Folks there's two things to consider with regard to SWR. One being a load
the is much below 50 ohms and the 2nd is a load the is much above 50 ohms.
Now, should the load be greater than 50 ohms, say 250 ohms, then the SWR
5:1. This condition will not cause the PA transistors to draw excessive
current thus likelihood of damage is nil. On the other side, if the load is
say 10 ohms then the SWR again would be 5:1 but the PA current would likely
be quite high Here Tentec uses a current monitor circuit, unlike other
radios that use a SWR monitor circuit, and a reduction in current to the PA
will occur. This is the one reason that Tentec radios do not fold back
power with high SWR values.
While it is not advisable to operate the radio with a SWR of 3:1 or greater,
one must know if the SWR is caused by a very low impedance load or a high
impedance load. One causes no reason for concern with the other will simply
require the radio to reduce current to protect the PA devices. That is
handled by the ALC circuit in the driver stage.
To prove my point, I just turned my Omni VII on with no antenna connected.
In Tune mode transmit the SWR was basically infinity to 1. The supply shows
current was about 8 amps. With the output shorted, the current was about 12
amps and again SWR was basically infinity to 1. PLEASE NOTE: Don't try
this with you non-USA manufactured radio unless you obtain a RA from the
service depot first.
Regardless of the circumstances, it is always advisable to provide some
external current limiting method, be it a very fast acting circuit breaker
or a power supply with internal current limits.
73
Bob, K4TAX
----- Original Message -----
From: <n4dxi@aol.com>
To: <tentec@contesting.com>
Sent: Friday, September 21, 2007 8:44 PM
Subject: Re: [TenTec] (no subject)
>I don't know about the Paragon but most modern transceivers have a self
>limiting feature; if high swr, the feature minimizes rf being transmitted
>thus protecting itself.?
>
> For brief moments, a high swr should not be catastrophic.
>
> It could have been worst...like transmitting when there is no antenna
> connected!? Or transmitting into a shorted cable.
>
> 73...John, n4dxi
>
>
> -----Original Message-----
> From: john ferro <foxbat426@hotmail.com>
> To: tentec@contesting.com
> Sent: Fri, 21 Sep 2007 7:57 pm
> Subject: [TenTec] (no subject)
>
>
>
>
> hi ten tec gurus! hope all is well - quick questions - i forgot that my
> radio
> (Ten Tec paragon)was tuned to 17 meters and for a split second talked into
> the
> mic a full power (100 w)on 20 meters - the swr went to about 5 or 6:1 for
> a
> click of a mic second or two - this is the second time i did this
> (stupidity) -
> wondering if this can do damage? - obviously its not good. the radio seems
> to be
> fine and didn't seem to have any problems with this short burst - but just
> wondering if this short duration high swr could do damage? by the way how
> high
> an swr is acceptable - just wondering? thx, john
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