Re: Re elevation on a dish


Hi John,
The 12 food dish sounds amazing. It must have had a very narrow focus indeed. It was good to know that a metre of waveguide is still good for a terrestrial system. I am looking now at the mechanics and hopefully will have a system to go on a trailer for the summer with a dish above people’s heads. 
I guess we are spoilt these days with the modules from DB6NT, when in days gone by it was a lot harder to get a decent system together. 
Anyway thanks again for all the details .
Dave G4GLT. 

On 8 Jan 2021, at 14:13, John Fell <john.g0api@...> wrote:

Hi Dave ,
I had a 20W TWT based system up this mast for over 20 years before moving on to use bits of it for 10GHz EME at G4RFR .

The first G to G contact on 10GHz (CW) used the TVTR - 1994 between G4RFR and G3WDG , using 12 Ft prime focus 0.43f/D dish at our end.

The TVTR was quite a load for my 30Ft Western Ulimast and restricted other band antenna deployment a bit .....feeding all TWT rails up rotator style multicore cables ......
My TVTR used original G3WDG modules with a modified 4 port WG16 on its front end , with the 2 stages of LNA directly on the RX port and TWT output on the TX port .The feed was a G3PHO type WG 16 flanged and feeding the 4 port switch via EW90 elliptical waveguide .Probably had about 1 m total between the feed and the front end LNA .
For tropo use this still represents a reasonable insertion loss . You can easily make ur own EW90 flanges to marry standard WG16 flanged ports .
Form the required bends into the EW90 - using gentle bends by hand /vice.

A 10W system at the dish will form a potent terrestrial system , but do spend the time to Engineer the housing to prevent condensation .An inverted bucket format is good as it allows airflow and if you take all services in via the open end rain tends to stay out .( worked a few with 10W TWT last year on the 12Ft dish - on 10GHz CW ) . The 200W TWT makes for louder echoes though .

From home I am only operational on RX on 10GHz , but having £10 LNBs and GPS reference locking makes it a potent and cheap thing to do .


On Fri, 8 Jan 2021 at 11:33, Dave via <> wrote:
Hello John,
Thanks very much indeed for photos of your system. Yes, I take your point about spacing the dish far away enough to get 30 degrees of elevation. I am torn between using a  waveguide feed or preamp at the feedpoint.
I will look at the limits of the Jack very carefully in the workshop as you suggested. 
If your system has lasted for so long it must be very rugged and well constructed. 
Thanks again for all the pointers.
Dave G4GLT. 

On 8 Jan 2021, at 10:55, John Fell <john.g0api@...> wrote:

Hi Dave ,
Had to wait for the frost to lift to take these pics .
My masthead 60cm dish and Elevation system .

18" jack used with base end pivot made from 3" exhaust clamp around the standard Scaf pole mast extension above KR600 inside cage support ( just below bottom of pic).Extra large clamp allows one leg of U bolt to be fitted with a turned alum sleeve spacer to take the eye of the base balljoint of the jack.Also allows positional adjustment to set up desired stroke/maximum dish travel..

Top end of jack fits onto a welded pivot bolt attached to underside of a 2 x 1" steel hollow section , welded or bolted to a steel stand-off plate that has a steel hinge at the mast end .The other end of the hinge is welded to a steel Scaf clamp , which again can be adjusted to setup the final geometry .

The dish is mounted on 1.25" dimeter steel tube that came with it - in this case it is a 90 degree bent item so that is why the 2X1" hollow section is used to offset the dish tube and put the vertical load thrust on the centre line of the vertical mast .Room to add masthead PA/front end housings just behind the dish , without adding much loading to the feed arm etc .

You will notice the system puts the offset dish well forward offset to the mast - this allows the top rim of the dish to travel to an effective 30 degrees of Elevation .
That allows pointing at QO100 and well above ground noise sources for Sun noise  measurements and I have decoded DL0SHF several times over last few years .Other antennas on mast above are positioned to offset the dish system , again putting the vertical loading equally about the rotator cage .

The small box on a standoff 1"x1/8" aluminium flat bar just in front and below dish base  is housing a G4JNT AZ/EL digital sensor .

Which ever system you build make sure the jack is adjusted so its internal limit switches limit the travel within limits that protect the dish - I managed to fold this dish at the top with 12V supply and the only thing I noticed was a sudden rise in ground noise !

After 30+ years up the mast the only thing that needed replacement was the jack ( running leadscrew nut fractured ) -  the light coloured cylinder on the jack is an old aluminium Dow Corning Vacuum oil can - this covers the top end jack seal to prevent rain getting in when/if the seal cracks - smother all surfaces in Waxoil ....


On Thu, 7 Jan 2021 at 17:03, Dave via <> wrote:
I am adding elevation on a dish for tropo only (not EME) and wondered if anyone has a photo of the mechanics of it, preferably with some sort of hinge . I have an actuator which has a stroke length of 4 inches. I think the lower part of the dish will have to be pushed outwards.
Dave G4GLT.


Join to automatically receive all group messages.