G'day LF Group,
I tend to agree with Jim on the complexity proposed. My thoughts are that
the question of accuracy/stability boil down to the following:-
1. TX - It doesn't matter what frequency (QRM dodging aside) the TX is on
as long as it is known accurately ( 177.540675Hz is as good as 177.500Hz as
far as a receiver is concerned) and it stays there so people know where it
is.
2. RX - It is important that the error in the frequency reference is
known so that you can translate the known TX to where it will appear in the
passband of your receiver. These days that means knowing the accuracy of
your receiver frequency reference to about +/-1Hz or better to allow you to
net the TX on, say, the 120 sec/dot screen of Argo.
All this can be done reasonably easily. I have an FRG-100 equiped with a
standard assessory TCXO whose accuracy is quoted as +/-2ppm over the
range -10 to +50 C. Taking normal shack temperatures here that translates
to better than +/- 0.5Hz at LF. I wouldn't call that high-tech.
I use a local time/frequency station on 2.5MHz (VNG) in AM mode to firstly
calibrate the soundcard on the 1000Hz standard-locked second pips. Then
I use CW mode (with BFO offset 600Hz) to calibrate the receiver. This I
convert to the LF (ppm error at LF is the same as ppm error at 2.5MHz)
absolute error. This has been made all the more easier by Alberto's
excellent Argo program which allows calibration values to be entered and
saved under different names which allows different receivers' calibrations
to be entered. Using Argo and the method I have no trouble switching on
my receiver and dialing up, say, 60kHz with my 10Hz step FRG-100 and
switching straight to 120 sec/dot mode and bang, there is the 60kHz signal
right in the middle of the screen.
For my FDK beacon project I have sent away for some PTC thermistors that are
used in Lyle's (K0LR) clever idea for stabilising temperature of the TCXO.
I bought another TCXO especially for the beacon from Yaesu (only $88 in
Australian pesos - so about $50 dollars US or less).
I find it bemusing to hear me do a "whoa" on super-fine frequency steps as
about 2 years ago I was lamenting loudly that there was no-one with the
accuracy/stability to take up some of the narrowband modes I was pushing
then (FDK and AFK). I guess we all draw the line in the sand where it
sits most comfortable with our present situation. I would say though,
given the history of these things, as we are experimenting we will keep
pushing the boundaries of the propagation medium (and our own patience) to
go for ever longer integration times - even with the arguments about real
QSOs etc. Larry's frequency micro-steps may possibly become a
"requirement" at some stage. Who knows for sure ?
73s Steve Olney (VK2ZTO/AXSO - QF56IK : Lat -33 34 07, Long +150 44 40)
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