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Date: Sun, 29 Sep 2013 23:29:25 +0100
From: pat <g4gvw@aol.com>
Organization: G4GVW
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Subject: Re: LF: Re: HF SWR meters on MF?
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Status: O

And some of the demos when done at CB clubs in the early days of UK=20
27Mhz licensing used to frighten the audience when they saw just what=20
"sacrileges" would be committed with "expensive" chicken boxes and "bits=20
of wire"!

Of course, they were always advised "Don't try this at home - unless=20
under the supervision of a responsible adult!"

My favourite will always remain the manufacturers agent who came into=20
our store and attempted to get us to stock "SWAR GREASE" - apparently=20
you could ignore "SWAR" meters, the grease would guarantee a perfect matc=
h!

73


On 29/09/13 21:36, Alan Melia wrote:
> No it does not.....BUT I did not imply that, with knowledge, it can=20
> not yield useful information....Too many think 1:1 swr means=20
> resonance. A friend of mine used to do a demo at clubs where he had a=20
> closed box with coax going into it and a reading 1:1 on a meter. He=20
> asked what was in the box and the guess was usually a dummy load. He=20
> then in true stage magician style got someone to come and open the box=20
> and display what he found. To their amazement there was only several=20
> metres more coax left open at the end !! Of course the frequency=20
> setting of the exciter was vital :-))
>
> Having detuned your antenna you could bring the non-resonant result to=20
> 1:1 by then changing the tranformer ratio....But that would not=20
> indicate resonance.:-))
>
> When I got into radio 60 yeas ag the Club sages of the time stressed=20
> first resonate, then match. That was before many SWR meters were=20
> around though the "Monimatch" had been described in QST few understood=20
> how it worked, or how to use it. Most resonated with a GDO and matched=20
> 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=20
> days but should be just as useful at 470k. This aids the tuning and=20
> matching process.
>
> A lot of topband meters should work try them with a load, then two=20
> loads "teed" together, also use different length of coax between the=20
> load and meter.....it should give sensible results.
>
> Alan
>
> ----- Original Message ----- From: "Stefan Sch=E4fer"=20
> <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=20
>>> (no oscilloscope...)...
>>>
>>>
>>> 73, Stefan/DK7FC
>>>
>>
>>
>
>


--=20
73 de pat g4gvw
es gd dx
qth nr Felixstowe
East Coast UK