Date: Fri, 16 Oct 2015 15:48:54 +0100
From: Chris Wilson <chris@chriswilson.tv>
Organization: Gatesgarth Developments
Message-ID: <265609317.20151016154854@chriswilson.tv>
To: Graham <rsgb_lf_group@blacksheep.org>
In-Reply-To: <10FBC32E57324835BDD4008B3133BC11@AGB>
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Subject: Re[2]: LF: Re: Should I be aiming for a better match than this?
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Status: O

Hello Graham,

Friday, October 16, 2015


> 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..


I have found the Zobel network resistor (22 Ohms, 25W) badly
overheated but not open. I also found one leg of one of the 4n7 caps
on the primary of T1 the output transformer broken. I don't have
another metal clad panel mount of the right resistance unless I
parallel two 47 Ohm 50 Watt ones, but there's not enough physical
space, so I have put the old one back until a new one arrives, and
renewed the 2kV 4n7 cap. I now see roughly square waves from both
sides of the output, looking before the filter network. Before I had
only one squarish wave and a funny wiggle showing on the scope.


I would like to know if the broken leg on this cap could have caused
the Zobel wirewound to overheat though. As I noticed the odour days
ago. Sadly my inexperience has made me build the thing with scant
reagrd to access for repairs or even to look for smoke. If I did it
again I would spread stuff about more in a single layer!

The meter still doesn't seem to read as high FWD, as it did, and shows
some reflected power, but it seems to be getting out OK again. As I am
learning a lot as I go it's no big deal. If it just worked I wouldn't
have learnt half as much about HOW it works as I do now :) It's TX'ing
OPERA 32 on 136 kHzas I type. Maybe now the output stage is correct
again the loading needs tweaking a bit. Scopematch looks OK though.

Thanks for the reply Graham.


-- 
Best regards,
 Chris                            mailto:chris@chriswilson.tv