I've treated myself to a very nice BNIB 60cms Andrews dish from a 24GHz P2P system. It has a rear mounted ODU from which I have removed the feed arrangement, its two arms tuned to the separate RX and TX (23.448GHz) frequencies.
I want to use the Andrews circular dish insert with my 24GHz transverter which currently uses a SMA to WG launcher into a smaller 30cm dish.
Ideally I'd like to retain the WG clamping system on the andrews and have some spare WG with a flange on one end that I can then mount my SMA launcher on.

How should I 'terminate' what will be an open end of WG once I get past the recess in the round dish feed. (The white material seems to be some sort of foam to block insect ingress). The dish itself has its own cassegrain feed and a very nice spec. - +40dBi.
The 'crossover' hole in the original just looks like a milled slot. Can I literally just blank off the very end of my new WG feed, but with a crossover slot cut underneath to 'let the 24GHz out'??

Hope that makes sense...I'm sure the picture will!

Thanks

Gareth

Be smart if I actually attached the picture...
I'm also wondering what determines the polarisation of the signal?
Gareth

Gareth

Hi Gareth

Unless there is a sneaky twist inside the feed mechanism, I suspect you will get horizontal polarisation if the opening is at the top or bottom

 It looks as if the broad face of the entry waveguide is parallel to the feed assembly tube and almost certainly goes through an H plane 90 deg bend inside, you may be able to see the start of the bend  but the photo does not show it well

The WG entry looks  a little non standard dimensions but my guess is that if you offer up a squared off cut waveguide to it at 90 deg to how the original duplexing filter was fitted (assuming it is made from WG20), it will cover the gap and the mismatch will be acceptable You could fabricate a brass flange that would solder to the new guide a little behind the cut end which would allow you to mount you guide to the 4 threaded holes

I've treated myself to a very nice BNIB 60cms Andrews dish from a 24GHz P2P system. It has a rear mounted ODU from which I have removed the feed arrangement, its two arms tuned to the separate RX and TX (23.448GHz) frequencies.
I want to use the Andrews circular dish insert with my 24GHz transverter which currently uses a SMA to WG launcher into a smaller 30cm dish.
Ideally I'd like to retain the WG clamping system on the andrews and have some spare WG with a flange on one end that I can then mount my SMA launcher on.

How should I 'terminate' what will be an open end of WG once I get past the recess in the round dish feed. (The white material seems to be some sort of foam to block insect ingress). The dish itself has its own cassegrain feed and a very nice spec. - +40dBi.
The 'crossover' hole in the original just looks like a milled slot. Can I literally just blank off the very end of my new WG feed, but with a crossover slot cut underneath to 'let the 24GHz out'??

Hope that makes sense...I'm sure the picture will!

Thanks

Gareth

-- 
Mark  GM4ISM
gm4ism@...
dc2light.co.uk

Looks like a simple starpoint to me..

In a starpoint diplexer, the split is nominally lossless at each  of the Rx and Rx frequencies

The stopband of each filter provides a near perfect reflection (of predictable phase)

this 'rotates' down the waveguide  until it meets the common point where is produces an effective  short cct across the branch unused by the wanted frequency. thus the FR can only go one way (at that frequency)

Star point combining is common in coaxial systems.  It relies on a reasonable frequency separation between the 2 ports, as the filter has to have good rejection at the adjacent frequency

Mark GM4ISM

Hi Gareth

 

From the look of it ‘ it appears to be a form of magic T giving an equal split from the areal to each of the horizontal wave guides that I assume have tuning screws for the filters of the original TX and RX frequencies

So if you use the original configuration this being the easiest solution by retuning one of the filters or removing a filter you will be down by approximately 3 db   

I have retuned a number of these but only able to tune one of the filters onto 24 Ghz Amateur band

Paul

 

From: UKMicrowaves@groups.io [mailto:UKMicrowaves@groups.io] On Behalf Of Gareth G4XAT via groups.io
Sent: 15 May 2022 13:55
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] WG to circular

 

Be smart if I actually attached the picture...
I'm also wondering what determines the polarisation of the signal?
Gareth

--
Paul Bicknell G8KFW   South Coast UK

-- 
Mark  GM4ISM
gm4ism@...
dc2light.co.uk

Thanks for the explanations & suggestions...better photos attached.
The bore of the dish fitting is circular, this goes back nearly to the end of the coupling slot which has a flat-bottomed 'hole' to about 3/4 of the depth of the circular bore , i.e. not to the bottom of the circular part.
Last photo shows a piece of matching size WG. I think I understand that if I make a matching hole in the underside of the new WG, then blank it off and mount carefully over the slot/hole, I should be good to go.
Regarding polarisation, the back unit from which this lot was removed, does indeed have a sticker that indicated {horizontal} in line with the WG  assembly long dimension.

Thanks

Gareth

-- 
Mark  GM4ISM
gm4ism@...
dc2light.co.uk

Thanks Mark, That makes sense. I can drop the WG through the existing flange until it meets the junction, then fit either a flange for my SMA to WG transition, or end stop the open WG and fit a SMA feed there directly.
I assume polarisation will 'turn the corner and come out horizontal? My dish mount (as I want to use it) does not lend itself to a 90 degree rotation, but I can easily machine the feed to allow a 90 degree turn if needed.
Gareth

Hi Gareth,

I modified two of these now to fit wg42 transitions. Still to test but am hopeful they will be OK

Rob G7MHF

Progress, just need to soft-solder the lower flange for security. Don't want any of the power escaping.....
Then to mount the transverter if possible using the original ODU clip arrangement.
Gareth

Well that's gone well. Longer 'packed-out' screws from the original needed as the flange it secures is thicker. Only two fitted as it can't really go anywhere. As I had the parts I made myself a SMA/WG launcher to data here http://www.w1ghz.org/QEX/Rectangular_Waveguide_to_Coax_Transition_Design.pdf table on P17.
Now to investigate holding the whole lot onto my dish....
Gareth