[Premium-Rx] Antenna Couplers

[jan at skirrow.org]

Hi Ben ...

I have two such devices. One is an old Collins built tube unit and the 
other is a TMC solid state unit. They both have essentially the same 
circuit. A matching network to the antenna, a cathode follower (or ss 
equivalent) on each channel to provide high input impedance and minimize 
signal loss, followed by a grounded grid amp (or ss equivalent) to isolate 
the output from the input and from each other, and finally a matching 
network to the receiver. The solid state version is extremely simple and 
could easily be built. They both have a high pass filter to keep out 
signals below about 2MHz and an upper frequency around 30-40MHz. There are 
VLF and UHF versions, which I haven't worked with.

I wrote an article on the Collins tube unit for Electric Radio, and ran a 
few simple tests comparing it to the much later TMC unit built for the 
military. The TMC gain was essentially unity - although there was a slight 
loss. Other designs I've seen build in a bit of gain. The Collins was down 
a few db. Both contributed a bit of noise. I haven't looked at their 
performance in the presence of very strong signals, but this could be a 
problem if the coupler gain was very high.

Both of the units I tested have a lot of miles on them, and I'd expect new 
units to perform better.

In practical terms I can see no difference in the on-air performance of my 
radios whether connected direct to the antenna, or via the TMC. There is a 
difference for the older Collins design, but the design of this unit is 
more complicated due to the use of a balanced transmission line to provide 
drive to the individual modules which is not flat with frequency.

Jan


At 08:55 AM 11/10/02 -0800, Ben Wallace wrote:
>I've been looking into antenna couplers.  I need to feed a number of 
>receivers from a single antenna.
>
>Are most couplers unity gain?  Any comments or recommendations from the group?
>
>Thanks -- Ben
>
>
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