| Roger,
The most recent email I can find from Jim was sent to the RSGB group on 4 April 2013 and related to Rubidium Frequency Standards. It read as follows:
Dear Ken, [I don’t know who Ken was]
Provided your RX is set to receive the R4 carrier frequency, it does not
matter what the frequency display shows - all that matters is the difference
between the R4 carrier displayed on the spectrogram, and the nominally
198kHz harmonic of the 1kHz signal obtatined from dividing the 1MHz output
of the counter. Frequency errors in the RX will cause an offset in the
spectrogram frequencies, but it will be the same offset for both the off-air
signal and the reference signal.
For example, suppose you set your RX to 197kHz USB, and look at the
spectrogram around 1kHz - you might see the R4 carrier at 1005Hz. This 5Hz
offset will probably mostly be due to the RX; possibly also a contribution
from sound-card sampling rate error. If you now introduce the divided
reference signal, you might see a second trace appear at 1005.1Hz, which
would show that your local frequency standard was +0.1Hz above the nominal
198kHz, about +0.5ppm frequency error.
A small amount of RX drift does not matter much - the traces will move
around a bit on the spectrogram screen, but the frequency difference between
them will not be affected. However, rapid drift may smear out the traces, or
cause them to dissapear off the screen completely.
Cheers, Jim Moritz
73 de M0BMU
Last year I was preparing an article for CREGJ about the radio station at SAQ and emailed Jim with a view to using details of is electromechanical receiver but I did not receive a reply.
73 John F5VLF
[email protected]Researching history of RABSON, BLACKSHAW, GAUNTLETT, VERLANDER and ROBSONNE |
