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RE: Eagle



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
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