From: Tobin Fricke on Jan 24, 7:41 pm

On Tue, 24 Jan 2006, xpyttl wrote:

Well, I suppose it depends on where OP is. Here in the middle, 10 MHz isn't
much of a problem but 15 is.

I am in Rochester, NY.

There should be no real problem in receiving WWV in NY state unless
you want to do it with a few feet of hook-up wire dangling inside
the room. For just WWV on HF, use whatever is handy for a long-
wire OUTSIDE...some #26 or #28 coil wire would work and be near-
invisible on the outside.

The sensitivity needed by your receiver depends ENTIRELY on how
much signal arrives in your area and how much of that the antenna
intercepts.


*HOWEVER*, 10 has one huge advantage -- there are very low cost uP crystals
for 10 MHz, so building even a simple reciever with a brick wall front end
isn't such a big deal, if the only frequency you care about is 10 MHz.

Yes, that is what I was thinking. Is there a simple way to do frequency
multiplication (or division) to get 2.5, 5, 15, and 20 MHz additionally,
and thus be able to switch between all of the WWV frequencies?

To make a simple superheterodyne receiver, even if just single-
conversion using a legacy 455 KHz IF, capitalize on some simple
tuning arrangements using an RF Amp, Mixer, 1 or 2 stages of IF:

1. A single set of front-end inductors, tune RF and LO with Cap.

2. Capacitor tuning using fixed+trimmers. Frequency range of
5, 10, 15 MHz selected by rotary switch has a total frequency
range of 3:1 high to low. The capacitance change ratio for
this is the square of the frequency change ratio or 9:1.

Note: In the old "communications receiver" designs, it was
typical to cover a 3:1 frequency change ratio with a "365 pFd"
variable capacitor (typically 40 to 360 pFd min. to max.).

3. If there are temperature-drift problems in the LO, just make
use of a small front-panel control to a parallel trimmer cap
on the LO tuning (added to the cap. of the LO resonant ckts).

4. In most cases, the temperature drift is negligible and one
can make do with behind-the-front-panel trimmer cap. settings
for three switch-selected frequencies. Some simple experiments
with an oven termometer and a frequency counter would let you
check out the drift versus temperature and compensate. Begin
with mostly NPO caps fixed for the LO tuning, expect a towards-
low-frequency drift, compensate with negative-temp coefficient
fixed capacitors for the NPOs. Temperature drift is highly
dependent on WHAT you build and HOW you build it.

"Brick wall front end"?

No need. WWV time-frequency service frequency allocations have a
protected 10 KHz bandwidth, protected from other modes in other
radio services. Given a typical Q of about 40 and two tuned
stages (ant to RF amp, RF amp to Mixer), the bandwidth would be
about 80 KHz (5 MHz) to 250 KHz (15 MHz) in the front-end. With
an IF of 455 KHz, the image frequency would be 910 KHz away.

WWV is AM, not SSB, and most probably will be used to zero-beat
external CW frequency sources that are going to be calibrated.

For those who want "extreme accuracy" in time, just compare the
time-ticks to a 1 Hz (divided down from standard to be checked)
local tick. That was the way things were done with the old
General Radio primary standards equipment circa 1950-1960, good
to 1 part per million accuracy without sweat.


Personally, I'd go with a DC rather than a regen - a lot simpler and these
days, a simple SA612 will give you way more sensitivity than you can
possibly use on 10 MHz for a couple bucks.
Heck, if the local QRM isn't too strong, I bet a 10 MHz uP crystal, a
612 and an audio amp (like a 386 or so) is all you would need.

That sounds great.

If all that is wanted is SIMPLICITY, just use any old SW BC or
wide-tuning-range HF receiver. [suggested by another]

You can convert an old "All-American-Five" AM BC receiver to
receive 5 to 15 MHz just by substituting the "coils" (inductors
is the proper word now). Substitute an inductor for the old
loop or loopstick...with a primary link for an external antenna.
[I did this many, many years ago...it works] It won't be "top
of the line" in performance, but then a regen isn't that either.
The IF can be aligned easily and the new front-end alignment
is fairly easy.

The old Hallicrafters S-38 four-band "starter" receiver that
many used was really a simple "All-American-Five" Mixer-Single IF-
AM detector-Audio Output arrangement with an added BFO. A BFO
isn't needed to beat a local frequency standard with WWV.

Assuming an original 45 pFd, 101 pFd, 405 pFd capacitance (which
includes the stray circuit capacity) to tune 15, 10, 5 MHz, a
2.5 uHy inductance will do the job. A trimmable inductor would
be best there. The first task is to check the inductor
substitutions with the existing variable capacitor. If that works,
the variable can be substituted by a switched trimmable capacitor
to avoid the knob-twisting for three HF selections...or two, or
none at all assuming fixed tuning to 10 MHz.

An old tube AM BC receiver relegated to the basement/garage
junkpile is a good candidate for this kind of thing. Tube type
radios are a bit easier to work with if you aren't acquainted
with newer solid-state circuitry. Those are certainly cheap. :-)

A converted "All-American-Five" will NOT have great sensitivity.
But, since tubes' stage gains are essentially transconductance x
load impedance, the individual gain stages can be optimized by
going for minimum-C in resonant circuits. Not that easy with
old transistor radios having individual transistor stages...those
needing fussing about with matching input-output impedances.

A friend of mine did an article on a simple WWV reciever for QRP Homebrewer
recently, issue #5 I think. He was more interested in the frequency
standard than hearing the sounds, so his contribution was recognizing the
zero beat, but still an interesting article if you can find a copy.

I don't see any articles on WWV receivers there... Does anything look
familiar: http://www.njqrp.org/data/qrp_homebrewer.html

Depends on WHAT EXACTLY you are striving for and your own
experience-knowledge. If you are a relative beginner (we all
were once), then I'd suggest converting an old tube type BC
receiver. That avoids the construction hassle and concentrates
on individual theory areas during conversion. It's the least
expensive route if using an old BC junker receiver. Individual-
area concentration can teach more about those areas than building
a pre-designed kit or magazine article project.