[hpsdr] I had an idea.

[Jeff Cook]

Dear All,

I've had an idea, not a particularly good one, and certainly not 
original, but it's mine and I'm going to share it with you. I made the 
totally unnecessary purchase of a Trimble Thunderbolt which I have 
running continuously, I use it to synchronise Excalibur, now this turns 
out to be unnecessary as Excalibur is extremely accurate without help 
from elsewhere, however I now have a reliable and accurate 10 MHz signal 
source. What I did not have was a reliable signal level source, so I 
borrowed a friend’s Elecraft XG2 signal generator in order to set up my 
HPSDR unit, and then reluctantly had to return it. Now here's where the 
idea comes in, the 10 MHz output from the Thunderbolt is at +12.5 dbm 
+/- 2.5dbm which is to say the least a trifle on the large side for 
feeding directly in to Mercury, but fed to Mercury via a suitable 
attenuator would be just fine. Using the Pi Attenuator Calculator 
available at 
http://chemandy.com/calculators/pi_attenuator_calculator.htm I found 
that by using a series resistor value 390 K ohms and shunt resistors 
value 51 ohms, I came up with an attenuator valued at 83.77dB. Now then, 
with the attenuator inserted at the input to Mercury and with the output 
of the Thunderbolt connected to the other end of the attenuator my XG2 
aligned HPSDR unit gives the value of the signal as being -55 dbm, and 
it appears to be absolutely rock solid and not at all affected by 
movement of cables or the vicinity of my hands etc. So I now have a 
frequency standard and a signal level standard available to me from my 
Thunderbolt. The engineers amongst you will probably know all sorts of 
reasons why this is not an advisable way of doing things, but so far 
I've had no smoke and the amplitude of the signal does seem to be 
extremely stable.

I'm now waiting to be nominated for the Nobel Prize for cheap skating.

Jeff Cook, G0AFQ.