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Re: LF: Re: POOR ANTENNAS

from [M0FMT] [Permanent Link][Original]
To: "[email protected]" <[email protected]>
Subject: Re: LF: Re: POOR ANTENNAS
From: M0FMT <[email protected]>
Date: Mon, 18 Feb 2013 18:53:22 +0000 (GMT)
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Roger and group
 
Mal is right next stop the Shetlands, however....
 
I have come to the conclusion that yes a large capture antenna (Marconi etc) will out perform frame ants and active antennas for reception on MF.
However a large capture antenna in a noisy location will pick up huge amounts of local noise as well which most likely will swamp the DX signal. So large is not necessarily beautiful when it comes to receiving in urban and not so urban areas, like in the country side where mains is distribution via arcing 11kV on over head lines like my site.
 
Even in a small community like mine of three houses spaced out, with neighbours who are non techie types without PC or massive TVs you still can have a very high radio noise on receive. In fact local urban amateurs appear to have less noise than me and have much better MF reception (possibly owing to underground electrical services). I have actually gone out in my car (a well reported event) with my one metre square frame ant and set up near stations with good MF reception to prove that an Urban location need not be a barrier to fair if not down right excellent MF reception.
 
Since most noise comes from your house or the immediate neighbours house the thing to do is mount an active antenna as high as possible in the quietest place on your 40ft square garden. Take the signal down via a well screened coax that is well earthed and fully screened right up to the RX input. The signal will be weak but the signal to noise ratio will be good and stand post mixer amplification without too much wanted signal to noise loss.
 
I have tried a non active whip (2m 7/8th wave) up at 45/50ft the 50 ohm coax straight into the 50ohm rx input (huge mismatch) but the coax screen is continuous right up the the RX input. Again the received signals are weak but the signal to noise is very good. It is about minus one dB down on the inverted L (up 40ft x 128ft lg) when the inverted L is actually usable for RX i.e. no noise about which does happen.
 
In recent WRSP (wait while I wash my mouth out) RX tests the SNR was comparable with stations who purport to have a superior Rx facility on MF.
 
There is more I could add concerning terrain, take off and sea paths but not yet fully formulated my views on this.
 
I don't know if this has added anything useful but noise picked up from local sources is the issue on MF IMHO. Gain via noisy amps doesn't help.

73 es GL Pete M0FMT IO91UX
From: Roger Lapthorn <[email protected]>
To: "[email protected]" <[email protected]>
Sent: Monday, 18 February 2013, 17:25
Subject: Re: LF: Re: POOR ANTENNAS

Quite so Graham.

Many are plagued by unbelievable noise levels these days. It would be too much to expect Mal to try to empathise and suggest helpful ways of mitigating this.

I just wonder how Mal would fare living in an urban semi with a 40 foot garden like mine?

73s
Roger G3XBM


On 18 February 2013 17:01, Graham <[email protected]> wrote:
May be , may be not  Mal
 
The system is  reading  the  s/n   at the  Rx   and  not the   field  strength ........  depends on the  local  noise level ,   rst   159  or  599  , carrier  still  S9  ,   1= qrm     5= no  qrm
Sent: Monday, February 18, 2013 4:49 PM
Subject: LF: Re: POOR ANTENNAS

Example
I am receiving PA3EGO + 2dB another UK stn is showing -22 at a shorter distance. A difference of 24 dB
and this station says he is an Expert!!
 
 
----- Original Message -----
From: mal hamilton
To: rsgb
Sent: Monday, February 18, 2013 4:42 PM
Subject: LF: POOR ANTENNAS

MF
One thing the wspr DB shows is how poor some Receivers/Antennas are comparing like with like approximately same distances from Transmitter.
 
g3kev
 



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