Mast Material / Metal ?

[jrd426]

Hi guys. For a fiberglass type base antenna big stick, antron etc, is a metal mast pipe needed vs say a finerglass pole. Is the typical metal mast needed for this type antenna for counterpoise ? Lets use a antron type antenna without groundplane / kit. Would the coax coming straight down attached to a fiberglass pole work ok compared to a metal pipe. Any difference with swr or anyrhing ? Thx!

 

[loosecannon]

they would actually perform better on a fiberglass mast.

metal masts create a "leaky capacitor" to ground and can mess with radiation patterns.

strength could be an issue.

with the antron 99 in particular, you would want to make sure the first 9 feet of coax coming down from the feedpoint runs straight down vertically as this antenna uses the first 9 feet or so of the coax for a counterpoise.
that would also mean that if you wanted to use a choke balun, you'd want to put that 9 feet down from the feedpoint as well.

not sure about the big stick but i believe you could choke at the feedpoint of that one.

now here's something SUPER important to know. to achieve this improved performance you can't run a long ground wire down from the feedpoint as this would essentially be recreating the metal mast.
this means that you MUST have a lightning arrestor (a real one) connected to a ground rod (or more than one) before the coax enters the shack.


this subject has been covered a lot here on the forum, and many of the discussions centered around the avanti astroplane design so search those terms to find good threads.
there is also a thread about isolating end fed antennas from their support structures that is a good read.

hope this helps!
LC

 

[jrd426]

they would actually perform better on a fiberglass mast.

metal masts create a "leaky capacitor" to ground and can mess with radiation patterns.

strength could be an issue.

with the antron 99 in particular, you would want to make sure the first 9 feet of coax coming down from the feedpoint runs straight down vertically as this antenna uses the first 9 feet or so of the coax for a counterpoise.
that would also mean that if you wanted to use a choke balun, you'd want to put that 9 feet down from the feedpoint as well.

not sure about the big stick but i believe you could choke at the feedpoint of that one.

now here's something SUPER important to know. to achieve this improved performance you can't run a long ground wire down from the feedpoint as this would essentially be recreating the metal mast.
this means that you MUST have a lightning arrestor (a real one) connected to a ground rod (or more than one) before the coax enters the shack.


this subject has been covered a lot here on the forum, and many of the discussions centered around the avanti astroplane design so search those terms to find good threads.
there is also a thread about isolating end fed antennas from their support structures that is a good read.

hope this helps!
LC

Thanks LC. Helps allot. 73

 

[sp5it]

It is enough to insulate antenna from mast.
Mike

 

[Alexis Mercado]

Do I need to isolate an A99 if I install it on top of a 3 element Mosley TA-33 Yagi antenna ? A99 will be around 4-5 feet above the yagi .

 

[Alexis Mercado]

Do I need to isolate an A99 if I install it on top of a 3 element Mosley TA-33 Yagi antenna ? A99 will be around 4-5 feet above the yagi .

?

 

[Dusty1USA]

Hi guys. For a fiberglass type base antenna big stick, antron etc, is a metal mast pipe needed vs say a finerglass pole. Is the typical metal mast needed for this type antenna for counterpoise ? Lets use a antron type antenna without groundplane / kit. Would the coax coming straight down attached to a fiberglass pole work ok compared to a metal pipe. Any difference with swr or anyrhing ? Thx!

Antennas like the A-99 or Tram 1498 don't need a counterpoise. They are 1/2 wave over 1/4 wave antennas. They have their own counterpoise.
The also don't need a GP.
I have my Tram mounted on top of a 3/4" steel pipe. I have no issues with at all.
SWR 1.1 to 1.2 from ch. 1 to ch. 40.
RF power meter doesn't even move the needle.

 

[BC Coyote]

Antennas like the A-99 or Tram 1498 don't need a counterpoise. They are 1/2 wave over 1/4 wave antennas. They have their own counterpoise.

While this is true in theory, in actual practice it is very rare to find an A-99 or similar antenna that ISN'T affected by its counterpoise. They are also VERY susceptible to having CMC's running back down the coax to the radio.

It's very easy to tell if your coax is acting as a counterpoise. Measure your SWR, and then add a couple feet to the coax (using a barrel connector and jumper) and see if the SWR changes at all. If it changed when you added coax (or moved it significantly) then the coax is acting as a counterpoise. If the antenna is perfectly matched there will be NO change in SWR no matter what length the coax is or how it's routed/coiled.

The A-99 groundplane kit, while it does nothing to help rx or tx, DOES help a whole bunch with eliminating CMC's and helps match the antenna to it's coax correctly.

 

[sp5it]

They have their own counterpoise.

Where it's located?

 

[linearone]

everyone is afraid of antennas with radials. I dunno why.

 

[Crawdad]

attached to a fiberglass pole work ok compared to a metal pipe

Might think about painting that fiberglass mast. UV wreaks havoc on fiberglass over time. Or use something metal.

7 3

 

[Eldorado828]

I'm in the process off getting mine up in the air within the next few days being life permits.

I'll be concreting a section of 10' 2" galvanized water pipe, on top of it will be a 14' section of 1-1/2 galvanized with the top section being a 10' 1-1/4 galvanized that will slide into the middle section. Somewhere up high it will be mounted to the house for extra stability. That should get me going for a little while.

I just don't trust any other way other than steel in my part of the world and it has worked great with any antenna I've ever used.

 

[AK #5]

I use a 30' fiberglass push up pole, purchased from DX Engineering, and with a Sirio Tornado 27 sitting on top. Grounded the antenna with 5 AWG wire, and no CMC getting in like it was with the Tram 1498.
Very pleased with this setup.

 

[Dusty1USA]

Where it's located?

There is a coil in the base.