Message-ID: <9E19F2EA072B4AE3A7A112534A29B460@gnat>
From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <1541636554.20151013163425@chriswilson.tv> <43464DACBFAA49C08A73FB93FFF52105@gnat> <603371935.20151014123307@chriswilson.tv>
Date: Wed, 14 Oct 2015 15:06:40 +0100
MIME-Version: 1.0
Subject: Re: LF: Re: Should I be aiming for a better match than this?
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Status: O

Hi Chris well it may depend where abouts in its rotation the movable coil 
is. If you think of tuning a coil with a ferrite slug you can get a peak 
when the core is in the middle of the coil. However to get it right you need 
two peaks, one with the core at the top of the coil and one where it is at 
the bottom and a dip in the middle.  Now its different with the variometer I 
know because you have the phase indication which should indicate too 
much/not enough reactance. I am thinking if you have say too much 
inductance, as you rotate the varible coil the antenna will come closer to 
resonance then as the turning continues it will go away again. However I 
would expect the phase shown on the scope to stay the same side showing say 
always below resonance. (then you would tap up a bit from the bottom and try 
again). The current and voltage traces should sweep past each other but not 
jump one side to other. That is rather odd.

I'm sure you can find a few 3m dishes if you really want to look like GCHQ 
:-))  Of course the higher you put your antenas the less obvious the are and 
the smaller they look
 :-))

Alan
G3NYK
----- Original Message ----- 
From: "Chris Wilson" <chris@chriswilson.tv>
To: "Alan Melia" <rsgb_lf_group@blacksheep.org>
Sent: Wednesday, October 14, 2015 12:33 PM
Subject: Re: LF: Re: Should I be aiming for a better match than this?


> Hello Alan,
>
> Tuesday, October 13, 2015
>
>
>>>>can i work out the antenna current from this?
>> Not really this is the current in the coax. If the current and voltage 
>> are
>> not in phase then by definition you have reactance in the coax 
>> termination.
>> You should try adjusting the variometer for current and voltage in phase
>> (that is resonance) , then adjust the turns ratio on the transformer to
>> match the resultant aerial resistive component to the 50ohm coax (if
>> possible :-))  ) That should give you optimum performance.
>
>> The reactive load may be what is tripping the protection it will give 
>> bigger
>> voltages(or currents) than the matched condition.
>
>> Whilst you have been getting a signal out, I suggest the next experiment 
>> is
>> to try and reducethe ground loss before you spend a lot of time getting a
>> perfect match to an imperfect aerial system (only to have to do it all 
>> again
>> when you manage to get the ground loss down.)
>
>> Alan
>> G3NYK
>
> Thanks  Alan, appreciated as always. I may be doing something wrong as
> I  can't  seem to get the phase right, I will try later when my pal is
> free  again.  When he  turning the variometer coil either way even by
> tiny  amounts  the  phasing  seems to go either side of matched, but I
> couldn't  see  a perfect match on the scope, which seems rather odd. I
> intend  to try reducing ground losses, but it must be done discreetly,
> the  wife  gets worried when she sees me carrying large coils of wire
> into  "her"  garden ;) She talks of the place looking like GCHQ... Now
> what's wrong with that? ;)
>
>
>
>
>
>
> -- 
> Best regards,
> Chris                            mailto:chris@chriswilson.tv
>
>