TEFLON Insulator

[flintstone mop]

Hello Folks
Maybe someone can help me with an arcing problem on my HyGain 18HTJr.
I'm trying to get this antenna to be friendly to my station and it continually arcs out an insulator at the top of the mast. MFJ/HyGain keep sending the original black insulator and the antenna keeps failing..

A brief explanation: There are two masts involved. The bottom, consisting of 1 piece 2 inch X 78" heavy wall, which fits into a 2 inch X 81" which fits into another the same length. This last pipe has an insulator which fits inside and acts like a cup to support the rest of the mast. The top three sections are 1 1/4 X 82, then 7/8 X 82, then 7/16 X 82.
The 1 1/4 pipe fits INTO the insulator. At this point there are the cage loading wires for 80M.
The 1 1/4 inch pipe must fit inside the insulator as it is acting like a capacitor.
IF I totally insulate the 1 1/4 pipe from the 7/8 pipe using a cup shaped porcelain insulator the antenna completely changes and is no longer resonant on 80 or 40M ............
I need something to fit the same as the insulator Hy Gain uses only it does not break down. There must be extremely high voltages at that point to continually fail and arc. Only using 1000 watts....Antenna "rated" at 2kw. ha!

I could attach pictures of the insulator between weather systems and maybe my long explanation will make sense.
Here is a link to the PDF and illustrates the construction of the antenna.

http://www.qsl.net/4/4x6on/RADIO%20MANUALS/HY-%20GAIN/HY-GAIN--AV-18HTJR-5BD-VERT%20ANT.pdf

Whatever I am looking for must be able to support the top part, which is not heavy. The cage wires keep any stress or strain from happening to the insulator presently used.
The latest arcing point was at the very top at the collar of the insulator. Previous arcing started at the bottom of the cup part of the insulator.
The top mast and bottom must insert into each other to create the capacitor.
I tried to cut the bottom of the insulator off, thinking that moisture was causing the arcing. I support the top mast at the collar of the insulator with a hose clamp to maintain that insertion distance. To maintain whatever value they were needing. Then it arced at the collar which is much thicker rubber or whatever they are using. There are several others I am talking to and they have the same problem of arcing.
MFJ/HyGain has no idea why there is a problem or that there is a capacitor effect taking place between the two masts.

Any thoughts???
Any Teflon.......Real Dupont Teflon...available as tubing?? and thickness needed to copy the original?
Thanks

[N4LTA]

I'd make one out of teflon rod - US Plastics sells it by the foot - if you have or can get someone to make it on a lathe and.  I have not seen teflon tubing available. Teflon is not strong mechanically - but at the top of the antenna it would probably not need strength.

[W7TFO]

Hey Fred,

Why not measure the uuF when it is assembled, go back to your porcelain fix, and bridge it with a good HV cap of the same value?

No more zorch.

73DG

[ke7trp]

I got a probably stupid question...   Why not SLATHER on some Corona Dope?  Into the connection and over the entire insulator and even up the metal rod a bit. Then let it Dry and have at it?

[N5RLR]

From what I've read, some plastics are colored black with carbon powder in the mix when melted/molded.  The carbon molecules may be "exciting" in the presence of RF.  A neutral-color, RF-resistant material would be the way to go.  Delrin may be a choice.

[flintstone mop]

OK Thanks to you all........

DG: That has been rolling around in my head for a good while. I am going to experiment reading caps with the MFJ 269 and take the plunge to go out there. The WX is going to turn on me and snow etc etc........but as Don (KYV) says "prefect antenna weather"

Clark: Thanks for the idea. I'll give that consideration. Corona Dope was a reasonable fix for TV HV.
80M RF might be another challenge. BTW I googled corona dope and can't seem to get to the specifics of any properties for RF HV....This would be a great fix.

Mike: You are probably spot on. And MFJ does not realize the problem. It is black in color. They probably drifted from the original design. Everything was overkill in the late 50's and they probably did not have this problem when the antenna was first made.

Hugh: That might be worth looking into. The cage wires are doing most of the support and there would be no sway in the wind. And the top three rods might be just a few pounds.


Fred

[The Slab Bacon]

Phred,
         If you can find a piece of teflon or delrin stock, I can machine one for you. (have a lathe) I just dont have any teflon or delrin turning stock. Give me a call one evening on the telefonium to discuss it if needed.

[WD8BIL]

I cured a similar problem with a homebrew mount by wrapping the plastic with teflon plumber's tape. Worked great and still working on the 20M vertical after 12 years, Fred!

[WA1GFZ]

Teflon cold flows not good. Delrin is great under compression but not strong for pulling force. Fiberglass, fireproof outside grade is the strongest. I went through all this with our mechanical guy when I designed my LPDA up since '97.

[WD8BIL]

Teflon cold flows not good

Good for at least 12 years here, Frank.
But I'm just a buddly!

[flintstone mop]

Well
I'm gonna attach a pic of what's happenin and give it an emergency shot with a Buddly application of Plumber's Teflon..before the WX heads into deep winter.

The MFJ guy mentioned the same trick. I'll wrap all I got on that sucka.

And Frank, Thanks I might be contacting you. Thank you

Any chance that epoxy would have any insulating properties for RF?? Can't find any fast info google. I'm beating the clock between bus runs and make a Flintstone show.....

Fred

[W2VW]

The Buddly trick sounds like a good thing to try.

[N4LTA]

I think I have a chunk of delrin rod about 6" long and 1 1/2" diameter that you can have. Let me know.

Pat

[Jim, W5JO]

Out of curiosity Fred, where is this happening?  Is it near the frequency where you have the antenna tuned or 3% of center frequency or more away? 

I ask because I am considering one and want at wide bandwidth as possible.  I have been looking at it and the other Hytower.

[WD8BIL]

I was able to find 1" wide plumber's tape at Lowes, Phred. It makes the job a bit easier but the 1/2" stuphph works fine too.

Gud luk!

[flintstone mop]

Thanks for more input.
I attached pics of what is happening.
It looks like my time has run out. The WX got rainy on me.

A report to Buddly::::: Looks like two careful layers of the real Dupont Teflon Gas line tape is all I can lay down. 2 layers would withstand ?KV of RF???

Pat: I am PMing you with my address and will pay whatever for your Delrin

Jim:: I am trying to finish and use the 18HTJr...."The Poor man's HyTower"  A wire version of the REAL HYTower, and a few who are obviously not using legal limit OR have completely different ground conditions/installation,  love the antenna. I have only been within the 3% or so of the resonant point and arcing. I have not tried beyond the 3:1 SWR point.
As I ramped the RF power around 1200 watts CW the antenna crashed and the arcing started with the new insulator.
Maybe "back in the day" Hams did not use legal limit that much. 100watts might have been max for most hams during the late 50's

Fred.....thanks for the good info here.

[flintstone mop]

Another picture

Sorry
Try to show entire insulator assy.

Fred
EDIT: Thanks Buddly..I'll look for the wider stuff and check to make sure it is Dupont or at least PTFE..
what are the insulating properties of Teflon??? I'm only going to get two layers, if I'm lucky

[Steve - K4HX]

The antenna is trying to tell you something. 

[Jim, W5JO]

Now that I have read all you have done, I agree with Steve.  Something is not right here.  Matching maybe?

[flintstone mop]

WELP let's see if I can figure out what direction we're going here.
I read a flat SWR at the base of the vertical at 3720. 1.5:1.
I DID add a shunt inductor at the base to get the SWR from 2:1 to 1.5:1. There was a reading of 30 for X can never figure out if it is inductive or capacitive reactance.
The antenna is constructed as per the manual. Another owner had the same problem with this insulator. He replaced his and cut the bottom out and supports the upper mast with a pipe clamp. No problems since that time. He has just a ground rod, I have radials. He thought water was collecting in the cup part of the insulator and it caused the arcing. He only runs 1KW
Everything was good until I went past 1KW, 80M or 3720.
Legal limit on 40M and the other bands, no problem.
My first pass at this, I was ramping up the drive to the amp, and the first insulator arced out at 200 watts. We were in a wet period and water had collected inside at the bottom of the insulator. The arcing was at the bottom.
The new arc is taking place at the top at the collar, from the pictures.
So, the antenna is telling me that it cannot handle legal limit?? HyGain claims 2KW.
AEROSMITH Ham radio supply:
http://aero-smith.net/cart/index.php?main_page=product_info&products_id=108

claims 5KW.
So what are these new thoughts??
There is a lot of HIGH RF voltage on that top mast, cage loading. Should I add more cage wires?? That can also move the resonant freq selected by a jumper.
Thanks for the thoughts.
Keep 'em coming
Fred

[WQ9E]

Fred,

I have the regular 18HT version but depending upon how you set it up for 160 meter operation the same problem will occur.  The two official Hy Gain solutions for 160 are to feed it as an inverted L with a 40 meter trap where the horizontal portion attaches to the main tower section or base load it.  With base loading on 160 the power, according to the manual, must be limited to 150 watts to prevent arcing between the main tower and the top whip assembly.  It sounds like the smaller version has the same issue for 80 meters.

For high power on 80 you may have to also consider the inverted L type configuration but I am not sufficiently familiar with the junior version to know whether this is practical.

[Gito]

Hi

Maybe .the top section of the tube and the " C" between it and the bottom section of the tube make a series resonant circuit at the operating frequency so there;s a very high voltage developed across the top tube and the bottom tube at the  joint.

Maybe using a ceramic insulator,use a variable capacitor  between this two tube,drive it with a low transmitter power, then change the variable capacitor setting till the Antenna is resonant at the operating frequency,than change this variable C with a Fix high voltage C with the same value as the variable value (uuF)

Maybe ?

Gito

[Steve - K4HX]

I thought you had a dipole for 80 meters?

[flintstone mop]

Hi Steve
The reconfigured Dipole will also come up on 80M. Pretty powerful signals on that antenna.
It's main focus is for 160M....seems like 3705 can give nice results and nice QSOs

And Rodger....Roger your posting...maybe the same weakness for the Jr. I'll just work around the problem and try to strengthen the weak spot. And limit power, a little.

And Gito thank you. Yes there has been that thought rolling around in my head and a couple others here to fabricate a capacitor and insulate with stronger stuff, like porcelain...

There will be more play time after the bitter cold passes. RF always finds the weakest point to break down.
The Unihat vertical was the same way. The more power I put in, it put more electromagnetic waves out.
Thanks for the latest postings........
Fred

[WQ9E]

Hi Fred,

Here is the text as it appears in the 18HT manual:

WARNING
When using the LC-160Q Modification Kit
added to the 18-HT on 160 meters, do not
exceed 150 watts output power (300 W
P.E.P. out). Power levels in excess of this
limit will cause the antenna to arc.

The other Hy Gain 160 meter solution uses a trap/inverted L setup but it was also power limited to below the legal limit so I built a high power 40 meter trap feeding a vertical stub to get a little more vertical height for my inverted L setup.

I remember seeing an advertisement for the junior model in an older CQ but that is the only time I ran across one.  It looked like a pretty interesting design.