rf transparency of plastic

[flippineck]

I am trying to cook up a simple collinear antenna for 1800 MHz and one for 800 MHz.

I'm following plans which involve bending coils into copper wire and then enclosing the copper wire inside a length of white pvc electrician's conduit.

the plans are for 2.4GHz though. they regard the pvc conduit as transparent to the 2.4GHz signal, it's just there for protection & to give rigidity.

is white pvc electrical conduit, the kind sold by sparkies factors everywhere in the uk, 16mm internal diameter, as transparent to 800 & 1800 MHz as it is to higher frequencies?

or should I use different materials for the casing

 

[(*steve*)]

In the past I've done this and PVC does attenuate the signal somewhat, but not so significantly that I removed it.

I used pvc water pipe as it was slightly thinner.

 

[davenn]

as transparent to 800 & 1800 MHz as it is to higher frequencies?

Maybe meant to lower frequencies ? it gets worse the HIGHER in freq you go

Dave

 

[(*steve*)]

Yeah, I read it backwards. Somehow I read that it was transparent for 800/1600 and the question was "what would it be like at 2.4GHz?"

I can tell you that it's definitely not completely transparent to 2.4GHz, but as Dave suggests the loss will likely reduce significantly with frequency.

 

[flippineck]

thanks guys, so i should be ok then

these are the plans i'm working off

http://martybugs.net/wireless/collinear.cgi

but am using wavelength 16.65cm for 1800MHz and 37.47cm for 800MHz

I read somewhere that the loops are actually "quarter wave delay lines" designed to feed each half-wave straight section in phase.

so should I try to make the circumference of each of the loops, a quarter wave..

i.e. loops of diameter 2.98cm for 800MHz and 1.33cm for 1800MHz

or, should I just keep them at about 15mm diameter regardless of frequency? like the 2.4GHz plans say?

and.. if I did need to make the loops/helices longer, could I coil them up further like a short spring to make them fit inside the conduit or do they definitely have to be just one single turn (in which case I'll need wider conduit for 800MHz?

reason for all this is my mobile broadband coverage again. they've just turned on the LTE/4G signal & it's just about working using the existing 2100MHz yagi pointed in the wrong direction.. but since I seem to be in a "confusion spot" (6 or 7 towers around me, none too close, all in different directions.. the router can't choose and is being very promiscuous lol) I figure an omnidirection antenna with a bit of gain for the right frequency would be ideal.

the carrier is a bit secret about the frequency they're using but, they're licensed for those 2 frequencies so I figure it must be one or the other