Topics

Dish

Trevor David <tdavid@...>
 

Hi

I have one of RIGs 1mtr dishes with the coffee can on the end, can this be used for the reception of MSG, and if so what other items are required? It seems a waste to get rid of it only to replace it with a smaller dish

regards

Trevor

Ian S Deans <ian@...>
 

Trevor,

This will be a prime focus dish with no arm, so the answer is no it cannot
be used. You could probably pick up an old Sky analogue 80cm dish for next
to nothing, although they were more in use in Scotland as most of England
used 60cm dishes in the analogue days.

Regards

Ian.

Trevor David <tdavid@...>
 

Ian

Very many thanks for your reply. It will be turned into a pond now.

Trevor

----- Original Message -----
From: Ian S Deans
To: MSG-1@...
Sent: Wednesday, November 05, 2003 1:47 PM
Subject: Re: [MSG-1] Dish


Trevor,

This will be a prime focus dish with no arm, so the answer is no it cannot
be used. You could probably pick up an old Sky analogue 80cm dish for next
to nothing, although they were more in use in Scotland as most of England
used 60cm dishes in the analogue days.

Regards

Ian.



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johnrigsec@...
 

In a message dated 05-11-03 10:53:41 GMT Standard Time, tdavid@...
writes:

Hi

I have one of RIGs 1mtr dishes with the coffee can on the end, can this be
used for the reception of MSG, and if so what other items are required? It
seems a waste to get rid of it only to replace it with a smaller dish

regards

Trevor
All,

Trevor's original e-mail and Ian's reply got me thinking.
Firstly of course, you should have been able to use a coffee can (1.69 GHz)
feed
with MSG-1 dissemination but owing to that satellite's inability to
disseminate, via
direct reception, imaging is being disseminated via the EUMETCast DVB service
on
Hot Bird-6 at 13 deg. east (at Ku-Band) [and you can't use a coffee can!].
1.69 GHz MSG direct dissemination may not happen till MSG-3 - at least - I
understand, the Ku-band EUMETCast service continuing till at least that time.

Now I know I should know this, having been operational in satellite TV since
the
early 80's, but am not sure.
I suspect someone out there will be able to give the definitive answer.

When I began receiving C-band satellite TV back in the early 80's followed by
Ku-Band reception, I used prime focus dishes and head end feeds and equipment
designed for prime focus dishes.

When DTH took off, the offset dish and LNB took over from prime focus.
Now, the offset dish is elliptical and the LNB (at the focal point) is below
the dish
pointing up into it.

Question.
Is the modern LNB specifically designed (geometrically) to work with an
(elliptical)
offset dish?
Or, can you also place it at the focal point of a prime focus dish?

You can successfully mount two (or even three) LNB's on a fixed offset dish
(spaced
on the LNB arm) of say 85 cm to receive satellites at various locations.
In my case, currently, Astra at 19.2 E and Hot Bird at 13 deg. E.
I tried dangling a Ku-band LNB - slightly offset in azimuth, next to the
coffee can feed
of my 1 m Meteosat-7 dish (pointed at 0 deg.) just as an experiment and was
able to receive Hot Bird (analogue) TV transmissions from 13 deg. E at the same
time,
noise free.

So, does anyone know about the design of the modern Universal Ku-Band LNB
feed geometry?

Regards,
John Tellick.
RIG.

a_van_belle
 

--- In MSG-1@..., johnrigsec@a... wrote:
Question.
Is the modern LNB specifically designed (geometrically) to work
with an (elliptical) offset dish?
Or, can you also place it at the focal point of a prime focus dish?
John, Offset dishes may look elliptical but seen from the sat (or
from the LNB) they are ROUND !

Modern LNB's are only suited for offset dishes. The feedhorn is
different to get a smaller beamwidth, compared to most prime focus
dishes with F/D=0.5 (offsets have F/D of 0.6 to 0.7).

You can put a modern LNB in the focus of a prime focus dish, but you
will only use 40 to 60% of its surface, giving low signal level.

With Eumetcast on the low band (11096 Mhz) you may be able to find a
used "old type single band" LNB with a scalar feed ring assembly and
H/V servo mechanism or Ferrit H/V switcher.
But you will be shocked by the noise figure of these oldies, 1.3 to
1.8 was excellent these days !
Nowadays you have 0.6 to 0.7 dB for 1/5 of the price !

Another drawback of Prime focus is that they do gather snow !
At 1.7 Ghz this is no problem but 2 cm's of snow in the dish can make
your a 11096 MHz signal disappear completely.

Greetings,
Arne van Belle

johnrigsec@...
 

In a message dated 07-11-03 04:54:59 GMT Standard Time, a.van.belle@...
writes:

Modern LNB's are only suited for offset dishes. The feedhorn is
different to get a smaller beamwidth, compared to most prime focus
dishes with F/D=0.5 (offsets have F/D of 0.6 to 0.7).

You can put a modern LNB in the focus of a prime focus dish, but you
will only use 40 to 60% of its surface, giving low signal level.
Arne,

Thanks for your useful information.
I knew there was a difference between (early) prime focus RF equipment and
present
day offset equipment but not sure quite what.
I suspect I'm not the only person to learn something new.

My early prime focus LNC's (as they were called in those days) have wider
apertures
and scalar feeds.

But you will be shocked by the noise figure of these oldies, 1.3 to
1.8 was excellent these days !
Nowadays you have 0.6 to 0.7 dB for 1/5 of the price !
Indeed, my first 10/11 GHz LNC from Avantek had a noise figure of 1.8 dB and
cost,
in 1986, £1,200!

Sorry, a bit off topic for MSG, but it was through C-band and Ku-band
satellite TV
that I got into weather satellites.
And the rest, as they say, is history.

One thing, for us in the UK who are only supposed to install ONE dish per
property,
take a look at the ultimate(?) multi satellite dish system at <A HREF="www.wavefrontier.com">
www.wavefrontier.com</A>
you can have your (multiple) satellite, satellite TV and EUMETCast, from one
dish!

Regards,
John.
RIG


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