[amsat-bb] Re: Suggestions for Mode L antenna

Tue May 13 00:06:58 PDT 2008

Bob, Ron and Greg:

The problem we have at this point is that uplink and downlink 
performance has not been specified by the P3E team.  So, in my 
thinking, one can only go with the AO-40 experience for making 
enigneering decisions for your ground station.  On SSB I found that 
9.5w and 20-dBi (linear pol) was inadequate for AO-40.  It looked to 
me that I needed a minimum of 15w and more would have been 
better.  This is power at the antenna terminal not at the radio, so 
one has to calculate line loss.

For operating the Leos your uplink needs are probably less and I will 
leave it to experienced operators to state what that is.

Fortunately, Times Microwave gives you a wonderful on-line cable-loss 
calculator for their entire line of cables:
http://www.timesmicrowave.com/cgi-bin/calculate.pl
or you can download the zipped program to run on your local computer:
http://www.timesmicrowave.com/cable_calculators/

Plugging in LMR-400 x 50-feet at 1268-MHz results in 2.3 dB line loss 
or 58.3% power at the antenna.

Using my AO-40 requirement of ERP = 15w x 100 = 1500w:  One would 
want 25w at the radio end of the 50-foot cable.

Bob has this easily with his KJ6KO 60w amp with over 3-dB spare.  BTW 
my current 1296 setup uses 150-feet of 7/8 hardline with ~20 feet 
LMR-400 to give me 20w at the antenna (I have a KJ6KO amp as 
well).  For satellite, I will probably mount my 15w 144/1268 Tx 
converter at the antenna, thus eliminating expensive hardline.  I do 
that for my 435-MHz uplink by using a 50w brick at the satellite 
tower and using 125-foot of RG-213 to provide an input of 12w from my 
FT-847(50w).  I have an outside equipment box with 12-v power supply 
and room for preamps and coax relays:
http://www.kl7uw.com/sat.htm

Bob, you might be OK with a 16-dBic Helix considering the power you 
have.  A 4-foot dish is equivalent in gain to a 12-foot long Loop 
Yagi (20-dBi) and much harder to mount and aim, so my recommedation 
would be using yagis to get the gain (and be easier on your az-el 
mount).  If I recall the M2 yagi has that.  Don't forget that you 
gain a 3-dB advantage when using a CP antenna on Mode-L.  If you are 
going to use the dish for 2.4-GHz reception then dual-band use might 
be an advantage.

With Ron's 10w in the shack he will only have about 5.8w at the 
antenna, so you may need more gain.  For P3E this is most likely; for 
AO-51 that might be OK.  In any case I would recommend LMR-400, at 
minimum, as low-loss cable, or placing a brick amp at the antenna to 
boost up your power.  Note: Dale-KL7XJ runs 10w on 1268 to a helical 
beam on AO-51 so, without knowing his line loss, one might guess that 
50-feet LMR-400 + Helix will be adequate on AO-51.

73 Ed - KL7UW

At 11:15 AM 5/12/2008, w7lrd at comcast.net wrote:
>Hello
>Currently the way I have been doing L band is as follows.  IC1271A 
>(1.2ghz xcvr)  10 watts, KJ6KO 60 watt amp to a M squared 23cm22E2 
>yagi at 50 feet, through 50 feet of LMR400.  The yagi is at 50 feet 
>for terrestial L band.  When we get our next HEO (praying) I will 
>most probably put the 22 el on the satellite array at 15 feet with 
>the az/el rotor.  I have been able to work through AO-51 with the 
>current set up.  The power is enough so some RF gets squirted up.  I 
>am considering a helix for 1.2 for satellites, or even my four foot 
>dish.  So many choices <grin>.  Does anyone know  what the expected 
>ERP on L band should be??
>73 Bob W7LRD
>Seattle
>
>--
>"if this were easy, everyone would be doing it"
>
>-------------- Original message --------------
>From: Ronald Nutter <rnutter at networkref.com>
>
> > Greg:
> >
> > Thanks for your option. My antenna building abilities havent been the
> > best, so I am looking at commercially made antennas.
> >
> > What type of coax/feedline should I use ? I will probably have the run
> > under 50 ft. I would hope I dont have to use hardline as that will
> > probably be very expensive with the price of copper. As I get close to
> > the antenna, should I shift over to a different type of coax/feedline so
> > that I can rotate the antenna to track AO-51 ?
> >
> > Ron
> > KA4KYI
> >
> > Greg D. wrote:
> > > Hi Ron,
> > >
> > > I've done ok on AO-51 with a homemade helix. See
> > http://home.wavecable.com/~ko6th at the bottom of the page. I 
> also have watts
> > in the shack, but a full az/el rotor system. I don't know how 
> sharp the pattern
> > is for the helix, so I don't know how effective a fixed elevation 
> system will
> > be. But from the reports I've received, the 10 watts and my 60' 
> of hardline
> > with about 7 feet of RG-214 at each end seems to be quite adequate.
> > >
> > > Good luck,
> > >
> > > Greg KO6TH
> > >
> > > ----------------------------------------
> > >> Date: Sun, 11 May 2008 20:49:23 -0500
> > >> From: rnutter at networkref.com
> > >> To: amsat-bb at amsat.org
> > >> Subject: [amsat-bb] Suggestions for Mode L antenna
> > >>
> > >> I am considering purchasing the 1.2 ghz module for my IC-910H. For my
> > >> satellite work, I have my antennas angled at about 20 degrees since I
> > >> dont have an az/el rotor. This setup worked reasonably well with Mode S
> > >> this weekend. What are my chances to be able to work Mode L with this
> > >> kind of setup ? Also, I would appreciate any suggestions for an antenna
> > >> that I could use. With only 10 watts, I am not expecting a great signal
> > >> but I would hope to have at least a readable signal. Also, would
> > >> appreciate any suggestions as to coax/feedline that I should look at
> > >> buying ?
> > >>
> > >> Thanks,
> > >>
> > >> Ron
> > >> KA4KYI
> > >> _______________________________________________
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> > rive_052008
> > > _______________________________________________
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