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PF1F > TECH 28.01.05 22:51l 60 Lines 2062 Bytes #999 (0) @ WW
BID : CA0067PF1F
Read: GUEST OE7FMI
Subj: Re: Coupler for 2 Tx into 1 ant?
Path: DB0FHN<DB0THA<DB0ERF<DB0FBB<DB0BI<DB0NOS<DB0EA<DB0ACC<DB0GOS<DB0PKE<
PI8DAZ<PI8WFL
Sent: 050128/2038Z @:PI8WFL.#NH1.NLD.EU #:16489 [Enkhuizen] $:CA0067PF1F
From: PF1F@PI8WFL.#NH1.NLD.EU
To : TECH@WW
G8MNY wrote:-
> I computer modelled the normal low loss RF TV combiner & I
> was disgusted at the results.
>
> SOURCE 1 ÄÄÂÄÄÄÄ¿ 1:1
> 75ê ³ |)
> 300ê |)ÄÄÄ COMBINED 75ê
> ³ |) LOAD
> SOURCE 2 ÄÄÁÄÄÄÄÙ
> 75ê
>
> Although this nulled OK as signals from SOURCE 1 were cancelled
> at SOURCE 2 the impedance seen by source 1 was 150ê & the O/P was
> 6dB down on the SOURCE 1 port level, although this would be less in
> practice as the level will jump up with less load.
>
> So I have come up with a theoretical 2 ferrite transformer design,
> that may be practical. And with suitable trimmer Cs I expect I can
> get a good mix product null on a spectrum analyser.
>
> Cross over
> TX1 ÄÄÄÂÄÄÄÄ¿ ÚÄÄÄÄÂÄÄÄÄ TX2
> 50ê ³ X ³ 50ê
> ³ ÚÄÄÙ ÀÄÄ¿ ³
> )|( )|(
> 1:1 )|( )|( 1:1
> )|(_______)|(
> ³ ³ ³
> ³ 50ê ³
> ³ AERIAL ³
> ÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄ
>
> There are coax designs that may be better, I wait for replies on designs.
I don't know though, seems that all the power from TX1 goes into TX2, none
into the aerial. Same for TX2, it all goes to TX1. The aerial always gets
a null.
As far as I know, there is always a 6dB penalty if you want a (matched)
broadband coupler with no interaction between the input ports. It is sort
of a law of nature.
We coupled a few pairs of platform-service transmitters to one antenna per
pair using couplers like that on the local aerodrome.
If you can tolerate filters selective enough to tell the frequencies
apart, of course that would be different.
The first design is not really bad at all, provided you match the inputs,
or make it half the impedance it is now, and match the output.
Oh and if the frequency and phase are exactly the same, there is no loss.
An example would be a PA with two branches working in parallel, the
outputs coupled together (see: Wilkinson power combiner or splitter).
Rudolf, PF1F
Heemskerk, JO22im
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