single feedhorn for 1.80m Channel Master Prime Focus

jacqfranc

Hi Everybody,



Here goes a somewhat "difficult one":



I need a single polarity feed (part number 6777) for a 1.80 m prime focus / 4 petals Channel Master.



Bought in 1993, it is not made anymore and no spare parts seem to be available, according to Channel Master themselves (not very friendly at Pforzheim...).



Actual configuration: 0.6 wideband WR75 Gardiner LNB and mechanical polarizer with Echostar 7000 (model 3000 until 2001); very performing: in 1999 it was able to receive most Astra digital signals in Istanbul whereas most people needed 3 meter dishes and in Budapest, where I am for the moment, I almost get the V signals on Astra 2D (blocks, no more).



I would like to experiment with other LNBs but therefore, need that single one:



1) there was an article in the 12-01/04 issue of Telesatellite International on the REISAT servo polarizer (very expensive: € 1000 !) which rotates with a side - mounted servomotor



2) the same article tells us that, for extreme reception, mechanical or magnetic polarizers, "have disadvantages: in the wave - guide, or just behind it, antenna wires, coils and ferrite magnets can be found: longer signal paths and mismatching which are deadly for digital signals, are the result and there is the additional chore of aligning the small dipole in the wave - guide with the actual polarization plane from the satellite, since there is no fine skew adjustment available":



so, a test with a good C 120 LNB could be made (by the way: SMW offers a "quarterwave transformer", enabling the use of WR 75 with C 120)



Does anybody know where to find this feed or, who could make one ?



Moreover, does anybody have experience with the Astrotel 0.5 dB wideband WR 75 LNB ?



Thanks.

Old Satellite

Yes i Can confirm that the Astrotel 0.5 DB wide band lnb is both stable and is of good quality. not the best though but good.

I have two both on large dishes (3.7 and 1.8 mtr)

The feedhorn problem is a little more difficult however Astrotel, with ADL have several solutions for offset and Prime focus dishes

Check out the link at Patriot

http://www.sepatriot.com/commerce/dept.asp?dept%5Fid=7 here are several options for offset feeds.

There is an Astrotel office in the UK and prices are generally the same as the us price list.

Kind regards

Old Satellite

jacqfranc

Thanks a lot !

It happens that, yesterday afternoon, browsing through the web, I came across that patriot site AND THE ONE OF ADL ITSELF !

So, for all of us with similar problems: www.adl.feed.com is the company we need: they still make all the necessary feeds for that antenna, when using what they call an OP -120 mounting ring: the ones (see catalog) are KU - 901, KU - 850 and KU - 870.

I will contact them and keep you informed of their willingnes to sell what I need.

Thanks also for the comment on the Astrotrel.

A last question for everybody familiar with orthomode reception:

a) what is the best way to combine the 2 LNB's (1 for H and one for V) at the dish itself on 1 cable to the receiver (Echostar 7000) ?

b) does each LNB lose a lot of signal strength this way ?

Thanks and willing to be helpful when possible.

Channel Hopper

The 1.8m antenna (series 6318), came with a variety of feed options

6777 - single polarity
6774 - Dual polarity - useful to update for universal LNB
6779 - mechanical polariser

If these are really as rare as you say then the mechanical characteristic of the 1.8m with an f/d ratio of 0.4, should allow a suitable aftermarket feed to be sourced.

At the end of the day though, the four piece reflector design meant it was never an efficient antenna, even when perfectly assembled.

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