Re: Wave guide dummy load.


John E. Beech
 

There is an attenuator for 10 GHz in the said book (below) which consists of a piece of card scribble all over with soft
graphite pencil to make a thin (poorly ie lossy) conductive layer - basically a spresd out carbon film resistor.

Mixing carbon with epoxy resins does strange things. I once bought a pocket chess set for my son with a missing black
pawn. I cast one in epoxy resin using carbon as a filler & colourant. It never set hard and remained rubbery. I suspect a
lot of the cross links in the thermoset resin were mopped up by the carbon & became dead ends ie not linked to anything
else.

de John G8SEQ

-------Original Message-------
From: KENT BRITAIN <WA5VJB@FLASH.NET>
To: ukmicrowaves@groups.io <ukmicrowaves@groups.io>, UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] Wave guide dummy load.
Sent: Mar 04 '21 02:02

Only, Only if there is enough Carbon to make the epoxy electrically
conductive.
The particles have to be touching. A little Carbon does nothing. Kent

On Wednesday, March 3, 2021, 07:22:13 PM CST, Gordon REASON via
groups.io <gordonj.reason=virgin.net@groups.io> wrote:

would'nt some carbon powder , mixed into one part of an epoxy , such
as araldite , have a good absorbtion >>>>> just thinking !
> On 03 March 2021 at 19:18 "John E. Beech" <john@g8seq.com> wrote:
>
>
> Tnx John,
> I eventually found it on page 8.20 of the 1969 edition. No mention
of it in the index under micro- or wave-
> though.
>
> de John G8SEQ
>
> > -------Original Message-------
> > From: John Fell <john.g0api@gmail.com>
> > To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
> > Subject: Re: [UKMicrowaves] microwave absorbent adhesive polymer?
> > Sent: Mar 03 '21 10:57
> >
> > RSGB VHF Manual - Microwave section .Wood in guide dummy load .
> >
> > John
> > G0API
> >
> > On Wed, 3 Mar 2021 at 10:11, John E. Beech <john@g8seq.com>
wrote:
> >
> > > Don't laugh, but has anyone tried a thin strip of balsa wood or
> > > plywood for the absorber? ( Perhaps covered in
> > > graphite pencil lead?) I once made an effective waveguide dummy
> > > load for 10 GHz out of wood - a specially shaped
> > > wedge. I don't know where the design came from but I got it
from
> > > G8MWR (SK).
> > >
> > > de John G8SEQ
> > >
> > >> -------Original Message-------
> > >> From: Neil Smith G4DBN <neil@g4dbn.uk>
> > >> To: BVA-transverters-uk@groups.io
> > > <BVA-transverters-uk@groups.io>, UKMicrowaves@groups.io
> > > <UKMicrowaves@groups.io>
> > >> Subject: [UKMicrowaves] microwave absorbent adhesive polymer?
> > >> Sent: Mar 02 '21 23:27
> > >>
> > >> Are there any secret sources of microwave absorbant material
> > > which will
> > >> work from 2.5 to 10 GHz with good reflection loss and bulk
loss,
> > > around
> > >> 1mm thick and self-adhesive?
> > >>
> > >> For the F6BVA 3cm to UHF transverters, we need a bit about 150
x
> > > 50 mm.
> > >>
> > >> I see RF Microwave has some at around £330 for a 600 mm
square
> > > sheet of
> > >> silicone 1mm carbonyl/iron, which makes 48 pieces at around
> > > £8.50 per
> > >> piece including VAT etc. The price from Mouser etc for similar
> > > stuff
> > >> works out about the same. Is that the right sort of price or
is
> > > there
> > >> some low cost magic stuff of which I am unaware? The gap above
> > > the PCB
> > >> is only 7mm, and some of the components are a few mm tall, so
> > > 1/16" or
> > >> about 1.5 mm is the max I can fit in.
> > >>
> > >> Neil G4DBN
> > >>
> > >>
> > >>
> > >>
> > >>
> > >>
> >
> >
>
>
>
>
>

Join UKMicrowaves@groups.io to automatically receive all group messages.