[Moon-net] Information req'd on use of copper pipe

[Chris Bartram]

Hello Charlie

> I am trying to get my station setup on 10m GHz EME completed and as opposed
> to running the TWT remoted behind the dish I had the thought of using some
> copper pipe as W/G .  This would simplify my system and allow me to get QRV
> sooner rather than later.

You'd be very welcome on the band...

> I have a few questions for anyone that can help:

> 1.  Is it feasible / possible to use 1/2 inch or 3/4 inch round copper tube
> as a W/G on 10 Ghz? 2.  If so is there any information on making 
> transitions to  WR 75  or 90   and to coaxial from round copper pipe? 3. 
> What losses can I expect with copper pipe?

In theory, circular waveguide will work, but it is more difficult to do than 
it seems on surface. The problem is that it doesn't require a big 
discontinuity, in terms of a slightly irregular cross-section, to change the 
polarisation. In practice this means that any bends or curves will cause 
problems, even if you launch CP into the guide.

> 4.  I plan to run CP on 10 GHz so I suspect the depolarization that would
> occur in the copper pipe is not an issue.Is this correct?

Unless you have perfectly straight and uniform pipe, no! See above.

There's a general movement to move towards CP in Europe, and although there's 
a certain amount of 'who's going to jump first' involved, I think that many 
of us are working on it! 

I currently use a 35W TWT mounted at the feedpoint of my little 2.4m dish. The 
system is still linearly (local vertical) polarised, and I use coaxial 
changeover switching. I'm working on a new system which will allow me to run 
both CP and linear pol. and will integrate a 150W TWTA with waveguide 
switching. To do this I'm planning to use a 12m length of Andrews elliptical 
semi-flexible WG, rather than run the DC feed to the TWT. My problem is 
finding time due to work!

I'm happy with the 4kV helix supply associated with the current tube going out 
to the dish via a DC feed umbilical, but the idea of 10kV at rather higher 
current floating about in the damp atmosphere of west Wales starts to get 
scary!

> I have my CP  feed  and LNA assembly completed and I only need to get power
> from the TWT to the feed before I can be QRV.

It might be worth looking for a length of elliptical guide - certainly over 
here the guys in the TV transmission business seem to be able to get hold of 
used lengths, as systems are upgraded. The main problem is keeping the stuff 
out of the scrapyards, where they strip-off the outer jacket and sell-on the 
WG as copper scrap.

Vy 73

Chris
GW4DGU