archie.hackett at hotmail.com
Fri Oct 19 11:18:02 PDT 2007
You wondered if I¨d share with the other satellite enthusiasts a few words about my equipment.
> Having read your prior e-mail "AO-7 report" and the warnings about
> running too much uplink power .... and using better receive,
> I wonder if you would share with the readers what antennas, power at
> antenna, resulting EIRP, and receive antenna and preamp you are using on AO-7.
> Maybe your example will help folks figure out what they need to
> do. You probably remember that I have hammered on about using a
> preamp (at the antenna) for years on this reflector.
Certainly Dave, happy to oblige.
First it must be noted, as I've been waffling on about for donkey's! years (Manchester slang = a long! time) that you *DO NOT* have to affluent to have a fully automated satellite station ... (nor does one need to be fully automated) ... that's just a "convenience".
Let me also say, that if I could afford one of the "all singing, all dancing fully automated rigs with a CAT interface, I'd buy one, it's just that I've never been able to afford !!! one. My QRP power levels are not *ONLY* due to my being "sensible" ... (note the parentheses) ... the main reason has always been lack of availabler funds for satellite gear. One of my first "OBSERVATIONS" was entitled "Oscar 13 on a Shoestring" ... I digress.
The radios are the FT-290/790 pair, now well over 20 years old but still providing adequate service. For AO-7's uplink the FT-790 feeds a modified Norwegian Telenor mobile base station amplifier that originally operated on 460Mhz. I hack-sawed off the first two stages, added a 6dB pad, "tweaked" the filter and fed it with 200mW from the 790 to produce 8 watts. I have 6dB of loss at 70cm with the RG-214 coax ... (scrounged from the oil industry installation here) ... so I have an EIRP of about 20 watts from the elliptically polarised home brew 2 x 6el beam. I have never found an elevation rotor to be a necessity.
The 290 for AO-7's downlink is preceeded by a home brew BF981 preamp mounted at the aerial. At 2m an
ultra-low noise gaAsFET preamp in my opinion is not necessary ... due to the inherant sky noise of approximately 2dB at 145Mhz *IN CERTAIN PORTIONS OF THE SKY* ... though at microwave and above, where the sky is quieter, they are a must.
For LEO's, more important than a preamp IMHO is a polarity switcher.
The debate of circular polarisation vis-a-vis ellipticasl can be found on the website ...
The aerials at ...
... at the bottom of the page.
For AO-7 at 1400-1600Km above the earth you don't need to bother too much about doppler correction but for LEO's like VO-52 that literally streak across the sky some sort of auto-doppler tuning is recommended.
Even newcomers will be aware of the "One True Rule" ... (doppler tuning). This is all very well if you do! have the latest all singing/all dancing rice-box but what do you do if you operate with 20 year old rice boxes that don't have !!! CAT tuning?.
You use a program called InstantTUNE together with InstantTRACK which allows automated doppler tuning using mic pushbutton rigs. Instantune only allows tuning EITHER the uplink or the downlink so if you want to be FULLY automated, you'll need a pair of old 386 IBM's (or equivalent) and a pair of monitorsd from the nearest computer company/school skip.
Everything else I can think of is home brewed and is to be found on the OBSERVATIONS page mentioned earlier.
A couple of useful links are ...
... which illustrates what can be done with QRP and a shoestring buget.
... everything you ever wanted to know about AO-7 is on this site ... I know, cos' I maintain it.
If it's not there, ask me, it'll be in my archives.
You'll find a lot of useful information here ...
... and it's all free.
I hope this mail illustrates thast it is possible to operate amateur radio satellites on a shoestring buget. Remember, a *BIG* signal is not necessary a good signal.
Have a nice day, all.
73 John. <la2qaa at amsat.org>
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