Hello Roelof,
Thanks for your tests.
Yes, i agree, these optical components are not the best coice for HF
applications. I even didn't expect much from them on 475 kHz but here
they still seem to work quite well. There are better components
available but these were on hand. And it is important that mounting of
the fiber optic cable is easy.
I would be completely satisfied if the system covers 137 and 475 kHz...
Due to the lower signal levels of the short active dipole i now
resonated the antenna to 630m, where i plan to do my tests. This
prevents IM and causes a significant gain!
Good luck!
73, Stefan/DK7FC
Am 12.07.2013 22:11, schrieb Roelof Bakker:
Hello Stefan,
Before using an optical link with an active antenna, I have been
testing it with a spectrum analyzer.
A FSH756V was used as optical transmitter and a FSH350V as optical
receiver.
Instead of a BF862, a J310 was used in the transmitter.
The FSH350V was followed by a standard mini-whip buffer amplifier.
The FSH756V and FSH350V are not suitable for HF use, I'm afraid.
These are rated for only 15 kBd.
The system was tested between 50 kHz and 10 MHz with a 1 meter and a
19 meter long optical cable.
I found that the cable loss varied from 0.48 dB/m at 50 kHz to 0.35
dB/m at 10 MHz.
As it works now, loss is rather severe; with a 1 m optical cable I found:
50 kHz: 5.4 dB
100 kHz: 6.7 dB
200 kHz: 11.0 dB
300 kHz: 14.3 dB
400 kHz: 16.7 dB
500 kHz: 18.7 dB
Using a 19 meter long optical cable another 8 dB should be added to
these figures.
None the less I will try to carry out a test with a mini-whip on 400 kHz.
To be continued.
73,
Roelof Bakker, pa0rdt
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