TEFLON Insulator

[The Slab Bacon]

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!  
Mark

Ah, yes, thats called a PWANG! !     Been there, had that years ago.

I also do as much as I can between centers. But it's kinda tough to bore it out with the tailstock in your way. I friggin hate machining copper.

I sent mine out in yesterdays UPS, He'll prolly get them monday or tuesday.

[WA1GFZ]

Frank I just did a 1/4 inch copper heat spreader. I had to drill and tap 20 4-40 holes. I had some ATF in the oil can after my yearly squirt of the body joints of the truck.
It seemed to work well for tapping. I do go very slowly and never rotate a full turn because I'm chicken to snap a tap.

[The Slab Bacon]

Frank I just did a 1/4 inch copper heat spreader. I had to drill and tap 20 4-40 holes. I had some ATF in the oil can after my yearly squirt of the body joints of the truck.
It seemed to work well for tapping. I do go very slowly and never rotate a full turn because I'm chicken to snap a tap.

Tap Magic helps, but back the tap ALL the way out frequently and blow out ALL chips from both the tap and the hole or you'll be hatin life! ! ! !

[KL7OF]

have you seen the taps with the DEEP grooves?  Don't require as much back peddling as a standard tap..They might be weaker tho...They are designed for use in a powered tapping gun.  Work FB for hand tapping

[flintstone mop]

This will be interesting to see how this new approach with different material will hold up. The capacitance created by different material  and being able to slide the upper mast in and out of the lower mast will make for some good experimentation. I better run AC out there to power up the MFJ 269. They eat batteries alive, even when they sleep (SLP)
Thanks Mark and Frank...NOW watch it turn colder than a witches #*^
Fred

[flintstone mop]

DAM Frank...........................you're good!!!
Pics to follow. I'll edit this with a picture of your work.
The Delrin pieces look really nicesh.

Mark is sending a unit made from Teflon. I hope the WX is ready for this weekend.

I'm ready>................
Fred

[The Slab Bacon]

The Teflon is probably a better insulator, but the Delrin is harder and has a little more mechanical strength and ridgidity. It should be an interesting comparison / compromise as to which is "better".

With the amount of machining involved with making them from "rod stock" on a manual machine, it is very easy to understand why they make them out of "injection molded" materials. It's just downright cheaper to do it that way.

With the way that the cuttings ball up around the work and the tooling, I dont think you could do them on a CNC machine. It would have no way of knowing how to compensate for the ball of cuttings and how or when to remove it. I had to stop many times in mid cut to manually cut away the cuttings that would ball up around the workpiece and the tool bit. A real PITA....................

[KA2QFX]

Out of curiosity I looked up the electrical properties teflon vs. the delrin. It seems the teflon has a dielectric constant of 2.4 and the Delrin is 3.7. Also, the resisitivity of the delrin is almost double that of teflon. Seems like delrin, being much stronger as well, is clearly the winner in this application.

[The Slab Bacon]

Out of curiosity I looked up the electrical properties teflon vs. the delrin. It seems the teflon has a dielectric constant of 2.4 and the Delrin is 3.7. Also, the resisitivity of the delrin is almost double that of teflon. Seems like delrin, being much stronger as well, is clearly the winner in this application.

Wow, interesting, Mark. I would have surely thought the Teflon would have had better insulating properties than the Delrin. I just know that it is physically softer than Delrin.
(and has a tendancy to "cold flow") If you have to buy the stuff outright from a supplier, I wonder which is cheaper? ? I would imagine that the Teflon could handle higher temperatures without burning. The Delrin, other than it's tenacity and tendancy to ball the cuttings (cant really call them "chips") up around everything,basically"feels" like most other common plastics when you machine it.


IIRC, a few posts back Phred said something about trying to use Porcelain insulators, but the antenner wouldn't tune up properly. I wonder how much different the insulating / electrical properties are between Delrin and Porcelain?

It would also be interesting to know what exactly that black plastic moulded factory insulator is actually made of. (Since most black dyes are made from lamp black which is actually carbon)?

[KA2QFX]

I'm pretty sure there's no lamp black being used for dying plastic these days. At least I haven't seen anything affected in the uWave.  But the Delrin ain't cheap either. I believe the advantages of Teflon are, as you say, it tolerates high temperatures well and we used to use a lot of it in chemical analysis and synthesis systems because it handles solvents well and is generally non-contaminating.  The cold flow is a problem because it's also non-resilient. Makes a great valve seat, but only lasts a few closures before it's paper thin.

I'm trying to model this antenna now using EZNEC. I have some definite suppositions on how it works but it would be nice to nail down some of the variables Fred is dealing with.  I've only roughed out the 75 meter configuration so far but it shows the insulator current being nearly zero. Which according to this modeling indicates a substantial voltage is likely.

I think the porcelain insulator was preventing inserting the two masts together so no capacitor was being formed.

Finally, when turning large plastic pieces I find a shop vac will suck off the long turnings quite nicely. It seldom breaks the ribbon and never lets it slack and accumulate.   I have an old spring clamp from a broken work light that I use to hold the 2" shop vac hose on the cross slide.  Works for cast iron (yechh) too.

Mark

[flintstone mop]

Hello Ladies and Gentlemen
The jury is still out on the insulator that will not arc on this 18HTJr HyGain antenna.
Mark, I will send you lengths of the elements in a separate email. Mine are slightly different from the manual, which is a downloadable PDF from HyGain. I'll send a link for that too later.

But, as promised are pics of the insulators. The black one is the original from HyGain, and the taller Delrin piece is Mark's. The shorter is an exact copy of the HyGain made by Frank, The Slab. Both pieces are a work of art. Then, there is a top view of the replicas.
I will report on the tuning difficulties that happened and the big test of legal limit RF on 80M.

Fred

[KA2QFX]

Mark, I will send you lengths of the elements in a separate email. Mine are slightly different from the manual, which is a downloadable PDF from HyGain. I'll send a link for that too later.

Aha!  How interesting!  I finished the model as per the manual and added what I presumed to be the "aluminum strips" lengths.  Regardless of my tweaking I could not get it to resonate below 3.750 with the parameters as is. It will be interesting to see what the modified lengths will do.  

It did however hold true to theory, that at resonance a shortened antenna presents a much reduced radiation resistance (real part of the Z). In this case, R was about 10 ohms at resoance. At 50 ohms, X was almost -90. Either way, without some external matching (or significant losses in the antenna) SWR will be quite high.  All of which of course isn't very relevant to the insulator frizzling.

I love this antenna stuff!  If anyone uses EZNEC I'll gladly share the params file if you let me know.

Mark

[The Slab Bacon]

I was going to make a "modified" insulator, but there was some mention of the stray capacitance causing a tuning issue, I elected not to. Also the length of the piece of Delrin that Phred sent me was exactly enough to make 2 of them without any room for waste. So................I made 2 exact copies of the original one. I had exactly enough left to grab it in the lathe chuck with none to spare. I was just missing the chuck jaws with the tool bit.

I have since found a source for Delrin rod stock in sizes that would save a lot of machine work if we ever have to make more of them. They are 1 1/2" OD and 1 1/4" ID, I plowed those out of 3" stock, which put most of the material in the chip tray / trash can / garage floor.

The proof of the puddin is the eatin, now we need to know how they worked.........

[flintstone mop]

Hi Mark and Frank
Mark, the element lengths for 20-10M are independent of 80 and 40M. They may influence 80 and 40 somewhat, but shouldn't be a 'make or break' situation.

I have noticed that 80 and 40 interact a little with each other. 40M is less affected but depends on that extra length of mast above the insulator.
80M is very sensitive to everything, it seems.

Frank I emailed Mark this info that I now get a weird problem that when 600W is applied to the antenna the forward power starts to drop and the SWR rises slowly.
Bird Watt meter readings. I wait a few minutes and I can go through the whole cycle again. 600W for a few seconds and then drops off and SWR increases.
I'm going out to the antenna to take pics of whatever is failing or heating. Arcing usually shows up as very erratic SWR spikes and once arced, I would only be able to input 100 W and then instant short, or SWR skyrockets and amplifier very unhappy. So, I'm taking very slow steps increasing power until the matter is settled. I don't want to mess my AL1500 up with this dumass antenna.

Fred

[The Slab Bacon]

It sounz like something is heating up and going up in resistance. (loose connection) Unfortunately, I am not at all familiar with yo antenner.

Sounz like yo got to give her a real careful eyeball exam / look over. Get yer magnificant glass out and sherlock it up a bit.

What happenz when you hit her with a little munky swingage? ? At 600w, some munky swing should tell the tale. Sometimes you got to hittem real hard to really show up the problem. If you are gettin arcage and burnage, I dont think it would go back to "normal" after it cools down.

[Steve - K4HX]

The antenna is trying to tell you something.

[WQ9E]

I think you will soon find the next weakest link in the antenna (and there may well be more beyond the next).

[flintstone mop]

The antenna is trying to tell you something.

hmmmmmmmm I think I read this somewhere before..
I know, I know, I might as well get one of those 43 foot wonders with a balun and there we are. Hassle-free and no tuner needed. HA!

[The Slab Bacon]

Phred,
         After our phone conversation, I have given this much more thought. I am starting to think the problem may just be the actual thickness of the sleeve. At 1 1/2" OD and
1 1/4" ID, that leaves you with 1/4" difference, or + 1/8" wall thickness. If this is a very high voltage point of the antenna, I kinda wonder how much voltage (or RF) 1/8" of plastic will take without "punching through". I'm starting to think a mechanical redesign is in order to accomodate a considerably thicker insulator, as well as an electrical redesign to compensate for the change in capacitance of the thicker insulator.

Or possibly turning a new sleeve out of some type of super ultra high grade insulating material like Kapton. Although I would dread the thought of what that stuff would cost, if you could even get it in rod stock.

(The gears in my head are grinding)

[flintstone mop]

Vee Vill defeet this evil antenna!!!
When we get back to Spring temps, I'm going to look at the original porcelain cup idea and an actual fixed value vac cap and start to just 'play around'. Beings that we kinda figured out a capacitive coupling between masts.
I still have the section that was cut and modified to allow for the porcelain cup, to maintain the original lengths of the loading wires.
Why others may not be having problems, is that they are installing these antennas as, recommended by HyGain. Just a ground rod.
One Ham in Mississippi just uses a ground rod. He says ground conductivity is outrageous there. He DID have the arcing problem, but fixed it by opening the bottom of the replacement insulator to let water or condensation drain through. But he is only running 1KW input on SSB. He's not stressing the insulator as I would under AM mode. So, back to the HUZMAN telling me that the antenna is saying something, means, "REDUCE power a little and we'll be friends??"
I have the K1MH, radial system using the vinyl covered, welded fencing. 7 of 'em. 50 feet long and 3 feet wide evenly spread about the base of the aerial and bonded together to a ground rod and the shield of the coass.

Here's some pictures of a bad melt-down.........and the joint was still warm after many minutes of no RF power. It was cloudy and only 30 F. It musta got HOT out there. When the SWR was showing constant short I stopped transmitting.. ALWAYS carefully ramping up or down power to protect the amp from sudden bad things that were going on out there. I cannot depend on my wife to hit the PTT when I give her instructions using a cell phone and I'm out at the antenna looking for the failure or listening for arcing. She would not understand all the meter readings and when to stop PTT. So, I let her rip and do some bad stuff so I can see the real crap going on out there.

I just discovered this link and wonder if it's the same principle used in the GAP antenna.
http://www.gapantenna.com/superc_how.htm

fred

[KA2QFX]

It's likely not the voltage but the current. 

[flintstone mop]

I ordered a Ruskie vac variable and going to do the porcelain beehive trick between the two masts. The cage wires and some JB weld will hold the upper mast in place with no problem. I did this before. And connect the 25kv cap between the two masts for the coupling. And tweek the cap until antenna is back to spec. Hopefully the real value lies between 5 and 100Pf
The Russian vac caps are really nice. This one is NOS.

http://www.ebay.com/itm/330498758654?_trksid=p5197.c0.m619

Fred