Hi all,
I'm continuing my monologue about my fiber optic antenna tests :-)
I just did some measurements to confirm the thought that i had while
beeing outside in the field.
It appeared strange to me: When grounding the vertical active dipole,
the noise rose by 2 dB but the WSPR signal levels rose by 15 dB.
Then it became clear: The resonance frequency of the resonated short
dipole MUST have dropped and so the levels change as well. So the
measurements cannot lead to clear results regarding the performance of
that antenna.
This is the resonance curve when the dipole is floating:
https://dl.dropboxusercontent.com/u/19882028/MF/630m%20res.png
Now, when grounding one of the dipole legs or touching one of them
(there is no difference) the resonance looks like that:
https://dl.dropboxusercontent.com/u/19882028/MF/630m%20res%2Bgnd.png
A difference of 7 kHz and 15 kHz :-/ and a higher input signal level!
Despite the loss of 7 dB, the levels are 15 dB higher. So it seems i
need much more gain if the plan is to run the dipole floating... And a
resonated dipole seems not the best idea for that kind of tests :-/
However, the signal voltage will be even lower if not resonated,
depending on the Q... And the IM problems....
I still don't want to use a OP AMP. Will do some changes on the design
now, using a non-resonated dipole, just some RC filtering. And the gate
should stay at 9V/2 for linearity reasons...
73, Stefan/DK7FC
Am 21.07.2013 17:56, schrieb Stefan Schäfer:
Back from the test...
It took place in JN49HK69GJ, a distance of 5.1 km to the TX.
But it wasn't a good idea to do it today. The sun was burning, i nearly
couldn't read the display of the netbook...
Better to go eating a LOT of ice now :-)
73, Stefan
Am 21.07.2013 16:00, schrieb Stefan Schäfer:
Hi all,
I just had a phone call to DK2DB who lives in 50 km distance. He will
send some WSPR signals soon. I will go out into the field again and do
my next test with the fiber optic antenna. My TX power is
reduced by more than 20 dB for that test.
If someone with a suitable signal, maybe PA3ABK, would support the
experiment with some test signals, that would be fine :-) I have to do
the test in daytime so that there is no skywave component, or QSB.
I will appear as DK7FC/p in the database and map then, in 30 minutes or
so. The location of the RX will be http://no.nonsense.ee/qthmap/?qth=JN49HK69DG
73, Stefan/DK7FC
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