Annapolis thoughts (fwd)
Wed, 17 Feb 1999 14:23:41 +0000 (GMT)
I made it back in good order Tuesday night. On my trip I found a Harbor
Freight store and had a good look around.
I also thought about the use of Annapolis antennas. One experiment would
check signal to noise on the European LF broadcast stations using a
variety of our own efield probes, loops and the Annapolis antennas as
large aperture receiving antennas. We could have several receivers
connected to the various antennas measuring signal levels and noise
levels on quiet adjacent channels.
We can use this information to help determine if large aperture antennas can
help receive weak signals and also help to quantify system parameters needed
to establish a transatlantic circuit between amateur stations.
1. Rycom or other selective voltmeter meter readings could be used as
well as variable step attenuators and more conventional receivers. Two
keys are the dB difference between the signal and the noise and the
"equivalent" noise bandwidth of each receiver used to measure noise.
2. We need quiet background so noise is non-sferic and non-powerline and
reasonably strong broadcast signals so we are getting a true measure of
the signal. With occasional sferics we can just take a reading in
3. We need sky-wave signals to have confidence in the experiment truly
demonstrating the value of receiving antenna aperture. Aperture may not
act the same on ground wave signals.
4. At Annapolis we ought to have the most dramatic differences between
small and large aperture receiving antennas we can get. I am not sure
the antenna needs to be tuned to acheive its best or optimum "aperture".
I do have some sutiable fixed and variometer inductors to try out. Any
5. For our site survey we need to determine how we can unground and
connect to each antenna. Coax may go underground and emerge in strange
unexpected places so some buzzing out of connections may be needed. We
need to find where to connect to the massive ground planes buried under
the ground for these antennas. We need to see what the local noise
environment is at survey time. Hopefully we can get access to AC power
but should check out wall outlets to see they are powered.
6. We need to check and measure the noise bandwidth of our receivers so
we can get all signal to noise measurements corrected to the same
values. A small oscillator and noise source that is calibrated and can
be carried from receiver to receiver would be useful.
Thoughts and ideas?