I do not have a synthesized frequency generator or time mark generator
yet so for timebase calibration, I just use a function or pulse
generator paired with a reciprocal frequency or universal counter. For
analog oscilloscopes where sweep calibration will typically be 1 part
in 200 (0.5% or 5000ppm) at best, any frequency counter will be a
couple of orders of magnitude more accurate than needed.
Using a synthesized generator or time mark generator will just take
less time.
On Sat, 13 Oct 2012 18:32:17 -0000, "nielsentelecom@..."
<nielsentelecom@...> wrote:
A couple of months ago I was also looking to use WWV to calibrate my Tek 2246. I will try your method as I also have a Realistic DX160 SW rcvr. I have been able to 'beat' a signal generator against the WWV carrier using the signal strength meter only. I had been able to get it within 1 in 10 million for a few seconds. The generator is an old EICO tube type that I could adjust just by adjusting the modulation level which would just slightly shift the carrier after setting the frequency knob. But it is just not that stable. That way you are not needing to rely on the AF freq response to hear the 'beat' Besides your ear can't hear it anyway. This method is described in my US Navy basic electronics book. Back when it was done this way.
If you have not yet done it, you can change some caps on that DX160 and increase its audio frequency response considerably. You will get the 100HZ out of the WWV signal then off the audio amplifier. Beside it will sound so much better when SWLing.
Nick
--- In TekScopes@..., "amxcoder" <micoderup@...> wrote:
I have three frequency counters. Two have oven standards. They are old and
purchased from ebay. They all disagreed about what frequency was what. They all
have 10 mhz frequency oscillators. I have tried calibrating them with WWV before
and been only moderately successful. Short wave receivers simply do not produce
audio below 100 hz. I needed to get much closer than that. What I had going was
three freq counters that might be as much as 45 hz off from each other on 10
mhz.
Then I had an inspiration. I realized that at the receiver detector, there is
nothing to limit frequency response. I got out my old DX160 receiver and a
schematic. I found the diode (D3) that did the detecting. I put a scope probe on
this. I then tuned in WWV. I put a little antenna on the BNC output of the
counters 10 mhz clock. Presto, I had a hetrodyne sine wave from the detector
that gave me the clock error. I moved the counter freq adjust up and down past
the null. I had to do this to be sure I was actually finding a null. I had to
slow down the scope horizontal sweep speed a whole lot to see the resulting sine
wave. I could actually see a 1 hz sine wave. I let the oven warm up for a half
an hour. I set it for a "perfect" null. You still cannot be perfect at this. I
had my scope on DC input. I could watch the error signal drift up and down as
much a 1 hz as the oven and crystal drifted. I then set the rest of counters to
my new standard.
BTW there was no sound of this mixed signal coming out of my DX160. It was just
too low to be reproduced.
This procedure is much cheaper than sending your counter into a lab to be
calibrated and finally I can trust the readings on my frequency counters. This
is pretty important when you are trying to receive and transmit SSB. A 30 hz
error is pretty apparent when you are listening to it. One of my counters was 45
hz off at 10 mhz! Yikes.
David Hess