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

Re: Mode L uplink Question

>X-From_: hammond@surrealnet.net  Tue May 15 08:24:03 2001
>I had fun with a an 18" Dish Network dish and 2'x3' Primestar dish, using a 
>Transystem (moved to 144MHz, stub cut, thermistor added)--with and without 
>the little metal reflector.
>I'll post some pictures...nothing like electrical tape and zip ties at 1am 
>in the dark :)  Take home lesson?  The Primestar way out performed the 18" 
>dish.  I'm not convinced the 18" dish will be good enough for me (lots of 
>trees, etc) and the Transystem converter, unless the squint is excellent 
>and the view is open.
>I admit...I'm enjoying the dishes lots more than I had imagined!!
>Mark N8MH


That's interesting.  Sure others that are considering the 18 inch dish
appreciate the comparison.  However the Prime Star is twice the size so
will have ~6 dB gain over the RCA DSS dish.  I'm guessing you are using the
Transystem dipole feed.  Getting the feed positioned correctly on the RCA
DSS dish is tricky.  

I'm using the Drake converted to 433.9 MHz IF, with no RF or IF mods,
directly connected to a 5-turn helix feed [LHCP].  So  after reflection
from the dish it is RHCP.  Connected to the FT-817 thru about 4-foot of
RG-58 it drives the radio with one-to-two "bars" of noise showing on the

I built a diode [1N1005] harmonic generator and with -20 dBm drive at 800
MHz from an IFR service monitor I'm seeing an s-meter reading of 5 "bars".
When I drive the diode at 600 MHz at -20 dBm I get an s-meter reading of 3
"bars".  No discernable signal is heard with 400 MHz drive.

I can reduce the drive to -50 dBm at 800 MHz before reaching noise
threshold.  The Drake has a small screwdriver pushed into the N-connector
center pin and is placed about 1/4 inch from the diode, which is mounted on
an SO-239 panel connector paralleled with five 47K resistors to ground.
Not a very scientific measurement, but at least it confirms the Drake is
working.  I found 2400-->433.832 and 2401-->434.832.  Entering 600.3295 MHz
on the IFR [for 2401.318] I get 435.150.00.  After an hour of warm up that
drifted up to 435.150.50 and then held stable over two hours.

When I was listening last night and this morning I was looking around 433.9
MHz, so I was low about 1 MHz or so.  No wonder I heard nothing!  So this
will eliminate a couple issues and I can deal with dish pointing.  What I
need next is to try the diode with 2w at 50 MHz and see how strong the 48th
harmonic is.  If i can produce a strong enough signal then I might use it
for determining my dish heading.

Other news:  DEM called and my 144/1268 Tx converter is to be shipped today

To return to the topic  Mark wrote about, if the 18 inch dish proves too
small, then I have a 33 inch "Home-Dish Network" dish.  I'm hoping the
preamp will make up the difference.  It should arrive this afternoon.


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