I would be curious to hear a more technical explanation of this. Surely,
there might be a different SWR reading from the exciter's perspective when
an additional component is switched in. With many tube-type amplifiers, the
exciter might see a nominal 50 ohm load because of a tuned cathode circuit
in the amplifier, even though the actual antenna may have a very high
standing wave. The resonance characteristics of the antenna which account
for standing waves, assuming the feed line to be matched or appropriate,
will not change, regardless of what component is connected to the coax, at
least in my opinion. I have run who knows how many linear amplifiers and
have built at least a half dozen of them, never having seen the SWR rise
above what I saw in my exciter, once the amp was tuned appropriately. 1 to 1
at the tranceiver, still 1 to 1 at linear output with pi out or other tuning
circuit adjusted properly. Correspondingly, if I see a SWR of 2.1 at the
exciter, there is absolutely no way I will truly reduce that SWR for the
linear other than creating the illusion of having done so by tuning out
reactance with an LC circuit.
I'm still learning after 50 years a ham so will be delighted to keep it up
if someone can give me a good rebuttal to my very possibly incorrect view of
things.
Jerry, v e 3 q s o
[log in to unmask]
----- Original Message -----
From: "Colin McDonald" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Sunday, February 20, 2005 4:02 AM
Subject: Re: Talking Watt Meter from LDG
> with the amp inline as opposed to out of line, the swr could vary because
> of
> the extra component between radio and antenna/antenna tuner. So to varify
> swr after the amplifier is actually physically connected in line you have
> to
> check after the amp and if you have a high powered amp that you wish to
> run
> at full rf output while checking things to insure stability then a meter
> that can handle the power is necesary...this is why naturally they rate
> meters for power like 2000 watts instead of only 2 or 300 that the radio
> could put out.
> With the coax hooked directly into the radio from a tuner or direct to an
> antenna the swr will likely be different then that when the amplifier is
> physically connected in line..that was the point of what i said or i guess
> why i refered to a higher power handling meter as something a little more
> useful, at least for anyone running 625W plus.
> It probably wouldn't change however if you just by-passed with a relay or
> stand by/off switch on the amplifier because then the extra component
> would
> still physically be there even though the unit is not being used..
> Regards
> Colin
> ----- Original Message -----
> From: "Jerry Neufeld" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Saturday, February 19, 2005 8:54 PM
> Subject: Re: Talking Watt Meter from LDG
>
>
>> Hello Colin and others.
>>
>> It's not altogether clear to me why one would need a SWR meter for power
> of
>> the kind generated by a linear amplifier. With the amplifier out of the
>> circuit, i.e., its relay in rest position, the exciter, unadjusted,
>> looked
>> into whatever standing wave characteristics an antenna has. Those
>> characteristics, from my perspective, do not change, whether or not one
>> tunes out inductance and reactance with LC adjustable circuits. In short,
> if
>> a 50 ohm antenna appears flat with ten watts forward, it will or should
>> remain flat with a full thousand. If wide-spaced variable capacitors are
>> used to tune out these things, as done in high power amps with tubes,
>> then
>> adjusting for maximum RF output is likely to be the optimal adjustment
>> capable with that amplifier. If my presumptions are true, why look for a
>> high power SWR meter, unless, of course, one wishes simply to look at
>> SWR,
>> once maximum RF out has been attained.
>>
>>
>>
>> Jerry, v e 3 q s o
>>
>> [log in to unmask]
>>
>> ----- Original Message -----
>> From: "Colin McDonald" <[log in to unmask]>
>> To: <[log in to unmask]>
>> Sent: Saturday, February 19, 2005 2:36 PM
>> Subject: Re: Talking Watt Meter from LDG
>>
>>
>> > nope, it only goes up to 54MHZ...but it will handle up to 2000 watts
> where
>> > as remy's meter only handles max 625 RMS.
>> > When you are tuning an antenna with an amp you certainly want to make
> sure
>> > the swr between the amp and antenna or antenna tuner is right not just
>> > between radio and amp.
>> > So for anyone who wants to use over 625watts then the ldg meter would
>> > be
>> > better.
>> > However, since they dont offer a vhf version of the meter you would
>> > also
>> > need remy's meter for that....also if you are real picky about
> resolution
>> > the ldg meter is accurate to 5 percent either way where as the other is
>> > ten
>> > to fifteen percent accuracy.
>> > Regards
>> > Colin
>>
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