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From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <524864BC.60908@iup.uni-heidelberg.de> <6C620201432A459BBD435B0ADFA16DD3@gnat> <524870EB.3090708@iup.uni-heidelberg.de>
Date: Sun, 29 Sep 2013 21:36:36 +0100
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Subject: Re: LF: Re: HF SWR meters on MF?
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Status: O

No it does not.....BUT I did not imply that, with knowledge, it can not=20
yield useful information....Too many think 1:1 swr means resonance. A fri=
end=20
of mine used to do a demo at clubs where he had a closed box with coax go=
ing=20
into it and a reading 1:1 on a meter. He asked what was in the box and th=
e=20
guess was usually a dummy load. He then in true stage magician style got=20
someone to come and open the box and display what he found. To their=20
amazement there was only several metres more coax left open at the end !!=
 Of=20
course the frequency setting of the exciter was vital :-))

Having detuned your antenna you could bring the non-resonant result to 1:=
1=20
by then changing the tranformer ratio....But that would not indicate=20
resonance.:-))

When I got into radio 60 yeas ag the Club sages of the time stressed firs=
t=20
resonate, then match. That was before many SWR meters were around though =
the=20
"Monimatch" had been described in QST few understood how it worked, or ho=
w=20
to use it. Most resonated with a GDO and matched for max antenna current

Actually for your purpose I would suggest you look at the tuning aid=20
described by Jim Moritz M0BMU in a number of the books (LF Today)  and=20
probably on several web sites. It was original designed in the 136kHz day=
s=20
but should be just as useful at 470k. This aids the tuning and matching=20
process.

A lot of topband meters should work try them with a load, then two loads=20
"teed" together, also use different length of coax between the load and=20
meter.....it should give sensible results.

Alan

----- Original Message -----=20
From: "Stefan Sch=E4fer" <Stefan.Schaefer@iup.uni-heidelberg.de>
To: <rsgb_lf_group@blacksheep.org>
Sent: Sunday, September 29, 2013 7:26 PM
Subject: Re: LF: Re: HF SWR meters on MF?


Does it not?
I suggest to do a test:   Use a MF antenna (on 160m, for this test),
resonate it to the TX frequency by using a variometer. Then use a
ferrite transformer to match the impedance to 50 Ohm.

Insert the SWR meter (i'm using this one for HF:
http://www.astrosurf.com/luxorion/Radio/swr-meter.jpg   (you can find
the words "SWR" and "meter" on the instrument) into the signal path.

I bet it will show something close to 1:1. The detune the variometer
(i.e. add a significant reactive component to the feed point impedance)
so that the resonance is lost. I bet that the reflected power will rise
dramatically. Then i interprete that the SWR meter tells me that i have
lost the resonance, since the ratio of the transformer didn't change.
Sure, there could be a change of the earth losses which cause a change
of the resistive component of the impedance. This will result in a
change of the SWR as well. But these changes are small compared to the
possible change of the reactive part, especially on MF and LF...

73, Stefan


Am 29.09.2013 20:02, schrieb Alan Melia:
> er ......an SWR "meter" will tell you nothing about resonance :-))
> Alan
> G3NYK
>
> ----- Original Message ----- From: "Stefan Sch=E4fer"=20
> <Stefan.Schaefer@iup.uni-heidelberg.de>
> To: <rsgb_lf_group@blacksheep.org>
> Sent: Sunday, September 29, 2013 6:34 PM
> Subject: LF: HF SWR meters on MF?
>
>
>> Hi MF,
>>
>> Did someone try to use a normal HF SWR meter on 630m? They are=20
>> specificated down to 1800 kHz of course but what about 472 kHz?
>>
>> At least it would be good to get some indication that:
>>
>> -There is some output power (e.g. when using an IC706)
>> -One is coming closer to resonance
>> -Impedance is/comes close to 50 Ohm
>>
>> I'm supporting a new potential MF RX station with limited equipment (n=
o=20
>> oscilloscope...)...
>>
>>
>> 73, Stefan/DK7FC
>>
>
>