On 5 Feb 2002, at 7:36, n4lq@iglou.com wrote:
> There isn't any "safe way". Some ways are less dangerous than others.
> Use something else to tune the antenna then change over to the
> Pegasus. Palomar had a switchable noise bridge for this purpose.
>
I must respectfully disagree that it is dangerous to tune-up a Pegasus
or any other popular 100 watt transceiver. All major manufactures
provide warranties on their radios and they would have to have rocks
in their heads to produce a unit so frail that it would not withstand
the wide range of abuse the ham radio community will dream up to
see just how good their engineering departments really are! :-)
Seriously, it is not uncommon to find intermittent open or shorted
connections in our feedlines or to inadvertently transmit into the
wrong antenna and so on. These conditions hardly ever cause
failure of the PA.
The PA stage in the Pegasus is robust and well protected against
catastrophic failure modes, so don't worry about doing damage to
the finals. Someone in an earlier post said that the only protection
on a Pegasus is the fuse. Not so! Beginning with the Paragon I
believe, all TT 100 watt radios have included a current limit sensor
to fold back drive when the PA current reaches design max levels.
In my opinion this is a much better design than SWR fold-back
because it is current, not SWR that damages transistors. As I recall,
the Motorola MRF 45X series transistors were able to operate into
infinite SWR. All transistors have finite voltage and current limits
however. I know TT is now using a different transistor part number
in the PA and I don't know it's SWR rating but I'll bet it is about the
same as the Motorolas.
That said, I'm not suggesting we deliberately abuse our radios and I
agree that it is good practice to reduce power during tune, not so
much to protect the radio as to comply with FCC rule 97.313(a) and to
be considerate of others using the band.
Just follow the instructions for your tuner, use minimum power
needed and fear not! Your Pegasus will live a long and healthy life
and your stress level will be much lower. Hey..........this ham radio
stuff is supposed to be fun!!!! :-)
-73-
-Lee-
|