[MilCom] Question on multi scanner hook ups

[lrk]

On Sat, Aug 27, 2005 at 05:23:07PM -0400, Ron wrote:
>
> Do directional couplers with -xx dB isolation taps help or hinder multi 
> scanner hook ups to a single antenna, in regards to them introducing 
> birdies or interference back up the antenna cable to the other scanners 

Yes, they help. It is still hard to keep the scanners from affecting each 
other but this is the right way.


>     I was given several of these with F connectors (input, output and 4 
> isolation taps on each one,) with the 4 taps on each one being the same 
> 'isolation' value of either -15, -20, -25 or -30dB, by a friend who does 
> CATV installs. Units are marked 4 Way directional tap, 5-500 MHz.
>    Price was right (free), but before I start  buying a bunch of F 
> connectors and adapters to hook the scanners up to my present single ICOM 
> R7000 Disconne and experiment, I figured I'd throw it out to this august 
> group.

I have all my 800 MHz receivers done this way. I found the CATV cable (RG-6)
was much better isolation than any RG-58 I have and the price was right too.
Thus you might do real well for the cost. Would be better if you had more
expensive stuff. I use the Radio Shack one-piece crimp connectors and then
adapters as necessary.

BTW, there are some such devices with numbers like "90db" on them but this
is isolation from the outside world. Hopefully your "isolation" numbers are
between ports rather than from the outside.


>    And while you are all online here, would they be of any assistance 
> isolating an RS-392 Short wave receiver from a Racal 6790 using a single 
> shared HF feed line? Would they work on frequencies below 5 MHz? With 
> degraded functionality?

Yes and yes. And if this helps get the HF antenna away from the computers,
even better.


>    Should the unused taps/outputs be terminated with 75 ohm terminators?

Yep. I found some at Home Depot. Not real important but the right thing
usually works better.


>    If you think I have any idea of what I am talking about, you are 
> mistaken!

I often point out that I know many ways to blow up a transistor because
I've tried them all. Antennas are a black art anyway so try things and
learn.


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