have a mess of spreadsheets with most of the common
formulas. I also made some for double and triple tuned BP filters,
feedback amps, my LC meter calculations, a logarithmic power meter and
crystal parameter testing. I check a lot of circuits in books by
plugging in the data to my sheets.

EMRFD is a great book. One thing I have been using in my transceiver LO
now is the hybrid splitter shown in fig 6.75. The vfo in 12.25 shows a
resistive version. I used the hybrid on both my VFO and BFO. That is a
nice technique even if it is a few more parts. I guess Wes must be a
better Numptie than all of us?
I'm not sure I really knew much of anything until I got EMRFD. The
first few weeks, I had a running stream of Q&A emails with Wes, and he
was kind enough to be patient and explain some things. One in
particular was a problem I had in adapting a published L-network to
the actual impedances of my crystal filter in the 30 meter rig I built
for Straight Key Night .

In Fig. 12.25, he's actually using the take-off point from the VFO to
the mixer from the attenuator pad for the 5 MHz output, to get the -10
dBm for 5 MHz for the 20 meter part of the rig.

I bet you will really enjoy experimenting with the fast HP VFO. I
haven't had that much fun with a simple project in a long time. Once
you build a few you start getting alot of ideas on how to use it. Then
it starts adding to your list of projects. You start losing sleep, the
wife keeps asking you to take the trash out, you stop shaving, grow
your hair long and start smoking and drinking too much coffee. Then you
are in Nugatory. Thats ham purgatory. My wife calls it the doghouse.
Sleep? What's that? Fortunately, my wife is busy getting her business
up and running, and I have plenty of time on my hands (I've inherited
the dog and cat-tending responsibilities).

Maybe I will put a picture of my progress on the SSB transceiver on the
tech site soon. I never know what Chuck is willing to accept though. So
I get a little cautious.
I understand completely. However, why not start a folder anyway?
There's only a couple of them there, and it's not like it's stuff that
belongs in the Smithsonian. Now if Dale had his receiver on the site,
that's certainly Smithsonian-quality!

When I was building the SKN Special, I did running updates to the NoGa
list with the latest photos on my web site. Now that it's finished, I
recently went back and reorganized that page to reflect past tense.
One of the highlights was definitely getting the VFO going. On the
scope, the signal has a weird distortion in the sine wave, like the
trailing edge is partially scooped out; I should post that on the
yahoo group site and see if anyone can figure out what it means. But,
since it's feeding an NE602, and they can take square waves, I guess a
little distortion doesn't matter.

Keep me up on your progress.
Tomorrow, I lash up a test capacitance circuit. Then, once I can
finally do the math and figure out which variable I can use, I'll
start building. the Digi-Key prts for the Huff and Puff whould be
here mid-week.

72/73,
Ted KX4OM