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[TowerTalk] Loss in Coax Switches ? Was Alpha Delpha.

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Subject: [TowerTalk] Loss in Coax Switches ? Was Alpha Delpha.
From: (Tom Rauch)
Date: Tue, 22 Jan 2002 08:47:59 -0500
> Like Jim, I was interested if anyone has ever done testing on the
> DowKey or the HOFI for a couple of common and seemingly well thought
> of switches.

As with the coax connectors, most of us can not measure the loss 
in a switch. If there is noticeable loss, and if you run more than a 
hundred watts or so, the switch will almost instantly become 

Only as you get into UHF, and if you run low power, might loss 
escape detection.

There is insignificant loss difference between a Dow Key and a 
open frame relay or conventional rotary switch at HF and lower. 
SWR starts to be an issue with some switches at perhaps 
100MHz, but SWR or an impedance bump in the switch does not 
necessarily mean noticeable loss increase.

The rule of thumb is in critical applications is a SWR of 3:1 has to 
be more than one electrical degree long to be noticeable. The SWR 
increase in a system with a one degree long bump of 3:1 SWR is 
small. The system SWR only changes from 1:1 with no bump to 
1.05:1 with the 3:1 bump that is one degree long!!!!

That means on 160-meters you can have 1.5 foot long bump of 150 
ohms or 16.7 ohms, and a perfect system's SWR would only 
increase to 1.05:1

Until the frequency approachs upper VHF, we can tolerate what 
many of us would think are some pretty funky impedances if the 
length of the bump is short.

That is why I don't worry a bit about UHF connectors or even hand-
splices at HF. The only real concern is weather and voltage and 
current ratings.

We are often far too concerned about impedance of connections at 

73, Tom W8JI 

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