PDL II questions

[loosecannon]

Hi all.

I have a local friend who just put one of these up, and it's his first beam antenna.
He's having some issues getting the performance out of it that he believes he should.

I noticed that his signal was almost 1 full S unit lower when the beam was pointed at me as opposed to his groundplane antenna which is at a similar height. (roughly 36 feet above ground)

Having never owned one of these antennas i really don't have any good advice to give him in order to help, but i would like to help if i could.

he's got the SWR low on both horizontal and vertical, apparently about a 1.2:1 or so.

He did not put any common mode chokes on the feedlines, and i believe they are running down the tower right next to eachother if that means anything.

I think he should look into some snap on ferrite from palomar engineers, but don't want to waste his money.
looking for opinions on that.

so, to those who have experience with one of these antennas, or to anyone who has modeled it, where should he be looking for performance increases?

The beam seems to be quite narrow if that helps.

Thanks for any tips or advice on what it takes to make one of these antennas perform.
LC

 

[groundwire]

Common mode current on the feedliine will distort the radiation pattern, not decrease the signal strength, although anything is possible. Is the feedpoint hooked up correctly?(Ie: connections reversed). Cross polarization during your test?

 

[midnight special]

if useing the original avanti switch box open and make sure that the wires inside are not touching,, i had that happen to me once on a set of moonrakers and a fellow in kentucky had the same problem on his pdl2

 

[undertaker]

I had one till a storm took it down. Great beam but hard to tune

 

[Handy Andy]

One neighbor from ages ago put more wire on the "trapezoid" to get a better "Back door".

Remember too, that it has Horizontal and Vertical polarization.

So when you see 1 S-unit less, was it beamed at you vertical or horizontal?

The "gammas" are like the others say, and contrary to the Manual - difficult to tune...

It's supposed to be easy but remember this is a COMPACT antenna that sends part of it's RF radiator AWAY from the reflector - much like that of a simple 1/4 wave whip over a counterpoise the typical Ground Plane image which that rear "net" appears as counterpoise, then the gammas take over the phasing - thru their harnesses of coax - to generate the polarizing effects thru those driven "crosshair whiskers"

While you're looking at it...
This orientation - Rear to Rear
Front Hub - facing you and it is on your left in this orientation...
Your Right side of the antenna is VERTICAL Gamma
On Your LEFT is the antennas HORIZONTAL Gamma

It's like looking at a broken antenna half-way up they "split it"
- only you have two radiators, like a beam antenna would have - one vertical the other horizontal.


The Gammas are LOWER with points towards Front Hub
Their opposite sections short back to CENTER mount​

 

[Robalo]

Also this might help

 

[Marconi]

LC, I'll model this idea tomorrow.

 

[Marconi]

I have a local friend who just put one of these up, and it's his first beam antenna.
He's having some issues getting the performance out of it that he believes he should.

I noticed that his signal was almost 1 full S unit lower when the beam was pointed at me as opposed to his groundplane antenna which is at a similar height. (roughly 36 feet above ground)

Having never owned one of these antennas i really don't have any good advice to give him in order to help, but i would like to help if i could.

LC, I planed to make a 2 element Quad model or look for one I've already made...that demonstrates the problem I think your buddy is experiencing. I see some bad Common Mode Currents flowing big time on what I presume is a vertical polarity Quad that you are talking about.

Such CMC problems can and will skew the pattern badly, and usually hurts the performance big time.

I found this picture by Homer that tells the same story and shows how to help solve the problem.

Check out the coaxial choke that Homer has at the bottom feed point on his Vertical polarity Quad in his picture.

I'll also do the model, because it shows me, it demonstrates the problem in the antenna pattern and the image views of the antenna.

I remember we were discussing a similar issue with you installation of an Old Top One antenna on a non-conductive mast.

So, if you don't see in your "mind's eye" what I described here...just ask me and I will try and explain.

 

[Marconi]

Here is my model of a Vertical 2 element Quad with and without CMC issues.

 

[loosecannon]

You rock Marconi.

thanks for doing that.

yes, he was switched to vertical polarization when doing the testing.

i'll look over the model and post back if i have questions.
LC

 

[Marconi]

LC just as a note:

I think Homer's image shows his quad is horizontal...unless he is voltage feeding it somehow. I think he adds a coaxial chokes or another type of choke to all his antennas...just to be sure.

Bob and Homer among a few others have been telling us all about this Common Mode Currents problem for some time now.

My model for the Horizontal Quad does not show a need for a choke, and I think it is because there is 20+ db difference between vertical and horizontal signals, and that may suggest why my model shows no need for a choke,

BTW, I found to do a really good job of making the feed line look invisible was to use 2 chokes instead of just 1. The only way to really be able to really tell however, would be for me to add a feed line to the model...and I did not go to all that trouble.

Also note in the models that the Quad without the chokes, skews the pattern badly in the back and noticeably raised the maximum gain pattern to 28* degrees above the horizon vs. the lower maximum gain angle of 10* degrees for the model with a good working choke. It is sometime what we don't see that produces a signal that is disappointing...and then a sharp guy like you and your buddy are able to know the difference...because you tested you results.

I applaud you both for being curious, and not just getting all "giddy" on installing a new antenna.

 

[Marconi]

You rock Marconi.

thanks for doing that.

yes, he was switched to vertical polarization when doing the testing.

i'll look over the model and post back if i have questions.
LC

I had 3 radio buddies back in the days that had PDL2 antennas, and 2 of the guys were always able to hear crickets at far distances in either polarity.

 

[Handy Andy]

You rock Marconi.

thanks for doing that.

yes, he was switched to vertical polarization when doing the testing.

i'll look over the model and post back if i have questions.
LC

Well, there are at least two PDLs'

One designated as PDL2

Another is PDL -II

Which one are we working on?

​

 

[Marconi]

Andy, this one is a Maco Y- Quad........................................This is the PDL2

I had one and it worked just like Loosecannon describes for the vertical side, and maybe even for the horizontal too. I mostly remember being disappointed.

Back then I had not idea what the problem could have been or how to fix it. So I used the parts to help build my homebrew 4 element yagi on a Moonraker boom, and that worked great for over 10years until a hurricane was coming and I took it down and stored it away.

 

[Handy Andy]

@Marconi - Then for my own curiosity - the PLD-2 - using a boom "gamma" (those front elements like you have in the pictured)...does that design offer similar response compared to the (Gamma again - but circular) as the "II" type of curved arms to offer some form of compaction (compact design?) - how do these two designs differ?

I mean if you have to write a book, well, I'd certainly would read it.

But to help the rest of the user base still here, help them to understand the subtle - profound - differences between the two different constructions.