From: "Mike Dennison" <mike.dennison@ntlworld.com>
To: rsgb_lf_group@blacksheep.org
Date: Sat, 17 Mar 2018 14:19:29 -0000
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Subject: Re: LF: Pre amp *after* BPF??
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I would go along with Rik in principle, but beware of high static 
levels giving a misleading high figure of "antenna noise". This test 
only works on low static days. I would, in any case, suggest a 
"threshold" of several dB to ensure you are really looking at the 
band noise rather than static peaks. Perhaps ensure the "antenna 
noise" is at least 3dB more than the receiver noise. I have seen 
posts in the past suggesting that this figure should be as much as 
10dB.

Mike, G3XDV
===========


> Keep in mind that you only need a pre amp if the "antenna noise" is
> below the receiver noise.
> 
> Most receivers have reduced sensitivity at LF / MF, but the
> noiselevels at these frequencies is high compared to HF.
> 
> Easy to check: Listen (with connected antenna) on a quiet frequency
> (only noise, no signal). Next disconnect the antenna. If the noise
> level decreases you do not need a pre amp (in fact a pre amp will only
> deteriorate the IMD behavior and thus create more ghost signals).
> 
> 
> 73, Rik  ON7YD - OR7T
> 
> 
> ________________________________
> Van: owner-rsgb_lf_group@blacksheep.org
> <owner-rsgb_lf_group@blacksheep.org> namens Andy Talbot
> <andy.g4jnt@gmail.com> Verzonden: vrijdag 16 maart 2018 12:54 Aan:
> LineOne CC: Chris Wilson Onderwerp: Re: LF: Pre amp *after* BPF??
> 
> After, definitely
> 
> Before is applicable to VHF and up where equipment noise figure
> dominates sensitivity and a filter in the antenna side wold add loss
> and degrade overall NF
> 
> At HF and certainly LF, atmos noise dominates to noise figure is
> unimportant.   That way you get the benefit of rejecting strong OOB
> signals that may stress even the preamplifier
> 
> 'jnt
> 
> 
> On 16 March 2018 at 11:36, Chris Wilson
> <dead.fets@gmail.com<mailto:dead.fets@gmail.com>> wrote:
> 
> 
> Hello  LF'ers,
> 
> Been  Googling and see a mixed response to should a receive pre-amp go
> before  or after a BPF. I have mine before the pre-amp, does the panel
> concur with this being correct? Thanks!
> 
> Aerial,  isolation  transformer  for  ground  loops, BPF, pre-amp, Red
> Pitaya as the LF receiver.
> 
> --
> Best regards,
>  Chris                         
>  mailto:dead.fets@gmail.com<mailto:dead.fets@gmail.com>
> 
> 
> 
>