Re: dish building


g0ewn191 <g0ewn191@...>
 

Hi Chris--I was interested in the thread on dishes and the various
replies you received as I hope to try EME sometime---hopefully next
year. I also have been wondering whether to build, buy a kit, look for
a surplus dish or buy a petalised TVRO dish. A lot depends on the
following.

1. The frequency or frequencies you intend to use.

2. Is the dish mainly for tropo or EME.

If you are mainly interested in the lower bands---23 & 13cms then 4m
is a good size. However a dish this size made from GRP would be quite
an undertaking compared with more common stressed dish made from
alloy. A solid dish this size would be subject to some very strong
forces even in light winds. Reading your post I got the impression
(might be wrong) that your intended use is for a tropo system. If this
is the case you might be interested in using a plane parabaloid fed
with a twin double quad feed. If this sounds gobledigook look up an
article by G4CYA, Chris Otley. I had some input to this design though
Chris built the working unit and wrote up his work on his website. If
your intended use is tropo this antenna has a number of advantages:
ease of contruction and wider horizontal beamwidth. Look at the
article--it should be easy to scale for 4m and could easily be made
sectional for transport.

If you are mainly interested in the higher bands things are more of a
problem as the profile of the dish becomes more important. Upto 6cms a
dish with fine mesh would seem a good bet. Along with the info you
have already been supplied with, check out SAMI Dishes. This company
do a very nice 3m dish for around $700 (£350) though shipping and
import might double the cost. ( Still cheaper than 3m RF Hamdesign I
seem to remember). I'm not aware of a UK supplier of similar dishes.

At 10ghz or above 1.8 and 2.4m sectional dishes are available--best
price currently around £140 (2.4m) from a company in N. Shields. Most
commercial dishes have f/d ratios around .4 making them suitable for
EME---making your own dish would give you freedom to design the f/d to
match other feeds.

Good luck with your project--whichever route you choose. Please write
something up for Scatterpoint when you have an operational unit and
let us all know about it. 73s and best wishes Gordon G0EWN

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