The AM Forum

Lexan appears to be mechanically superior.  Plexiglass tends to be brittle and cracks easily, and if proper precautions are not taken, may shatter when sawed or drilled.  Lexan seems to be almost malleable like metal.  It can be bent and drilled cold and seems practically indestructible. It is used commercially for making bullet-proof vests, for example.

But I am not sure about two other characteristics: resistance to UV damage, and RF dielectric properties.

Looking at several websites of vendors and manufacturers, I have noticed that polycarbonate may or may not be specified as "UV protected".  I have some sheets sold as replacement window panes, and the paperwork that came with them specified "UV protected on both sides".  This seems to imply that polycarbonate may not be inherently immune to UV damage, but that it may be made resistant by adding some additional ingredient to the plastic itself, or by applying a special coating to the surface.  Plexiglass is inherently unaffected by UV; it was specifically developed shortly before WWII just for that purpose, for use in aircraft windows. On one of the plastic vendors' websites, they specified that Lexan has proved resistant to UV for "5 years or more".  This implies that it may eventually succumb to self-destruction in outdoor environments. The plexiglass spacers I used for my open wire feedline that goes up the tower have been exposed to the sun and weather for nearly 30 years with few signs of deterioration.

As far as RF insulative properties are concerned, I have heard it said that Lexan is a better RF insulator, but the only technical data I have been able to dig up regarding electrical characteristics give both Lexan and Plexiglass about the same dielectric constant at 1 mHz, and say nothing about rf loss characteristics.

Lexan is somewhat more expensive, but would be worth the extra expense when making such things as antenna insulators and open wire spreaders due to its superior mechanical strength and malleability, if it can be expected to hold up indefinitely in an outdoor environment. I don't think the RF loss in plexiglass is ideal, but it is still much better than other plastics like PVC, or wax impregnated wood, but if Lexan really does has lower RF loss that would be a plus as well.

Thick sheets of Lexan appear to be very expensive.  McMaster-Carr sells 12"X12" sheets of clear smooth polycarbonate @ about $26 for 1/2" thickness, but for 1" thickness the price goes up to about $165!

The latest QST has an article about a window line dipole insulator made from polycarbonate.    He states it is immune to UV and I suppose it is OK for RF considering its use.

A piece of lexan from the hardware store had protective paper on it and it stated "this side UV protected" so it must use a coating to accomplish it. I use it for a little security camera window above the garage door. After 10 years it seems OK.

I have the support insulator for the center element on my HyTower copy vertical made from 1/4" Lexan.  It's been up for quite some time without any visible UV damage.  The stuff doesn't seem to be bothered by RF in the least.  I've taken down old Lexan sign faces which have been in the weather for years and repainted them for reuse.  Works great for antenna insulators.

A few weeks ago I ran across a center insulator and both end insulators I had used for 80M in the 60's thru mid 1989. About 1/2" thick and Im pretty sure it was some scrap Lexan I used. They still look OK and Im planning to use them for a low 80M antenna.

Im using 1/2" Delrin currently for the center on the high antennas and thats been up since 1990.

Carl

Don,
Some 30 years ago I made up spacers for my open wire line out of 6" pieces of 3/8" Lexan rod stock.  It looks as good as the day I put it up.  None have broken over the 30 year period.  Good stuff in my book.
Regards,
Joe, W3GMS

Plexiglass, (acrylic) dissolves nicely in acetone. It can be applied with a small paint brush as an insulator for coils. I used this method to repair a B&W 850A I bought that the separators disintegrated.

It can be used to "weld" pieces together as well.  The dissolved surface layers of both pieces mix together, and when dry, form a single solid piece that is just as strong as an original solid piece.

Sawing plexiglass can be a real PITA.  I quickly found that using an ordinary jigsaw would not work.  The blade quickly heats up and leaves behind a trail of melted plastic, which solidifies and re-welds the pieces back together.  About all the saw ended up doing was to make a heavy white line in the plastic where the cut was supposed to  be.  But if the blade is water cooled, the saw works fine.  I use a garden hose just barely turned on so that a small stream of water flows.  The stream is directed to the blade just where it enters the plastic, and a small puddle is allowed to accumulate on the surface. That keeps the blade cool and it cuts right through the plastic leaving a smooth, almost polished edge on the two pieces following the cut.

Of course, this has to be an outdoor project, since the reciprocating saw blade splashes and sprays water all over the place.  Expect to  get soaked in the process.  The water doesn't seem to hurt the saw.

I machine lots of parts from plastics, Lexan and Delrin are two of my favorties. IMHO Lexan is 10 times the material plexiglass is.  The only benefit to plexi is it polishes easier for indoor displays.
My mobile antenna has been exposed to direct sun for over 20 years with no sign of deterioration. All the clear plastic here is Lexan.

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