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Re: RE: Eagle



My own preference:  It depends.

If the bird is FM, then it is much easier to have the higher band be
the downlink.  It is easy to tune for doppler by ear on the downlink
(tune for best quieting) and let the satellite receive capture effect handle
the uplink doppler.  I found it was much more difficult to get into Mir's
70cm repeater, for example, because of the need to doppler-match the
uplink for the station's receiver.  Computer control is pretty much
required if the upilnk is on 70cm.  (yeah, I know lots of folks do it by
hand, but let's not push the walk-and-chew-gum-and-tune envelope)

Conversely, for SSB/CW, it is easy to tune & correct for the uplink doppler,
and being able to leave the downlink more or less stationary during QSOs
and for receiving beacon telemetry is nice.

But, there is a price to pay for ease.  The pollution we get on UO-14
from the unlicensed 2 meter stuff down south makes operating nearly
impossible at times.  I'd rather fiddle with the knobs more, and fight RF
pollution less, if I had to make that tradeoff.

Greg  KO6TH


>From: Jon Ogden <na9d@speakeasy.net>
>To: Estes Wayne-W10191 <W10191@motorola.com>
>CC: amsat-bb@AMSAT.Org
>Subject: Re: [amsat-bb] RE: Eagle
>Date: Wed, 18 Jun 2003 19:06:45 -0500
>
>Wayne,
>
>There's one more compelling reason to go mode U/V.
>
>It's doppler.  The V band downlink has less doppler shift than a U band 
>downlink.  And since you are generally supposed to tune the high of the two 
>frequencies you tune your uplink and not your downlink (except for those 
>using the "one true rule" on the computer).  So it's a little easier in 
>that sense as well.
>
>73,
>
>Jon
>NA9D
>
>On Wednesday, Jun 18, 2003, at 18:08 America/Chicago, Estes Wayne-W10191 
>wrote:
>
>>W4SCO wrote:
>>
>>If the uplinks are in the L and V bands and the downlinks are in the U and
>>S bands, I would be interested (L/U and L/S and V/U and V/S).
>>
>>Wayne W9AE replies:
>>
>>I'm curious why you have such a strong preference for V/U instead of mode 
>>U/V.  Most of us don't have a strong preference because we use the same 
>>radios and antennas for V/U or U/V.  But there are three compelling 
>>reasons why mode U/V may be preferable for Eagle.
>>
>>1. The path loss for the V-band downlink is less than for a U-band 
>>downlink.  When the satellite uses omni antennas near perigee, the ground 
>>station doesn't need as much antenna gain to hear a V-band downlink.
>>
>>2. V-band has high-power intruders in many parts of the world.  So a 
>>V-band uplink gets QRM from high power cordless phones and unlicensed 2m 
>>FM transceivers (these intruders can be thousands of miles from you and 
>>still QRM the satellite).  Presently there are few high-power intruders on 
>>U-band, with the exception of the PAVE PAWS radar that occasionally 
>>plagues AO40.
>>
>>3. Mode V/S doesn't make sense for most hams because virtually all of the 
>>available S-band downconverters use a V-band IF.  We would need two V-band 
>>radios, or we would need to get new downconverters.
>>
>>The old argument for a V uplink (mode J) originated in Japan where the 
>>populated areas had a high V-band noise level that made it difficult to 
>>use for weak signal reception.  Japanese hams preferred to have downlinks 
>>on the quieter U-band.  Things have changed since then.  Nowadays there 
>>are very few high power paging transmitters on V-band (the paging industry 
>>is virtually extinct).  And most V-band land mobile users have migrated 
>>either to cellular phones or to digital or trunked services on higher 
>>frequencies.  The result is that over the years V has become a more 
>>desirable downlink band because the urban noise level has dropped.  And 
>>over the years V has become a less desirable uplink band because of the 
>>growing use of high power cordless phones and unlicensed 2m FM 
>>transmitters in Southeast Asia and Latin America.
>>
>>Wayne Estes W9AE
>>Mundelein, IL, USA
>>----
>>Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
>>Not an AMSAT member? Join now to support the amateur satellite program!
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>>
>>
>-------------------------------------
>Jon Ogden
>NA9D (ex: KE9NA)
>
>Citizen of the People's Democratic Republik of Illinois
>
>Life Member: ARRL, NRA
>Member:  AMSAT, DXCC
>
>Ham Radio Webpage: http://www.qsl.net/na9d   <- Updated on 1/12/03!!!
>Digital Photography Page: http://homepage.mac.com/jogden/Photography.html
>
>"Between Stimulus and Response is our greatest freedom - the freedom to 
>choose."
>                                                                            
>                              - Dr. Steven Covey
>
>----
>Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
>Not an AMSAT member? Join now to support the amateur satellite program!
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