From: "Malcolm Watts"
Date: Fri, 27 Oct 2000 08:30:29 +1300
Subject: Re: [TSSP] Spoiled Q
Hi Richard,
Interesting you should say this:
On 25 Oct 00, at 23:40, RMC wrote:
> If the Q is being spoiled by the small % volume of dielectric, then
> maybe it is the absolute electric field intensity that is responsible
> for promoting polarisation losses in the coilforms. This would be
> significant for any polar molecules present, namely water absorbed
> into these sonotube forms.
>
> The deteriorated Q will effectively look like significant shunt
> conductance. the problem with that is that the transmission line
> equations (root L/C for starters) are no longer valid, because it is
> assumed that G=R=0 ( should be root (L+R/G+C). The Tx line is usually
> studied for low loss cases where conductance between conductors, and
> resistance within conductors, is small. In this case, the ability to
> solve for a specified coupling per unit length dx must be modified.
> The attenuation constant alpha will not tend to zero, and the result
> is that the resonator no longer looks much good: low Q!
My 10" PVC drainpipe secondary once gave an interesting set of
readings on two consecutive days. The first was a relatively
dry day and Q clocked in at 320. The subsequent day was a high
humidty one and the measured Q had deteriorated to just under
300. If moisture was being absorbed by the PVC (anecdotes say
that PVC does that) then it would have been absorbed by the
inner wall as the outer wall was varnished. Perhaps though the
atmosphere alone was resonsible?
Regards,
Malcolm
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.