And some of the demos when done at CB clubs in the early days of UK
27Mhz licensing used to frighten the audience when they saw just what
"sacrileges" would be committed with "expensive" chicken boxes and "bits
of wire"!
Of course, they were always advised "Don't try this at home - unless
under the supervision of a responsible adult!"
My favourite will always remain the manufacturers agent who came into
our store and attempted to get us to stock "SWAR GREASE" - apparently
you could ignore "SWAR" meters, the grease would guarantee a perfect match!
73
On 29/09/13 21:36, Alan Melia wrote:
No it does not.....BUT I did not imply that, with knowledge, it can
not yield useful information....Too many think 1:1 swr means
resonance. A friend of mine used to do a demo at clubs where he had a
closed box with coax going into it and a reading 1:1 on a meter. He
asked what was in the box and the guess was usually a dummy load. He
then in true stage magician style got someone to come and open the box
and display what he found. To their amazement there was only several
metres more coax left open at the end !! Of course the frequency
setting of the exciter was vital :-))
Having detuned your antenna you could bring the non-resonant result to
1:1 by then changing the tranformer ratio....But that would not
indicate resonance.:-))
When I got into radio 60 yeas ag the Club sages of the time stressed
first resonate, then match. That was before many SWR meters were
around though the "Monimatch" had been described in QST few understood
how it worked, or how 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
described by Jim Moritz M0BMU in a number of the books (LF Today) and
probably on several web sites. It was original designed in the 136kHz
days but should be just as useful at 470k. This aids the tuning and
matching process.
A lot of topband meters should work try them with a load, then two
loads "teed" together, also use different length of coax between the
load and meter.....it should give sensible results.
Alan
----- Original Message ----- From: "Stefan Schäfer"
<[email protected]>
To: <[email protected]>
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 Schäfer"
<[email protected]>
To: <[email protected]>
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
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
(no oscilloscope...)...
73, Stefan/DK7FC
--
73 de pat g4gvw
es gd dx
qth nr Felixstowe
East Coast UK
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