Anyone know why a balun would work like this?

Status
Not open for further replies.

Darla_42

Member
Premium Subscriber
Joined
Feb 3, 2010
Messages
5
I was in the process of expermenting with using random length wire antenna(s) for my BR330 scanner, when I accidently notice something, and decided to try and go somewhere with the "discovery".

Basically what I ended up with is as follows.

A simple old Radioshack 300 75 ohm matching transformer hooked to a female coaxal - to - bnc adaptor, which then was attached to a male bnc - to - sma adaptor, as this scanner has a sma for the antenna terminal. I then connected a 18 inch telescopic antenna to only one of the connections on the 300 ohm side (one of the 2 connectios on the 300 ohm side seems to work better than the other). The other terminal was left unused - as if it was not there.

To my surprise through nearly all spots on the bands I checked, this setup performed more like a much much larger antenna, better than an old 6 foot telescopic whip I once purched on ebay - i think form someone in the UK.. The areas of the spectrum it seemed to not have much of an impact on was on the LW/MW bands and between 420 - 450 MHz.

On the 800 - 900 MHz bands it worked best when I shorrtened the antenna to around 6 - 8 inches.

At first I was almost certain that I was causing major regenerations between the balun and my scanner, because the balun I used iwas housed in plastic.So I tried placing 25 feet of double shielded coax between the scanner and antenna/balun and it still worked quite well. So I pretty much rule out regeneration.

I went out of my way to hook up a second identical antenna to the unused terminal on the balun
and when iI did - I lost all of the "gain" that I was getting.

So whatever may be happening here.....
And not to look a gift horse in the mouth - should that be the case
I have been going crazy trying to figure out how this "gain" is coming about.
As I said this was an accident, and if it's one that is worthy, i'd like to know if anyone can tell me
what I have done - i'd lke to understand how it does what it does, not just what it seems to do.....
And equally important.... could it cause damage to my scanner....Untill I really know atleast this --- My little "discovery" will stay put in my desk.
Thanks for any information anone of you may have.
 

k9rzz

Member
Joined
Dec 12, 2005
Messages
3,164
Location
Milwaukee, WI
I think you're just matching the antenna impedance well and getting good results.

When you hook up the second antenna, the sigs may be canceling each other out. Try to separate them as much as you can.
 

Darla_42

Member
Premium Subscriber
Joined
Feb 3, 2010
Messages
5
That makes sense, but...

I can appreciate and understand the process of cancelling signals, and that possibly I got lucky in matching impeadance.

As far as trying to use 2 antennas on this balun would be problematic since I want to keep this small as I primarily us my scanner on the go.

What does not make any sense is the results I am getting from the use of a single antenna, leaving the other terminal unconnected. It doesnt make sense with what I know about transformers, and I am really left shaking my head because I cannot find any references on the internet regarding using a balun in this fashon. Basically one terminal is getting a given impedance from the antenna (I'd assume rather high z give the length), and the other terminal is getting infinate impedance, whatever impedance the screw terminal has (if any).


The drastic mismatch on the 300-ohm side ----
--- if its being transformed to a decent 50 - 75 ohm secondary,
--- Then I just simply lucked out this time
 
Status
Not open for further replies.
Top