Re: dish building


Chris Ruddy MM0KOS
 

Hi all

Thanks again for the replies, the dish would be used for EME and
its not just for me, there is a group of us with a good mixture of
bands and knowledge on HF, VHF, SHF all the way to laser. The main
reason for asking was to get the up and down side of others
experience in building or having bigger dishes, now i can see or
best think, the best way to go is a stressed mesh dish but this
depends on the location we choose for /p work and how exposed it is
to the WX in GM. We intend to use it from 23cm upwards to 10ghz for
EME but we also have beams for 23cm for tropo use, maybe at a later
date we will consider higher bands.
I am just about capable of 23cm EME if I get my finger out and
complete the 2x GI7B amplifier, build the dish i have here and mount
the allready built septum on it.
I have also looked at patch feeds for multi band purposes and have
build one for 23cm but dont know how successful it will be, i need
to get a spectrum analyser on it and have a fiddle to see if it will
perform, if not ill try again and then try other bands on it too.
With regards to scatter point i would be more than happy to write a
small piece for you on how we get on with the project but may be a
little time before we get fully going and hope to have some sort of
web page on line soon with pages showing the current projects that
we are working on justnow

Thanks Gordon and all the others again 73 have a nice September
weekend




--- In ukmicrowaves@yahoogroups.com, "g0ewn191" <g0ewn191@...> wrote:

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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