Hi Stefan and all,
I am looking very forward to your test results of your Mini-Dipole + fiber
optics.
FYI,
Last year, I made a Mini-Dipole with an instrumentation amplifier AD8429 set
at Av=10 (+20dB),
which worked fine, and is in current use.
The dipole elements are aluminum L shape angles, 50cm long each.
I noticed that adding common-mode chokes, LPF on the coax, isolation
transformer to the RX
gave no improvement of signal to noise ratio,
but on the Mini-Whip they slightly did.
I interpret this that the mini-DP is more immune to coax induced noise.
At the end, they are both good, when common-mode-choke, LPF, iso-trans. are
added to the Mini-Whip.
They are both battery operated, a motor-bike battery, 6.5Ah, but it looks
like I don't need.
Gain setting of Av=10 (+20dB open load) seems to be too high, or the DP too
long.
The external noise sounds more smooth on the Mini-Whip, and the Mini-DP
slightly "hard",
judging by my ears, and I think the amplifier is slightly overloaded.
I did not perform any quantitative evaluation,
except that the amplifier alone had a bandwidth of 10kHz to 1MHz
at about 1dB down, on the bench.
73's
Hideho YAMAMURA, JF1DMQ
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Stefan Schafer
Sent: Saturday, July 13, 2013 9:28 PM
To: [email protected]
Subject: Re: LF: Re: MiniWhip antenna, fiber optic TEST SIGNALS NEEDED on
630m WSPR
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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