[Repeater-Builder] Re: Duplexer cable question

11 Jun 2004 10:37:35 -0000

I agree with Kevin.  We had to change out hundreds of LMR cables on a large commercial system because of noise and intermod being caused by the LMR connectors, and sometimes by the LMR cable moving on the tower.
 
A few other points:
 
9913 can distort the relationship of the inner conductor to the outer conductor when bent in a small radius.  This can happen over time and change the impedance of the cable.
 
LMR and 9913 have a very light braid covering on them.  This braid then attaches to the connector to make the electrical connection.  In my opinion, the foil does not make a good electrical connection to the connector, so you are depending on a limited amount of braid wires to make the connection.  Flexing the cable can break the braid inside the connector.
 
The amount of loss in a 2 foot jumper of good quality RG-214 is insignificant compared to LMR or 9913 cable.  The superior connection that you can make soldering RG-214 to a connector probably more than makes up for the losses. A 1 foot jumper of each type at 400Mhz would be:  9913= .034dB    RG-214= .041dB  LMR-400= .025dB  Using these figures, you would be saving about .016dB if you used LMR-400 insead of RG-214.  This would hardly be worth the effort.
 
If you really want to go all the way and "gold plate" your system, use hardline for the jumpers.  My favorite cable is Andrew 1/2 inch superflex.  It makes excellent mechanical connections, 100% shielding, it will bend to small radius, and is durable.  Unfortunately, UHF connectors are hard to come by for this type of cable.
 
Joe
============================================
Cables that are made of tin braid over aluminum foil can suffer from
dissimilar metal noise problems.  Those types of cables should be
avoided at a duplex site.
Only quality silver plated double shielded cables should be used in
duplex service.

Kevin Custer


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