[GreenKeys] On PVC poles

[hwhall at compuserve.com]

There's a difference, I feel sure, between heating effects at microwave wavelengths and those of the shortwave bands. Hams have been using PVC for antenna components for a long time without widespread reports of melting down or massive inefficiency.
Also, we accept losses in feedlines of a dB or so, so why fret a great deal over a little loss in the antenna coil support? Mostly, we have power to waste in transmit, and mostly we aren't concerned with digging the last few milli-microwatts of signal out of the noise on receive.
"Build it and it will work.... sorta!"   :-)

WayneWB4OGM

-----Original Message-----
From: Dave Wade <dave.g4ugm at gmail.com>
To: 'Dave Horsfall' <dave at horsfall.org>; GreenKeys at mailman.qth.net
Sent: Fri, Jul 17, 2020 12:53 am
Subject: Re: [GreenKeys] On PVC poles

Dave,
The first reference I found was in the November 1995 Radcom, in G3SEK's "In
Practice" where he suggests winding a coil and seeing if the plastic alters
the "Q" at the intended frequency, and to only use the Microwave if you
don't have a "Q" meter.
Apparently "debate" continued on usenet until March 1996, so just a short
one.
Dave
G4UGM

> -----Original Message-----
> From: greenkeys-bounces at mailman.qth.net <greenkeys-
> bounces at mailman.qth.net> On Behalf Of Dave Horsfall
> Sent: 17 July 2020 04:51
> To: Greenkeys <greenkeys at mailman.qth.net>
> Subject: [GreenKeys] On PVC poles
> 
> (Somewhat on topic, as I did use "glass" RTTY[*] some years ago, and am
> trying to find room for a real one).
> 
> I have a need to make a helical (easily concealed etc), but I am somewhat
> baffled by "common knowledge" so I figured that this list is the best
resource
> :-)  A magnetic loop is too directional for my tastes, as is also far too
high-Q
> i.e. needs to be re-tuned if you shift by a just a few kHz.
> 
> Metal is obviously right out, and I understand so is wood (because of its
> water content), so I thought about a length of PVC pipe with the helical
> wound around it.
> 
> Now, herein lies the tale...
> 
> Apparently PVC pipe may or may not contain carbon, and the only way to
> find out (apart from deciphering the manufacturer's code) is to place
piece of
> it inside a microwave oven (with the wife not looking) with a glass of
water to
> act as a dummy load to protect the magnetron.
> 
> If the PVC is warm, it contains carbon and is therefore unsuitable...
> 
> So, what is the veracity of this claim?
> 
> [*]
> And yes, I know about the CR/LF problem, as with 72 columns.
> 
> -- Dave VK2KFU
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