[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: Expected noise results with Drake converter (no satellite.)



Ed

Don't give up on the DSS dish. I followed your advice and had mine working
on this morning's pass. Copied the Beacon and I8CVS at MA 106  Range 59 K. I
haven't got any numbers but it doesn't perform as well as the BBQ. However I
think it would be usefull once I use a pre amp.  The dish I used was surplus
from a  friend and  is sold here by Bell Express VU . It  looks like the
original manufacturer or distributor is DISH.  I snapped open the plastic
housing and removed the original LNB. Made a woodedn plug to replicate the
lower half of the LNB and provide mechanical connection to the original
support arm. I wound the helix using 1/8 in. o.d. copper tubing available
from an auto supply store. By flattening the end it and drilling a hole it
made a nice spade lug fit over the center conductor and close enough to the
reflector for the matching element.  It is self supporting on the N
connector mounted on a 3 in. circular reflector. Ended up with 5  1/2 turn
helix. I was waiting to cut it at 5 but since it worked I left well enough
alone.

The helix fits nicely inside the plastic housing with the reflector sitting
outside the rear of the housing. I will try to fine tune it on future
passes. These 2 AM local antenna projects in the back yard are taxing.

Oh yes! I did note I had to lower the elevation by a few degrees from what I
thought was the same elevation I was using on the BBQ.


Thanks for your advice  73 Barrie VE3BSB

----- Original Message -----
From: "Edward R. Cole" <al7eb@ptialaska.net>
To: <amsat-bb@AMSAT.Org>
Sent: Sunday, May 20, 2001 6:25 AM
Subject: Re: [amsat-bb] Expected noise results with Drake converter (no
satellite.)


> Al and Hasan,
>
> Eary this morning, after trying my 18 inch DSS RCA dish/5-turn Helix/Drake
> [435 MHz IF...xtal changes only], 50-foot Rg-213 [2.5 dB loss], to a
> FT-736R [a freind's], I have to report total failure to hear the beacon!
I
> then subtituted a BBQ style dish with 21 dB gain and dipole feed, and
could
> just detect the beacon about 1-2 dB above noise.  This at about 63,000 km
> and squint ~6 degrees.  This is not quite the expected and estimated 7 to
9
> dB S/N!!!
>
> Not sure what the problem with the offset dish/helix is: pointing
probably,
> feed adjustment, bad feed [swr?], not enough antenna gain, too high NF,
not
> the expected IF gain from the Drake, ...?  All the above?
>
> I was visiting the qth of my freind Mike, WL7BQM, and his Meyers dish [~24
> dB] dipole combo, Conifer preamp [NF?], Rg-6 coax, FT-736R is doing
> fantastically well.  We heard the beacon from 25 to 35 dB above the noise.
> He has 100% copy on the TLM with ao40Rcv.  We had fun working a few
stations.
>
> So folks, there is theory and there is reality.
>
> I'm back to the "drawing board" and the bench.  Waiting for my Kuhne
> preamp.  Looking at setting up a 4-foot dish.  Wondering why the little
> dish performed over 35 dB down from Mike's system?  As they say...stay
> tuned for future developments.
>
> Ed
> Al, with no satellite you should see a significant rise in Rx noise when
> you turn on the preamp.  I see about two s-units; some see up to S-9!
>
> >

----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home