TEFLON Insulator

[Jim, W5JO]

I think Rodger is onto the problem Fred.  You are seeing the effects of high voltage at those points and unless you do something like Gitgo has proposed, you will have this trouble.

The simple solution is as Rodger suggests, make 160 and inverted L if possible.

[flintstone mop]

Very good info. It looks like whatever I do will just reduce the problem cuz High Voltage RF will find the next weak spot sooner or later........

I'm heart broken    No problem on that. I can go full scrote on the dipole. And I can break out the DX 100 for the Jr.
I'll have to activate and monitor the ALC on the amp for that band on the Jr. not to exceed maybe 500 Watts...
I think the Delrin or Teflon tape or both will get me to some higher power.

Thanks again Q9E......for taking the trouble to quote the manual. A lot more info here than from HyGain.
Fred

[IN3IEX]

Remove everything, antenna included.


If this works, make wire dipoles, one for each band and connect all to the same cable.
Wires can follow you preferred path.
No inductors, no capacitors, no tuners, no spark, no problem.

    It worked for me.

[flintstone mop]

Remove everything, antenna included.


If this works, make wire dipoles, one for each band and connect all to the same cable.
Wires can follow you preferred path.
No inductors, no capacitors, no tuners, no spark, no problem.

    It worked for me.

I will never do that. Coax and a tuned dipole........I prefer my OWL and the dipole I have now using a nice big HB tuner for open ladder line. I don't worry about losses or high SWR on OWL.
The vertical will get figured out soon for long distance work.

And Jim: The antenna is 80-10M, I'm not interested in 160M, my dipole is perfect for 160M.......maybe not DX, but that will be another time.
Maybe next year, I can use the utility pole and run another wire (Vert part of the "L") up at L 65 feet high and connect to the horiz. (part of the existing dipole) wire through a little vacuum switch at the top. Getting radials out is no problem when the wx breaks. That is the ultimate DX antenna for 160M...

[Steve - K4HX]

Why not put up an inverted-L or wire T for the long distance stuff? You really only need to make it work on 160 meters since your dipole will likely be just as good or better for DX on 80.

[flintstone mop]

Ya Steve,
That's a very workable arrangement, that I have plans for end of Summer.
You had very good success with a "T" in Ballimore. Just needs some radials and a tuning netowrk.

Fred

[KA2QFX]

Fred,
 After reading all the posts and examining the assembly manual it's hard to determine just how this antenna functions. It looks like a J-pole but the purpose of the insulator is unclear. I can't exactly determine where the cage wires are insulated versus connected from the manual. It's academic I suppose, but I can't help but think something else is fundamentally wrong causing the need for a matching inductor and perhaps this arcing.

Nevertheless, you have a high voltage at the insulator that needs to be dealt with!

  I have Teflon, Nylon and Delrin in the sizes needed and would be glad to make the part you require if I had an accurate measured drawing.  I would suggest making the top collar of the insulator a bit longer, like 1-1/2".  Even though it has superior dielectric properties I would be leery of using Teflon because of its very poor mechanical properties. It deforms easily and has virtually NO ability to rebound to it's original dimension. 
That leaves Delrin and Nylon, either one has it's pluses and minuses amounting to a draw.

As I recall Hy-Gain usually uses a non-filled, thermoplastic much like Nylon for there plastic parts on their antenna elements.  It does not contain carbon, but they have been known to arc readily in there beam element traps.   

PM me if you're interested.  ka2qfx@comcast.net
http://home.comcast.net/~msed01/

73, Mark

[WD8BIL]

The antenna is trying to tell you something. 

Yup!
The design sucks. That point in the antenna is the electrical end of the 80 meter 1/4 wave...... all voltage.... no current! It would appear they didn't figure that in when they "designed" the insulator.

[ke7trp]

Is this antenna using the coax as the second half of the antenna like the gap?

C

[KA2QFX]

Clark,
No, this is fed like a 1/4 wave vertical.  I kinda figured this out.  On 10,15 and 20 it's clearly like a J pole. 1/4 wave open stub, end fed, give or take the capacity of the remaining radiator to bring it to resonance. On 40 and 80 it behaves much like a step-down and step-up gamma match respectively. The voltage appearing across that insulator on 80 meters is about what you'd see between the 26 and 68 degree points on a full sized 75 meter 1/4 wave element.  That difference being about 45 degrees I imagine the voltage could be appreciable.  

[Bill, KD0HG]

Wrap the insulators with Kapton film of some kind. It won't ever cold flow (if that is a concern) and a couple mils of the stuff is good for at least 10 KV. Like 3,000-6,000 volts per mil. Kicks Teflon's butt.

One thin sheet of Kapton between two aluminum plates is used in Harris FM transmitters as a plate bypass cap, and that's at 12 KV plate voltage. Supposedly hi-pot tested to 50 KV .

Kapton is Kryptonite for high voltage apps.

http://www.kaptontape.com/5_Mil_Kapton_Tapes.php

Bill

[WD8BIL]

I never thought of that Bill! Eimac used it in their 50KW 2200 series FM cavity too as a blocking capacitor. 2 wraps around the big plate of the 4CX20,000 then into the cavity tube. 10KV at 5 amps never phased it!

Good thinking Home Grown.

[flintstone mop]

I just checked back to this thread and extremely interesting comments about the Jr.
I'm attaching a picture of the Delrin material sent to me by Pat, N4LTA and Frank (The Slab Bacon) has offered to make a copy once I receive the replacement insulator.
Mark, Thank you for your offer to re-design the insulator.

Bill: The Kapton sounds really good as future material to use in situations like this.
HyGain or MFJ probably decided to downgrade whatever material was used in the original design. They want to know what success I have with the Delrin. They would be willing to change that part of the design, and they know that the instructions for the antenna are very crude and hard to follow, which causes numerous problems for the owner/builder.........they probably give up.

Fred

[WA1GFZ]

I use 3 mil kapton as a dielectric in my class E rigs to form part of the Shunt C and heat spreader insulator against the heat sink. 
Never burn kapton it will kill you.
Kapton is also used in SIL pads and transistor insulators.
Great stuff

[Gito]

Hi

Remember  the Dielectric constants  of the isolator changing the material,can change the value of the capacitance between,the top tube and the lower tube.

 And the Antenna won't behave as it should be.

Gito

[flintstone mop]

Good point Gito,
I made that discovery when I used a porcelain insulator between the top and bottom sections. The RF saw the bottom mast only and the antenna was resonant ONLY on 4.2 mhz and 40M was now at 7.7 mhz..

The only thing I could measure with the capacitance meter was 1000pf at 9 mhz. The meter gave me weird readings on the 40 and 80M freqs.

It will be interesting what the Delrin does.
Fred

[The Slab Bacon]

Phred,
         I was able to get 2 of them out of that piece of Delrin. They are going out in this morning's mail. Let me know when you get them. It has been about 10 years since I have machined that stuff, I had forgotten what a pain in the a$$ it is. I'd much rather machine metal any day!! While I was plowing down the OD, I handed my wife the end of the cutting and told her to walk with it. She got all of the way from my garage out to the front street before it turned off, over 100' of "chip"! ! ! ! ! ! I had delrin cuttings from one end of the garage to the other! 

Pat,
     That hunk of Delrin was about 3" od x a foot long. When I got finished I had a full full sized trash can full of cuttings     

[WD8BIL]

You're a good man, Slab Bacon!

[N4LTA]

Last time I machined that stuff I had half a room full and when you don't know what you are doing like me - and push the tool in too fast and it digs in  - Uh OH

Pat

[The Slab Bacon]

Last time I machined that stuff I had half a room full and when you don't know what you are doing like me - and push the tool in too fast and it digs in  - Uh OH
Pat

 

that szht is tenacious!! the cutting will catch back on itself and either ball all up around the tool bit or tool post, or ball up right back onto the work. If the cutting is heavy enough it won't break. It's nasty stuff to work with.

My machine uses 5/8" tool bits, so breaking them was not an issue. The trick is grinding the right shape onto the tool bit to spit the cutting away from it and hopefully into the chip tray. Once you get the right tool bit and remember the proper technique for that stuff, you can really plow the material off.

The real bitch was putting the hole into the center. The biggest drill that I have is 1"
So I had to drill them to 1", let them cool off and then take them to 1 1/4" with a boring bar. Drilling the 1" hole was a toughie. As you drilled it out the material would get hot and expand, If you didn't extract the drill bit quickly the material would cool down and shrink to the drill bit, making it unbearable to get the drill bit out.

All in all, they came out pretty nice, I think phred will be very happy when he sees them.
                                                                                                        

[N4LTA]

Not only a good man but a good machinist who knows what he is doing!

I have a 9x20 that I put a 1 HP motor and AC drive on - I love to play with it but have no clue as to do anything but basic turning and doing anything to proper dimensions is very unlikely. Sometimes I get lucky!

Pat

[The Slab Bacon]

Pat,
     I am totally self-taught. Many years ago I needed to find someone that could make parts for some of the antique engines that I collect. Professional machine shops were just too cost-prohibitive, so I acquired my first lathe and played with it until I could get it to do what I needed to do. That was 35 years and 3 lathes ago.

The current machine is around 100 years old! It is a W.F.& John Barnes model 13
(16" x 36") that was converted from a line shaft shop to a stand alone machine. It is in surprisingly good condx, the ways are still tight and straight and it cuts straight and true. It does have some modern upgrades and amenities but is a lot of fun to use. And besides there is definately something to be said for quick-change toolposts and indexable carbide tool bits!

I do sometimes find it relaxing and and unwinding to go out to the garage and crank out some parts. My next acquisition is going to be a milling machine.

[N4LTA]

Slab,

I love to play with the machines. I have a mini mill also but the problems that I have are in setup and knowing how to properly measure to get things to repeat. I can turn and bore OK  - but getting things measured while on the machine is where I get into trouble. 

I broke an aluminum outrigger on my fishing boat and needed to make a splice - measuring the broken tube IDs and then making a tight fit splice piece that fit to the broken pieces (two different IDs that I had to measure on a boat 250 miles away) was a major do it three times PITA. It had to be tight because they are constantly whipped and anything loose would tear itself up.

Pat

[The Slab Bacon]

Pat,
      I have used one of those small table-top milling machines before. They just don't seem to be rigid enough. They are just about impossible to find used.
I was considering one of them, but once you have used a full sized Bridgeport there is no comparison. I have found some really good deals / cheap prices on full-sized Bridgeports, but they are just too far away to go and get myself and too heavy to to even consider shipping. I have seen them go for as little as $500. I just need to find one that is somewhat local.

As far as the outrigger goes, I would have brought it back home, fitted up a plug splice and TIG welded the whole shebang back together.

[KA2QFX]

I sent another sleeve off and Fred should have it Tuesday. 

I machine between centers for synthetics longer than about 4 inches. They tend to catch and become airborne otherwise. I also turn VERY fast with razor sharp tooling.  Better than turning copper though! 

We also did some calculations. Looks like the sleeve is about 56pF for 5" of insertion. The RF current is pretty high if the voltages are as high as the previous failures indicate. It'll be interesting.

Mark