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Re: [TowerTalk] Relay Box Measurements

Subject: Re: [TowerTalk] Relay Box Measurements
From: Jim Brown <>
Date: Sun, 26 Aug 2012 10:58:13 -0700
List-post: <">>
On 8/26/2012 6:54 AM, Jim Lux wrote:
> when you do the measurements (using some form of VNA, I presume), do you
> cal with a set of standards with UHF connectors, or something else?

I've done calibrations several ways. Fore these products, I'm only 
interested in performance up to 6M. I don't have a decent 50 ohm load 
with a UHF connector on it, and I'm most interested in VSWR. Also, 
whatever cable I connect to them will have a UHF connector on it, so 
including the male UHF in the measurement will be representative of 
actual performance.  So, to answer the question, I'm calibrating with an 
SMA load on N to SMA and a through N adapter to approximate the 
measurement plane, then replacing the through adapter with a pair of 
MIL-spec N to UHF males.

While I can certainly see the effect of the UHF connectors at 6M, the 
differences I'm seeing between one box and another, and between one port 
and another on the same box, are FAR greater than the effect of UHF 

One of the major design errors I'm seeing inside these boxes is a 
failure to provide a return path that parallels the switched path. That 
is, they depend on the chassis of the box as the return path, either by 
design, or by accident as the result of a board layout that breaks the 
ground plane of a two-sided board under the high side trace.  The result 
is more stray inductance added to the signal path (in addition to that 
caused by the relay contacts).  I've improved the 6M VSWR through the 
Top Ten A-B boxes by adding braid between the connectors and the board, 
and on the board over the breaks, and by adding a short open stub.

73, Jim K9YC

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