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Re: Feed Line Loss @ Freq vs. Price



John,

That is a terrible spec for connector loss.  If you use N-type 
connectors you should not see anymore than 0.05 dB loss/connector up 
to 1296 (at least).  If you are getting more than that using 
N-connectors, then you are not assembling them correctly.  For cable 
under ten foot length, I cannot measure loss with any accuracy to 
make meaningful results.  If connectors had that much loss, it would 
show up with inches of coax.  I measure the loss using the duplex 
connections of a spectrum analyzer.  I can see 0.1 dB +/- 0.1 dB.

If you are using PL-259 (UHF) connectors for satellite 
use...shame!  They may not be terrible up to 144-MHz but above that 
they are a no-no.  Why?  Because they introduce impedance mismatch 
(bumps) => high loss.  And that is why they are no good.  Other good 
connectors are TNC and 7/16-din (real expensive).  BNC are OK but not 
for use where very good impedance match is important.  They are 
usable into mw bands though.  For low power the sma is preferred and 
good to 18-GHz (some are good even higher).  N-connectors have been 
used at 10-GHz but not as good as sma.

Side comment to Nate:  What is your problem with LMR cables?  They 
are essentially double-shielded and lower loss than most coax other 
than hardline.  Times Microwave LMR line of coax has equivalents up 
to 1-5/8 inch hardline for loss specs.  If you mean use as jumper 
cables between the duplexer and the Tx and Rx of a repeater, then one 
should use RG-143 or Belden-8214 double-shielded cable.  That is a 
shielding issue not a noise issue.  If shielding is inadequate, 
repeater de-sensing can occur that effects the receiver sensitivity 
(Tx RF gets into the Rx).

I have a commercial 75w VHF repeater using about 60-feet of LMR-600 
in service for over ten years with absolutely no problems.  This site 
has about 7 other repeater users, BTW.

73 Ed - KL7UW

At 01:17 PM 5/10/2007, John Champa wrote:
>In calculating cable run losses (that I have constructed) I use the
>figure of 0.5 dB loss per connector.  Perhaps somebody makes them
>better than I do, however.  (HI)
>
>73,
>John - K8OCL
>
>
>----Original Message Follows----
>From: "Nate Duehr" <nate@natetech.com>
>To: amsat-bb@amsat.org
>Subject: [amsat-bb] Re: Feed Line Loss @ Freq vs. Price
>Date: Thu, 10 May 2007 13:46:35 -0600 (MDT)
>
>
>  > This is true.  However, the connectors you must put in line from past the
>  > rotator
>  > to regular LMR-600 to the station would likely eat up all the delta in
>  > loss!
>
>To continue the thread accurately - we now need to know how lossy specific
>connectors are.
>
>All of these "runs" described so far are about 40', a "typical" number for
>a small tower or structure many hams might have... but if you're running
>100' up a tower or structure... the clear winner starts to emerge...
>
>1/2" (or bigger!) hardline with a short jumper of something flexible at
>the top and high-quality N-connectors at that junction.
>
>Right?  Feel free to do the math... if you can find real world numbers for
>connector losses that you trust.
>
>Also keep in mind if you ever plan on "re-purposing" any of the cable runs
>up the tower for duplexed service (going to put a repeater on the tower
>via one of your runs of cable), LMR is a very VERY poor choice for
>duplexing... its design leads to noise and desense problems.  Not a
>problem in non-duplexed service, though.
>
>--
>Nate Duehr, WY0X
>
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>
>_______________________________________________
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73,
Ed - KL7UW
======================================
  BP40IQ   50-MHz - 10-GHz   www.kl7uw.com
144-EME: FT-847, mgf-1801, 4x-xpol-20, 185w
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