Victor
I am having the opposite experience with my antennas. I have to insert
Attenuation to avoid overload to my Receivers.
Now QRV tonite on 136.5 cw es 137.7 qrs3
de mal/g3kev
----- Original Message -----
From: <[email protected]>
To: <[email protected]>
Sent: Thursday, September 01, 2011 5:21 PM
Subject: RE: LF: Re: Ferrite wideband antennas?
> 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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