[amsat-bb] Re: beginner question re: uplink power

Sun Oct 19 13:06:30 PDT 2008

Very good points, Tim.

Comments on vertical antennas.  First define vertical:  1) If you are 
referring to a high-gain FM base station antenna, then I would NOT 
recommend using one (because the gain compresses the signal pattern 
down near the horizon - for better repeater operation at long 
range).  2) If you mean a simple 1/4 wavelength ground-plane whip 
(like a 19-inch mag-mount attached to a square of sheet steel for the 
ground-plane), then (if used with a preamp) it will work quite well 
at either 2m or 70cm on Leo's.

Of course you need to use a preamp for the freq. band you desire to 
receive.  I used a 19-inch mag-mt with P432VGA preamp to collect UHF 
telemetry from AO-51 shortly after launch.  Also obvious is the need 
to provide bypass switching for preamp if you anticipate using the 
antenna for transmitting.

The M2 eggbeaters are probably slightly better than (and a whole lot 
more $$$) a 19-inch whip as are other more advanced omnis such as: 
Lindenblad, and Quadrafillar Helix.  But a simple little mag-mt 2m 
whip works great (especially with a preamp).  For a home-based Leo 
station, I think they are fine.  For portable (standing in the 
parking lot) operation the handheld Arrow is hard to beat.

For hard-core operation using Oscar-0, may I suggest what I am 
currently building (tongue-in-cheek):
http://www.kl7uw.com/eme1296.htm

73, Ed - KL7UW

At 10:05 AM 10/19/2008, n3tl at bellsouth.net wrote:
>Paul and all,
>
>I would be curious to hear from anyone currently using verticals 
>with preamps as their primary receive antennas. I have hesitated to 
>respond to your initial post, Paul, because (1) I am very new to the 
>satellites; (2) as a result, my personal experience with antennas 
>involves only the Arrow handheld antenna, the eFactor 0-gain omni 
>antenna, the Elk dual-band log periodic an MFJ mag-mount dual-band 
>vertical for my vehicle, and HT-specific antennas (Pryme AL800, MFJ 
>1715 and 1717, etc.); and (3) my other knowledge regarding using 
>omni antennas for satellite work is limited to what I have read here 
>and elsewhere on the Internet.
>
>All of that being said, I believe I would opt for something other 
>than a vertical - even with preamps - as my prime base-station 
>antennas for the satellies. I haven't yet built one of the Ramsey 
>preamps, but I intend to as the weather turns cool here in North 
>Georgia and I spend more time inside. I am curious about its ability 
>to improve reception for me with the sFactor, which is an 
>outstanding transmit antenna for reaching the satellites - based on 
>my experiences with it. I also logged more than a dozen contacts 
>involving AO-27, AO-51 and SO-50 using the eFactor with an HT as a 
>handheld antenna. My personal experience suggests that a preamp 
>would help it on the UHF receive side a great deal, although it 
>honestly exceeded my expectations - given the physical size of the 
>UHF part of the antenna.
>
>The N3TL handheld station has worked 46 states, VE1-2-3-4-5-6-8-9, 
>Mexico, Venezuela, Barbados and marimtime mobile stations all on 5 
>watts' rf out or less. It also has worked 20 states, Ontario, Mexico 
>and Venezuela on .05-watt (50 milliwatts) on the same set of 2 AA 
>Duracell batteries. For the sake of perspective, I made my 
>first-ever satellite contact on June 28th of this year - less than 4 
>months ago.
>
> From here, output power isn't the issue. I believe your money and 
> time will be best-invested in optimizing the receive side of your 
> satellite station.
>
>Best of luck with it, and 73,
>
>Tim - N3TL
>AMSAT Member No. 36820
>Athens, Ga. - EM84ha
>-------------- Original message from Edward Cole 
><kl7uw at acsalaska.net>: --------------
>
>
> > At 09:30 PM 10/18/2008, 12.01 wrote:
> > >hello,
> > >
> > >I have a beginner question. I am in the process of setting up my first
> > >satellite station. My initial investment is minimal and I have chosen
> > >to start out with a pair of 2m and 70cm omni antennas on the roof. To
> > >help out a bit I am also adding a mast mount preamp on each antenna. To
> > >protect the preamps they will be switched out of line by a RF sense
> > >switch (one for each amp). For reference the two preamps and the pair
> > >of RF switches are all made by Ramsey (I know there are better preamps,
> > >but not available in my current budget). I am keeping this initial
> > >adventure limited to the LEOs (and ISS, etc.).
> > >
> > >_The question: _ When I assemble the RF switches I must choose a RF
> > >range for the switch to work within. The range is determined by the
> > >choice of a specific resistor. The default three ranges suggested are
> > >0-10 watts, 10-30 watts, and 30-100 watts. I would be able to change
> > >the range later but it would require removing the unit from the mast.
> > >
> > >So... not having any experience (yet),_ what uplink power range is
> > >recommend for non-gain antennas?_ Is there one range that should cover
> > >the LEOs? If not, how much should I expect the required uplink power
> > >needs to vary across various satellites? Is it different for each band?
> > >I have read that it is always best to never be louder than the beacon
> > >and that's fine. I'm just needing to know where to start off my
> > >hardware choices.
> > >
> > >Thanks in advance for any help from you folks with the know-how. I look
> > >forward to a qso with you.
> > >
> > >.paul ac0z
> > >_______________________________________________
> > >Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
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> satellite program!
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> >
> > I'm surprised that you have had only one reply. I am not QRV on the
> > Leos so my advise is not as good as what you might get. My
> > "understanding" is that one can work most of the Leos with power
> > <10w. This is IF the stations on the bird also comply by not using
> > more power than is needed. If a "power war" ensues to try to capture
> > the satellite then running low power may be less effective to "break in".
> >
> > But seeing that so many folks run HT's that typically are 5w, I think
> > you might chose the lowest range as long as your equipment output
> > matches. You have to consider that you will have no antenna gain
> > using omni-directional antennas so uplink RF power needs are
> > affected, accordingly. NOW if some experienced sat op will add their
> > input on this subject you should have the info you need.
> >
> > I wonder if the Ramsey preamps allow for "hard" switching. That is
> > by separate control line that the radio PTT controls. Then You have
> > no issue with RF power and would run the units with the RF sense
> > disabled. I should state that "many" (dare I say most) experienced
> > VHFers that run high power (>100w) use hard-wired switching. I know
> > of NO eme stations that use RF sense control lines.
> >
> > PS: when my standard AO-10/13/40 ground station is re-installed I
> > will have available 5-60w with 16.5 dBc UHF uplink (all-mode).
> >
> >
> > ***********************************************************
> > 73, Ed - KL7UW BP40iq, 6m - 3cm
> > 144-EME: FT-847, mgf-1801, 4x-xp20, 185w
> > 1296-EME: DEMI-Xvtr, 0.30 dBNF, 4.9m dish, 60W
> > http://www.kl7uw.com AK VHF-Up Group
> > NA Rep. for DUBUS: dubususa at hotmail.com
> > ***********************************************************
> >
> > _______________________________________________
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