Re: LF: Re: Ferrite wideband antennas?

[pws <pws@legal-medicine.de>]

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