Message-ID: <10FBC32E57324835BDD4008B3133BC11@AGB>
From: "Graham" <g8fzk@g8fzk.fsnet.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <1541636554.20151013163425@chriswilson.tv> <43464DACBFAA49C08A73FB93FFF52105@gnat> <603371935.20151014123307@chriswilson.tv> <9E19F2EA072B4AE3A7A112534A29B460@gnat> <323462263.20151015234436@chriswilson.tv> <57405F26C6A94F04B25E124CC1F9814B@gnat> <867200100.20151016094832@chriswilson.tv>
In-Reply-To: <867200100.20151016094832@chriswilson.tv>
Date: Fri, 16 Oct 2015 15:20:14 +0100
MIME-Version: 1.0
Importance: Normal
Subject: Re: LF: Re: Should I be aiming for a better match than this?
Content-Type: text/plain;
	format=flowed;
	charset="iso-8859-1";
	reply-type=original
Content-Transfer-Encoding: 8bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Status: O

I am wondering if this feedback or whatever sometimes happens has
damaged a FET, can one or more of the 4 fail and still leave it
operational, but with reduced power and more reflected power?

Sorry to read that  Chris ,

 I often  thought  wspr  would  of  been  better  named  'ICARUS' , you 
where  +10 dB  and more in hand on your  OP32  spots , I did  see  G3XKR 
showing  -4 dB  on  the  first  day , but only the  one time, later spots 
where  lower ,  [the  s/n is  the  average  over the  tx cycle and  quite 
accurate],

Could problems  of struck  after this ?

The  reflected power, is  most likely  to be  the  return of  harmonic 
energy from the  ATU, caused by  waveform distortion, your class e/d amp is 
based on producing  a  pulse train,  fo is recovered by the  filter / ATU ,

One of the  Ł5 usb dongles in ds with  sharp-sdr  , will  give  you a 
usable  spectrum  plot of the  relative  levels , f0,f1,f2 f3  etc

73-Graham..

--------------------------------------------------
From: "Chris Wilson" <chris@chriswilson.tv>
Sent: Friday, October 16, 2015 9:48 AM
To: "Alan Melia" <rsgb_lf_group@blacksheep.org>
Subject: Re: LF: Re: Should I be aiming for a better match than this?

> Hello Alan,
>
> Friday, October 16, 2015
>
>
> Things took a sorry turn late last night, when making a final TX I
> noticed the meter in the G3YXM amp that switches between FWD / REF and
> measuring DC volts was reading low. Waveform voltages from the
> Scopematch looked much as always, but when changing the switch between
> forward and reflected power the forward power was perhaps less than a
> third on full power, and the reflected power was the converse and up a
> lot. I tried into the dummy load, which uses a different co-ax and it
> was the same. It was still putting a signal out into Germany, although
> the WSPR reporter networks seemed to show a big drop in received
> signal level.
>
>
> I am wondering if this feedback or whatever sometimes happens has
> damaged a FET, can one or more of the 4 fail and still leave it
> operational, but with reduced power and more reflected power? The
> failure I had with the output stage in the early stages of working
> with this was spectacular, noisy, smoky and terminal, leaving no
> output at all. For convenience the circuit is at:
>
> http://www.chriswilson.tv/amp.doc
>
>
> With regard to your advice below, I don't have a clamp on current
> meter, but did pick up a suitable little meter movement at the Newbury
> Rally to build one, so I will get one knocked together. I am
> suspecting my toroidal auto transforming matching transformer, it
> seems to need a bizarre feed tap, just one turn from the earthy end,
> and get pretty warm. I may build a galvanically isolated one like John
> Rabson has suggested. But first I need to find out what mischief I
> have done to the amp!
>
> I have now experienced the transmissions tripping the main house
> distribution RCD several times, and have realised that the recent
> random going off of the workshop alarm (panel shows a window knock
> sensor has set it off, but I am sure it's RF) coincides with
> transmission when the signal shows odd on the Scopematch. Thanks Alan.
>
>
>> 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
>
>
>
>
>
>
>
>
>
>
> -- 
> Best regards,
> Chris                            mailto:chris@chriswilson.tv
>
>