Dave
If you're into Big Bad Amps...
Don't put those kind of thoughts in my head ;-)
I think with Steve's antenna setup and 1KW we are very close to 1W ERP. The
Wilkinson seems to work great... Ran it full out last night for a couple of
hours into the dummy load... I couldn't measure the loss from the combiner
as it is very low and the system remains >80% eff.
73 Scott
----- Original Message -----
From: "Dave G3WCB" <[email protected]>
To: <[email protected]>
Sent: Tuesday, March 01, 2005 3:13 AM
Subject: LF: Big Bad Amps <was re: ... --- ...>
Hi, Scott.
, you should check out G4FTC's site
http://www.qsl.net/g4ftc/amplifiers/136khz/home.htm He describes a 3kW LF
amp. that uses 8 x IRFP450's in a bridge arrangement. Biggest PA I've seen
so far!
BTW, if you have two identical TX's already, and you find the Wilkinson
thing doesn't work out, you could re-configure your amps. into a bridge
arrangement instead, bit like the Decca TX's.
Keep that fire-blanket handy!
Cheers,
Dave G3WCB.
-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Scott Tilley
Sent: 01 March 2005 10:59
To: [email protected]
Subject: LF: Re: Re: ... --- ...
Hey Alan
We got the bugs out... Once I found the problem with the lack of sinc in
the 4013 divider stages things have been working as expected. I thought
about the inductor coupling; however, based on my observations the
combiner
is not doing anything negative to the signal train. We still have >80%
eff.
I would like to try this with toroids next and compact it down. I'm also
dreaming up a bigger badder amp using this concept. It seems real stable
and doesn't require running the system 'balls to the wall' to get some
serious power from 4 FET and a reasonable PSU voltage.
73 Scott
----- Original Message -----
From: "Alan Melia" <[email protected]>
To: <[email protected]>
Sent: Tuesday, March 01, 2005 2:49 AM
Subject: LF: Re: ... --- ...
> Hi Steve I have just had a thought your construction looks fine....BUT
maybe
> the two coils are too close together and there is some coupling. I
wonder
if
> it is possible to temporarily turn one at right angles to kill any
coupling
> and see if that helps??
> The biggies in my Web page were made with big toroids I believe probably
> iron dust rather than ferrite, as the inductance reqquired is not that
high
>
> Cheers de Alan G3NYK
>
> ----- Original Message -----
> From: "Scott Tilley" <[email protected]>
> To: <[email protected]>; <[email protected]>
> Sent: 01 March 2005 06:51
> Subject: LF: ... --- ...
>
>
> The smoke test of this Wilkinson Combiner was successfull in that no
smoke
> came out and nothing died. However, we get enough heat to cook an egg
on
> the 100ohm balance resistor.
>
> We have a scope match on the output to the dummy load and it shows about
> 225W from one transmitter, add another and we get 450W, success NOPE!
The
> transmitters are outputting ~450W each! Therefore, half the power is
being
> absorbed in the 100ohm balance resistor. Examining the phase
relationship
> of the input to the combiner waveforms indicates they are in phase
within
> ~10degrees and almost equal in amplitude. So what gives! Anyone have
some
> idea what may be going wrong? Of course we have checked and doubled
checked
> the circuit for errors and nothing... All seems as it should according
to
> formulas and drawings we have viewed and designed it from.
>
> Does anyone have an idea how we could troubleshoot our way through this?
>
> Any advice would be appreciated.
>
> 73 Scott and Steve(It's all his fault ;-)
>
>
> Check the status of radio beacon 'TIL' in CN89lg at:
> www.scottboxx.com/radio
>
>
>
>
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