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!
Cheers, Jim Moritz
73 de M0BMU
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Dick
Sent: 11 June 2006 21:51
To: [email protected]
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.
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