AntennaCraft ST-2: Is there a top or bottom?

[N9JIG]

So last night as I was trying to fall asleep (a dangerous time for me!) I was thinking about my ST-2 that I have deployed on a mast on the side of my house. I am less than enthused about the current performance, it works OK but not as well as I thought it would. As I was going thru the possibilities I wondered if perhaps it is mounted upside down.

The ST-2 (as well as the similar Channel Master 5094) is basically a set of vertical dipoles on a common mast, connected thru a balun to the coax leading to the radio. I know that it is symmetrical, it has identical elements above and below the boom. That it goes thru a balun tells me that it probably doesn't matter which side goes up, but does it really?

I am not that well versed on antenna theory to know this. Do vertically polarized balanced antennas connected thru a balun like this have a top and bottom?

I suppose I could go up on the ladder and reverse the balun connection to the antenna (easier than physically flipping it) but it is too hot, even by Phoenix standards to do so right now.

 

[mmckenna]

I don't think it matters since you are using a balun.
Thinking back to the folded dipole antennas I've installed, the only up/down orientation had to do with the moisture weep holes.

Easy thing to check with that fancy new ladder you have.

 

[dave3825]

I never did any tests but always took the wire that was the center conductor (checked with multimeter) and connected it to the element facing up. And the one from the shield to the one going down. To my warped thinking, to me its what made sense.

 

[mmckenna]

I never did any tests but always took the wire that was the center conductor (checked with multimeter) and connected it to the element facing up. And the one from the shield to the one going down. To my warped thinking, to me its what made sense.

That's not how impedance matching transformers usually work.

 

[vagrant]

@N9JIG - Experiement! It's only 80°F (27C) at 4:00 AM for some ladder climbing. Plus it's that dry heat

I never paid attention to how I connected the balun and I have put my ST2 antennas up/down at least a handful of times over the years. I never noticed a difference as long as I kept the antenna vertical, nor do I think there would be a difference. As I like to experiment, I have also used the ST2 horizontally and at a slight angle. The polarization difference definitely had an effect as one would expect.

Many of you know this, but for those that do not, the dB scale is logarithmic and not linear. Keep this in mind when also using handheld receivers/transceivers with the antenna attached, or placement on a vehicle.
- A 45° angle typically attenuates the signal around 3 dB = Half the signal is lost for both TX and RX
- A 90° angle typically attenuates the signal around 20 dB = This is 100 fold less signal power

Experiment! - Using a handheld with the antenna attached, rotate the radio/antenna to 90° on a weak signal...then keep going and have the antenna pointed downward and hear the signal increase again. Welcome to RF Magic! Show your friends. Impress your neighbors. Excite the children and pets.

* Note: Just when you think you have things figured out, Mr. Multipath is lurking around the corner. Experiment!

 

[dave3825]

That's not how impedance matching transformers usually work.

Somehow, I had a feeling.

 

[mmckenna]

Somehow, I had a feeling.

Well, to be fair, it would depend on what kind you have. The cheap TV antenna ones usually look like this and the primary and secondary are physically isolated:



There are other designs that do this differently, which might show you continuity:


Maybe you have a different one than the old style TV antenna types.

 

[YoShep69]

I have one mounted horizontally in my attic. Works great.
I have another one mounted in a spare bedroom 2nd floor, works great.
Might reverse the balun and see if it affects anything.

One of these antennas I bought from you SEVERAL years ago.

Greg
Cen IL