Go on then, I will bite to your reply, what part do you not understand ?
OK, a couple of days late, but only because I have been trying to locate the catalogue I used to have, dated 1996 which had all models, schematics and the one offs produced by Precision Metal. It may have been cleared out though I am almost certain I had uploaded it to the forum at some point in the past.
Anyhow to counter your claims of earlier
Thank you for taking the time to measure the dish, it looks to be a Precision Antennas 3.7m dish. I have just checked the original Precision Antennas catalogue and the only size listed larger than 3.7m was a 4.5m. The next size lower in the Precision range was 3.0m
Without the catalogue I cannot confirm this, though I believe the company would manufacture 4m and 4.2m antennas to order.
Your 3.7m dish has the same focal length as the Precision 2.8m and 3.0m dishes at 1207mm. The difference between them apart from size was the location of the 3 x press stamped feed support holes on the dish surface, they get closer to the edge as size increases. All three dish sizes shared the same length of feed support arms.
Whilst the first sentence is probably true, Prodelin also make a range of prime focus dishes of 3, 3.4 and 3.7m where the focal distance remains the same, there are minor adjustments that can be made to each feed arm (x4) in order to peak the boresight (clevis bolts), and allow changes to the feed type within similar models. With Precision (and probably Elite) feedhorn designs the three studs are fixed within the aluminium scalar rings, fixing the angles at which they can be bolted to the reflector surface.
As such if a larger diameter of dish is selected, simple geometry will confirm the last statement must be false since only a circle retains the same length to the focal point independent of the cross section selected. A parobolic surface cannot have similar feed support arm length with changing diameters.
Picture attached to clarify.
The Prodelin feed rod numbers are, 0176-214 for the 3.7m but once you look at the manual for the 3m/3.4/3.7m you see the part number is marked as 'varies' on Page 26.
Their 4.5m antenna, which shares the same inner reflector surfaces as the 3.7m (hence the same parabolic formula), has a different feedarm length and appropriate part number - 0176-225 which would suggest it is highly unlikely Precision/Elite had identical support arms for each of their larger products, but willing to be corrected on this.
Does anyone have any information on the relative performance of the Prodelin 4.5M and Patriot 4.5M dishes on Ku band. On paper the Patriot is better but a Prodelin dealer has said that the Patriot figures are not correct (he would wouldn't he !). Geoffrey
www.satellites.co.uk
One other item that could have been proven with the 1996 catalogue would be the different feed arms supplied by Precision for C and Ku band variants, since the holes in the reflector remain the same, there must be a difference in the lengths to allow adapters for the same focal length, but accomodating the scalar ring at the lower frequency. I might have a C band version of the 90cm model here (used for Gorizont 11W all those years ago), but it will be near or at the back of the garage.