[Moon-net] RG405 and 25ohm cable

[Eddy GORA]

Thanks a lot for so quick reply, I got this cable sometime ago from Farnell
available in YO and now have abt. 2m for coupling purposes. In app. notes by
Philips there are a lot of unusual coax. like 35 ohm or even strange 10 ohm
?! never heard of this type, where did they got those cables I really don't
know...
Will use on in/out baluns 144MHz only and just for 2xBLF278 ~ 4-500W.

Edi, YO3HCV 

-----Original Message-----
From: Chris Bartram [mailto:chris at chris-bartram.co.uk] 
Sent: Tuesday, July 10, 2007 3:12 AM
To: Eddy GORA
Subject: RG405 and 25ohm cable

Hello Eddy

>Anyone know where I can get (cheap) some 25 Ohm semi rigid coax ? I 
>have a Ericsson BLF278 power unit from some pager sys. around 172 MHz 
>need to transform for 2m. I also look for 50 Ohm semi rigid, 5mm or 
>larger because I already have RG-405 brand-new but need more power 
>resistant. One last
>(dummy) question : if joint in parallel 2 pieces on RG-405 can I insert 
>double power than specified from cable ?

For a one-off amateur system, I wouldn't bother trying to find 25ohm cable. 
Parallelled 50ohm cable will work as well.

The power rating of parallelled 50ohm cables is going to be ~1.4 times the
rating for a single cable: you'll double the current rating, but the voltage
breakdown won't increase. 

In amateur service RG405 will handle 1kW at 432 if the cable is reasonably
matched. I've used it in baluns carrying 250W with a very small temperature
rise. In practice, RG405 tends to be limited by current handling: look at
the voltage breakdown characteristics of teflon!

Vy 73

Chris
GW4DGU

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