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Tandembridge für Pure Signal verwenden?

Verfasst: Sa Okt 13, 2018 8:32 pm
von DH1KLM
Hallo,

ich habe aus einem SWR / Power Meter Projekt einen Tandembridge liegen. Aufgebaut wie auf Seite 10 beschrieben.
IMG_20181013_201946.jpg
Könnte ich den FWD Anschluss für Pure Signal verwenden?

Re: Tandembridge für Pure Signal verwenden?

Verfasst: So Okt 14, 2018 10:12 am
von f6itu
Hi

Just a stupid question : what is the impedance on the sma fwd connector when something is plugged on it ?

the input Z of the AD8307 is 50 Ohms. The output network of Loftür's coupler is 50 Ohms also
https://3f7d437a-a-62cb3a1a-s-sites.goo ... edirects=0
the output of the fwd sma (ps out) is 50 Ohms again

so what is the impedance of 3 x50 Ohms loads connected together ? certainly not 50 Ohms. Unless you disconnect the AD8307 input circuit, you should add a 6 db splitter inside your coupler. (3x16 Ohm resistors in "Y" configuration, or a 3x50 Ohms splitter in "delta" configuration )

https://www.radio-electronics.com/info/ ... ivider.php

another solution would be to keep preciously your coupler aside, and add a capacitive or resistive pad.
https://www.webx.dk/oz2cpu/radios/miliwatt.htm
chapter "How To Measure High Power"

A capacitive pad only needs 2 high voltage capacitor

To give you a more precise idea, you can have a look on the last version of W6PQL's coupler with it's "pure signal" sampling output
https://www.w6pql.com/hf/hfddd-assembly3.htm
The 6 dB splitter is located in the forward branch.

You always can connect PS on your sma FWD output without precaution. But your power reading will be wrong and the insertion losses of your coupler will go up. The tandem match configuration is easy to build, but if you don't care, it's bandwidth will be narrowed and it's VSWR will increase (which is not really logic for a device used to measure VSWR)

73'
Marc f6itu

Re: Tandembridge für Pure Signal verwenden?

Verfasst: So Okt 21, 2018 12:00 pm
von DH1KLM
Danke an Ernst und Marc für die Antworten,
Ich bin mir nicht sicher, ob ich die Idee mit dem Tandemkoppler weiter verfolgen werde, da ich ohnehin die PCB's
von wiki.electrolab.fr habe und beabsichtige, ein paar davon in der dunklen Jahreszeit zu bestücken.