Topband: Palomar R-X Noise Bridge

[Carl]

----- Original Message ----- 
From: <donovanf at starpower.net>
To: <topband at contesting.com>
Sent: Friday, February 14, 2014 11:42 AM
Subject: Re: Topband: Palomar R-X Noise Bridge


> Null depth is a function of cable loss.

** Yup

>
> Heliax produces the deepest null, small diameter coax (RG-59, RG-58) is 
> quite poor


** The highest VF and lowest loss produces the deepest null but also the 
least deep null bandwidth due to the higher Q. I used CATV RG-11 for my 
stubs and could get a good 25 dB+ null compared to about 12dB for RG-58. I 
had to add pieces for CW contests on some bands.
The 25dB was sufficient to operate on any other band and put the TX phase 
noise in the noise.

Carl
KM1H


>
> 75 vs. 50 ohm should make no difference.
>
> 73
> Frank
> W3LPL
>
> ----- Original Message -----
>
> From: "Charlie Cunningham" <charlie-cunningham at nc.rr.com>
> To: mapa50 at windstream.net, topband at contesting.com
> Sent: Friday, February 14, 2014 4:16:30 PM
> Subject: Re: Topband: Palomar R-X Noise Bridge
>
> I would expect it to work OK with 75 ohm cable. An open-circuited 1/4 wave
> line looks like a short at its sending end and you would be looking for a
> null as the line reaches a 1/4 wavelength, so I would expect the method to
> work fine with 75 ohm line. In fact, the 50 or 75 ohm line, if we consider
> it to be lossless would be operating at infinite VSWR so I wouldn't think
> the modest difference in characteristic impedance would make any real
> difference.
>
> 73,
> Charlie, K4OTV
>
> -----Original Message----- 
> From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of
> mapa50 at windstream.net
> Sent: Friday, February 14, 2014 12:18 AM
> To: topband at contesting.com
> Subject: Topband: Palomar R-X Noise Bridge
>
> I have a question about using the noise bridge. I have used it cut stubs 
> to
> 1/4 wavelength using 52 ohm cable with no problems. I now need some stubs
> using 75 ohm cable which I have on hand.
>
> Will the same procedure work for 75 ohm that works for 52 ohm cable, or
> will the different impedance need to be accounted for. I started to cut
> cable and this question came to me. My first thought is that it will work
> fine, but I am not sure. I did some searches on the web but found nothing
> about it. Any help would be appreciated.
>
> Thanks, Pat Armstrong
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