Message-ID: <57405F26C6A94F04B25E124CC1F9814B@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> <9E19F2EA072B4AE3A7A112534A29B460@gnat> <323462263.20151015234436@chriswilson.tv>
Date: Fri, 16 Oct 2015 00:45:49 +0100
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Subject: LF: Re: Should I be aiming for a better match than this?
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Status: O

Hi Chris Im glad the tap idea helped. It is quite difficult at a distance to 
think of things that might cause the effects but it looks like we nailed 
one.

Your suggestion of RF getting into the system is a good one. It is always 
difficult with a short antenna because you have a lot of radiation near the 
equipment.When I started using a 130ft end fed wire on HF with an FT-101 and 
its low-Z dynamic mic I got terrible problems not seen when I used a 
Heathkit HW100 with a crystal mic. The latter was a lot easier to by-pass 
for RF. Eventually a trial with a ferrite rod (ex MW aerial ferrite) pushed 
into the coils of the curly lead completely stopped the problem. I had no 
trouble on CW....only when the mic was in.

What you need to find is where the RF is affecting, then how its getting in. 
It may well be that some of the chassis' is going live to RF ....if that is 
the case you may even feel it :-((

Try to make sure that the RF stays outside the shack if you can. Ground the 
antenna end of the coax......try to run the coax at right angles to the 
aerial as it leaves the coil. Possibly put some beads on the the remote end 
of the coax or a couple of turns through a torroid. I think you have a 
ferrite coupled current meter?? put it over the coax when you are using the 
dummy load. You shoud see very little current indicated, do the same with 
the aerial/tuner connected and I guess you will see a lot more. That (if it 
is the case) will give you something to aim at. Get the readings  similar to 
those on the dummy load. I think the RF is probably comming back on the coax 
braid.

That's my best guess at the moment.....my, you are learning a lot of 
practical radio in a short time :-))  I may be totally off target but it a 
good place to start.

Best of Luck
Alan
G3NYK


----- Original Message ----- 
From: "Chris Wilson" <chris@chriswilson.tv>
To: "Alan Melia" <rsgb_lf_group@blacksheep.org>
Sent: Thursday, October 15, 2015 11:44 PM
Subject: Re[2]: LF: Re: Should I be aiming for a better match than this?


> Hello Alan,
>
> Wednesday, October 14, 2015
>
>
> Hi again Alan. Thanks for the info. I have got a better match by
> making a new tap on the loading coil between 2 existing ones and now
> the variometer will shift the phase side to side as expected. You were
> spot on there!
>
> Today I have finally got what I think is a handle on what's happening.
> If I TX into my dummy load, from lowest power to highest there is no
> odd waveform displayed. As one would expect the V and I are in perfect
> phase, and they look like a single trace.
>
> If I connect my aerial set up sometimes I can get a near perfect phase
> and amplitude, but after a while it starts to go awry, for no apparent
> reason. The voltage trace gets a dog leg in it, that gets worse.
> Sometimes I can actually alter the shape of the traces with the output
> level control on my TS-590 exciter. Similarly sometimes I can tweak
> things right again with the audio level from the sound card, in either
> WSPR or OPERA modes.
>
> However, when TX'ing into a dummy load the RF level from the TS-590
> exciter and the audio level have very little, if any, impact on the
> scopematch waveforms save when the level drops below about -10 dBm.
> Then of course drive is lost and the amp trips out.
>
> The circa 0 dBm maximum DRV out from the 590 goes to a pre amp inside
> the amplifier, then to a frequency doubler, then into the input side
> of the G3YXM amp circuitry.
>
> What I have discovered, and I am pretty sure this is what is
> happening, is that at higher power levels RF is getting back into the
> input of the amp, or the CMOS stuff or low volatage power supply, and
> it seems to sort of "run away with itself".
>
> I placed a BNC T at the input of the amp, where a short RG-58 co-ax
> cable feeds it from the DRV (exciter) output from the TS-590. A -10dBm
> to 0 dBm signal from the 590, say generated bu the TUNE function in
> WSPR is immediately modulated, even running low power, and at high
> power from the amp there's a lot of signal imposed. If I disconnect
> my antenna co-ax at the amp and run a long co-ax to my dummy load,
> there's no noticeable modulation of the input. Am I right in thinking
> that would mean there is no INTERNAL cross talk within the amp itself,
> or have I got that wrong?
>
> I would welcome tips as to how to test how the RF is getting in, and
> where, please. Another poster, John Rabson, talked of isolating mains
> ground and RF ground. As I have had occasional RCD trips at the house
> distribution panel when TX'ing at high power with this setup, I am
> wondering about this. He spoke of an isolation transformer, but I am
> not sure just what he meant by that. Apart from the normal house mains
> grounding of the amp case my only other ground is a six foot spike
> near the loading and matching coil, about 10 feet away and connected
> to the matching coil earthy end and the braid of my coa-ax feed from
> the  amp  to the matching coil. As my shack is upstairs I have not had
> much  luck using it as an RF ground as the cable length to it radiates
> on  HF,  so  I have tended not to use it at all, and with a horizontal
> loop  as  an  HF aerial I didn't need to feed it against ground like a
> ling wire for example.
>
>
>> 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
>
>
>
>
>
>
>
>
>
> -- 
> Best regards,
> Chris                            mailto:chris@chriswilson.tv
>
>