| |
VK2ZRG > TECH 26.01.05 10:32l 63 Lines 2447 Bytes #999 (0) @ WW
BID : 1077_VK2ZRG
Read: GUEST OE7FMI
Subj: Re Coupler for 2 Tx into 1 ant?
Path: DB0FHN<DB0FOR<DB0SIF<DB0EA<DB0RES<DK0WUE<7M3TJZ<HG8LXL<I0TVL<VK2BNR<
VK2TGB<VK2IO<VK2AAB
Sent: 050126/0551Z @:VK2AAB.SYD.NSW.AUS.OC #:40012 [SYDNEY] FBB7 $:1077_VK2ZRG
From: VK2ZRG@VK2AAB.SYD.NSW.AUS.OC
To : TECH@WW
VK2ZRG/TPK 1.83d Msg #:1077 Date:26-01-05 Time:5:41Z
Hello technical bods,
Re: Coupler for 2 Tx into 1 ant? (Query from G8MNY to TECH@WW)
The answer is simple John, Just use a 3 dB rat race hybrid made from 70.7 ohm
coax cable. I made a simple computer model using PUFF and find it gives perfect
isolation between the two input ports and a 3 db loss between either input port
and the common output port. With a 50 ohm load, the return loss into the input
ports is > 60 dB when 70.7 ohm coax is used for the construction, and > 25 dB
if you use 75 ohm coax. These figures assume that you have a perfectly matched
50 ohm termination on the forth port. Bandwidth is around 10 percent.
The termination absorbs half the input power from either input port when the
two inputs are not phase coherent. If the inputs are in phase then no power
goes into the termination, the two input signals add at the output port.
The only limitation on input power is heating in the coax cable and the power
rating of the 50 ohm termination.
A variation on the 3 dB rat race hybrid is to use a Wilkinson
splitter/combiner. This design needs just two 90 degree lengths of 70.7 ohm
coax and the `termination' is a 100 ohm balanced load between the input ports.
Wilkinson combiners/splitters can also be made from lumped elements.
See page 7-41 of the ARRL UHF/Microwave Experimenters Manual.
I've made Wilkinson dividers for the 70 cm band with strip lines on a PC
board and was able to get over 30 dB isolation without any trouble.
73s from Ralph VK2ZRG@VK2WI.#SYD.NSW.AUS.OC
/ack
Taglines Version 1.00, by Colin Coker G4FCN
C Program run, C Program Crash...ReWrite in Pascal!
>R:050124/1857Z @:GB7CIP.#32.GBR.EU #:30049 [Caterham] $:30049_GB7CIP
>
>From: G8MNY@GB7CIP.#32.GBR.EU
>To : TECH@WW
>
>Hi & thanks for reading. I am looking for a design for coupling 2 low power VHF
>Tx (1W band1 for 2 SAB mono links) close in frequency into 1 aerial. There are
>no Rx involved at the Tx sites so absolute nulling is not required, but the
>problem is that each Tx must not see any significant power from the other Tx as
>PA mixing will occur giving normal mix products.
>
>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
Read previous mail | Read next mail
| |
