Wow, I'm amazed you put Teflon and nylon in the same category! There
are many types of nylon, and AFAIK, none is particularly low loss.

One reference I have suggests a dissipation factor for polymethyl
methacrylate (unadulterated "Perspex") of about .008 at 3GHz. Nylon 66
(a common formulation) seems to be about three or four times that much.
But beware that you commonly don't get "pure" plastics.

For comparison, Teflon runs more like .00015 dissipation factor at
3GHz. Pure forms of polyethylene and polystyrene are similarly low.
Polypropylene tends to be good, below .001. Polycarbonate is decent at
around .002.

Cheers,
Tom


Risto Tiilikainen wrote:
Martyn Preston kirjoitti:
Does anyone know how lossy perspex is at 2.3GHz? Want to use it to support a
helical antenna.

TIA - G0THY


Hi

I wouldn't try perspex nowadays
Perspex itself is very lossy when compared to modern compounds
I think perspex absorbs easily humidity and then you may have problems.
Specially in voltage maximum points of helical.
For the same reason I don't recommend fiberglass for outdoor use.

I recommend Teflon or nylon for insulators and supports.

73, Risto OH2BT

K7ITM wrote:
Wow, I'm amazed you put Teflon and nylon in the same category! There
are many types of nylon, and AFAIK, none is particularly low loss.

One reference I have suggests a dissipation factor for polymethyl
methacrylate (unadulterated "Perspex") of about .008 at 3GHz. Nylon 66
(a common formulation) seems to be about three or four times that much.
But beware that you commonly don't get "pure" plastics.

For comparison, Teflon runs more like .00015 dissipation factor at
3GHz. Pure forms of polyethylene and polystyrene are similarly low.
Polypropylene tends to be good, below .001. Polycarbonate is decent at
around .002.

But be sure to pay attention to UV susceptibility if your antenna is
exposed to the sun. Many plastics deteriorate quickly in sunlight, and
polypropylene is particularly bad. And of course you might need to
consider mechanical properties. Polystyrene is brittle and breaks quite
easily. Polyethylene and Teflon are soft, and Teflon cold flows. (I
don't know about polyethylene but suspect it might also.) Polycarbonate
is tough and nice stuff mechanically, but don't know about its UV
resistance.

Roy Lewallen, W7EL

Roy Lewallen wrote:
K7ITM wrote:

Wow, I'm amazed you put Teflon and nylon in the same category! There
are many types of nylon, and AFAIK, none is particularly low loss.

One reference I have suggests a dissipation factor for polymethyl
methacrylate (unadulterated "Perspex") of about .008 at 3GHz. Nylon 66
(a common formulation) seems to be about three or four times that much.
But beware that you commonly don't get "pure" plastics.

For comparison, Teflon runs more like .00015 dissipation factor at
3GHz. Pure forms of polyethylene and polystyrene are similarly low.
Polypropylene tends to be good, below .001. Polycarbonate is decent at
around .002.


But be sure to pay attention to UV susceptibility if your antenna is
exposed to the sun. Many plastics deteriorate quickly in sunlight, and
polypropylene is particularly bad. And of course you might need to
consider mechanical properties. Polystyrene is brittle and breaks quite
easily. Polyethylene and Teflon are soft, and Teflon cold flows. (I
don't know about polyethylene but suspect it might also.) Polycarbonate
is tough and nice stuff mechanically, but don't know about its UV
resistance.

Roy Lewallen, W7EL
I can speak to polycarbonate in a very small way: PCB ophthalmic lenses
are treated to provide excellent UV protection. But my understanding is
that pure PCB is not particularly UV resistant. Without a coating
(which provides the UV protection) it scratches very easily, so in that
sense, it is a soft material.

John
AB8O

Roy Lewallen wrote:
K7ITM wrote:
Wow, I'm amazed you put Teflon and nylon in the same category! There
are many types of nylon, and AFAIK, none is particularly low loss.

One reference I have suggests a dissipation factor for polymethyl
methacrylate (unadulterated "Perspex") of about .008 at 3GHz. Nylon 66
(a common formulation) seems to be about three or four times that much.
But beware that you commonly don't get "pure" plastics.

For comparison, Teflon runs more like .00015 dissipation factor at
3GHz. Pure forms of polyethylene and polystyrene are similarly low.
Polypropylene tends to be good, below .001. Polycarbonate is decent at
around .002.

But be sure to pay attention to UV susceptibility if your antenna is
exposed to the sun. Many plastics deteriorate quickly in sunlight, and
polypropylene is particularly bad. And of course you might need to
consider mechanical properties. Polystyrene is brittle and breaks quite
easily. Polyethylene and Teflon are soft, and Teflon cold flows. (I
don't know about polyethylene but suspect it might also.) Polycarbonate
is tough and nice stuff mechanically, but don't know about its UV
resistance.

Polycarbonate sheets in many sizes are found in do-it-
yourself stores as window glass replacement. While
expensive, most of those brands are marked "sunlight
resistant."

Lowes, Home Depot, OSH all carry polycarbonate "window
replacement" pieces here in southern California.

On 4 Oct 2006 17:44:57 -0700, "
wrote:


Roy Lewallen wrote:
K7ITM wrote:
Wow, I'm amazed you put Teflon and nylon in the same category! There
are many types of nylon, and AFAIK, none is particularly low loss.

One reference I have suggests a dissipation factor for polymethyl
methacrylate (unadulterated "Perspex") of about .008 at 3GHz. Nylon 66
(a common formulation) seems to be about three or four times that much.
But beware that you commonly don't get "pure" plastics.

For comparison, Teflon runs more like .00015 dissipation factor at
3GHz. Pure forms of polyethylene and polystyrene are similarly low.
Polypropylene tends to be good, below .001. Polycarbonate is decent at
around .002.

But be sure to pay attention to UV susceptibility if your antenna is
exposed to the sun. Many plastics deteriorate quickly in sunlight, and
polypropylene is particularly bad. And of course you might need to
consider mechanical properties. Polystyrene is brittle and breaks quite
easily. Polyethylene and Teflon are soft, and Teflon cold flows. (I
don't know about polyethylene but suspect it might also.) Polycarbonate
is tough and nice stuff mechanically, but don't know about its UV
resistance.

Polycarbonate sheets in many sizes are found in do-it-
yourself stores as window glass replacement. While
expensive, most of those brands are marked "sunlight
resistant."

Lowes, Home Depot, OSH all carry polycarbonate "window
replacement" pieces here in southern California.

Those materials are apparently coated for UV protection. I put some
in the windows of a playhouse I built for my granddaughter and the
protective film was labeled as to which side should be out.

thanks for the replies and advice- am going to try the microwave oven test.

martyn g0thy

Report back please...


On Thu, 5 Oct 2006 08:27:23 +0100, "Martyn Preston"
wrote:


thanks for the replies and advice- am going to try the microwave oven test.

martyn g0thy

Martyn Preston kirjoitti:
thanks for the replies and advice- am going to try the microwave oven test.

martyn g0thy


Hi

Before you test perspex immerse the test piece in water for some days.
Maybe this simulates rainy days.


73, Risto OH2BT