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[TowerTalk] Loss in Connectors

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Subject: [TowerTalk] Loss in Connectors
From: (Tom Rauch)
Date: Mon, 21 Jan 2002 08:17:07 -0500
> Been thinking about the previous discussion about connector loss.
> The consensus was about 0.2dB loss per connector.

The consensus is absolutely wrong, and it is easy to prove they 
are wrong. Here's how you can use common sense to dispel rumor 
or folklore.  

1.) 0.2dB loss is about 5% power loss.

2.) The conductor AREA in the connector that is part of the actual 
connector and not the transmission line is less than one inch.

3.) Virtually all loss is concentrated around the center conductor of 
the connector in that small area.

4.) With 1500 watts, the connector would be dissipating **75 
watts** in about 1/2" to 1" of linear length deep inside the 

5.) Now imagine how hot the large surface area of a 75 watt light 
bulb is, or the tip of a 35 watt soldering pencil. Both have many 
many times more area exposed to cooling air, and both become 
VERY hot.

i'm not sure where that 0.2dB myth or rumor comes from, but it is 
obviously wrong by a factor of at least 40 times in a normal cheap 
connector!! Some connectors (like Radio Shack's connectors) do 
have exceptionally high loss, but I have measured them at 0.03 
dB!!! Some cheap adaptors have springs inside, and while loss is 
low they have a considerable impedance bump at VHF causing a 
very high SWR (and loss in the rest of the system).

Loss is the least of our worries with connectors, by far the real 
concerns are over-heating, voltage rating, and (if on VHF or higher) 
SWR. SWR is even almost meaningless at HF, because the 
connector is so short a horrid connector impedance can't cause a 
> Now was that putting two pieces of coax together which would consist
> of two PL259s and a barrel in between, or 0.6dB?  3 X 0.2=0.6dB.

That would be significant, because if it were correct the connectors 
would MELT. With 0.6dB loss, the connectors would dissipate 
13% of your power. With 1500 watts, you'd have 195 watts 
dissipated in about two inches or less of area. That heat would be 
enclosed inside plastic. It would not be a pretty sight or smell after 
the first few dots and dashes.

Since connectors don't require heatsinks, we can be positive 
numbers "0.2dB loss" are nonsense, even if many people repeat 
them as factual numbers.
73, Tom W8JI 

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