Hi Peter,
try a BFP640,rBB 1ohm.Noise as low as 300pV/sqrt(Hz) is possible.Very
cheap,but one drawback,Ft is about 40GHz,not easy to get stable.For topband
I use BD139 (yes a lf driver),rbb 1,2 Ohm,very easy to use..
GL,73
Victor
PA3FNY
-----Oorspronkelijk bericht-----
Van: [email protected]
[mailto:[email protected]]Namens pws
Verzonden: donderdag 1 september 2011 15:58
Aan: [email protected]
Onderwerp: Re: LF: Re: Ferrite wideband antennas?
Hi Jim,
You wrote:
> ...
> I would be interested to know what method you used to determine SNR for
the
> different rod configurations.
> ...
Simply by going the broadband way and using a very low noise, very low
impedance pre-amplifier. It's easy to get voltage noises below 1nV/sqrt(Hz)
by running some transistors in parallel. Today I know that it's a low "Rbb"
of the transistor type what makes the difference. Unfortunately it's hard
to find this value in datasheets. I remember using BC327 or BC337 running
at ~10mA each. Fortunately current noise doesn't matter here.
The antennas had an inductance elsewhere around 0.5 mH. So the self
resonances lowered by 200-300pF added by the transistors had been at least
1 octave above the region of interest.
Obtaining spectra at a quiet spot will immediately showed the differences
of SNRs since some constant signals were available not influenced by the
ionosphere e.g. 147 kHz or Loran-C. I had/have such quiet spot here for
field-days, a constructor's trailer made of sheet included. This was of
importance for shielding the computer. Checking the depths of *both*
"nulls" will give some hints about the balance.
Peter, df3lp
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