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From: "james moritz" <j.r.moritz@herts.ac.uk>
To: <rsgb_lf_group@blacksheep.org>
Date: Mon, 12 Jun 2006 14:34:55 +0100
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Subject: LF: RE: Re:PA4VHF/p TX problems
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Dear Dick, LF Group,

The Siemens/Epcos N30 material is a high permeability ferrite specified =
for
EMC suppression purposes. The saturation flux density is somewhat lower =
than
materials like 3C85 etc, but probably the main problem will be the =
higher
core losses. The flux density due to the primary winding inductance =
works
out to around 100mT with 500W TX pwr, which might get close to =
saturating
the core at high temperature. It will certainly cause considerable power =
to
be dissipated due to the losses in the core. The Epcos data does not =
specify
the core loss (core not being used for its intended purpose - high =
losses
are an advantage for a "suppression" ferrite), but it must be at least
several watts, which would certainly make the core get hot.

A possible reason for the antenna current not increasing is corona, =
which
can be a real problem with a small antenna - as the voltage increases, =
the
power loss in the corona discharge gets higher, which leads to increased
antenna loss resistance, which prevents the current from rising much - a
kind of self-limiting effect on antenna current. I used to get this when =
I
started running QRO on LF. The corona can be hard to detect, but the =
usual
tell-tale sign is that something catches fire eventually!=20

Cheers, Jim Moritz
73 de M0BMU

-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org
[mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Dick
Sent: 11 June 2006 21:51
To: rsgb_lf_group@blacksheep.org
Subject: LF: Re:PA4VHF/p TX problems

First off all thanks to Mal and James for picking up my signals.
Thanks Alan for your comments.

Well, I did tune the system with the help of a low power TX before =
running
high power.

I think the problem might be caused by the step up transformer I used to =
go
from 50 to 150 Ohm,
before coupling into the vario meter.