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VK6 : Workshop in Perth next Monday night



This email is probably only of interest to amateurs in the Perth (VK6) area.
(To everyone else: Sorry for the bandwidth)

Inadequate Image Rejection in 2.4GHz Downconverters
===================================================
(or, "Why 3G has temporarily wiped out P3-D")

A Telecommunications Carrier has recently begun transmitting on frequencies
in the "3G" band, in the Perth area (and probably most metropolitan areas of
Australia).

Unfortunately, the lowest "channel" of these transmissions just happens to
fall on a frequency which is the first IF image frequency for 2.4GHz
downconverters that have 144MHz as the IF (assuming the usual practice of
low side LO injection).

Characteristics of the "interference" to such 2.4GHz downconverters is a
constantly (24 Hr x 7 day/wk) high noise floor (approx "20dB over 9"),
detectable across a bandwidth of approximately 4.5MHz

This coming Monday night (23rd June 2003), the VHF Group's feature topic
will take the form of a "workshop", encompassing:

1.  Explanation of the emerging usage of the 3G band in Australia
2.  The 3G bandplan
3.  Characteristics of the emissions
4.  Image Rejection performance of typical downconverters
    (including why the "interference" is the fault of the
     downconverter, not the fault of the 3G transmission)
5.  Effect of 2.4GHz bandpass filtering and/or
6.  Effect of 2.3GHz highpass filtering

We are currently trying to find a spectrum analyser that covers to 3GHz that
can be used as part of the demo;  if you can assist, please contact me
(vk6kch@amsat.org).

When : 7.30pm Monday 23rd June 2003

Where :  Wireless Hill, Almondbury Drive, Ardross (approx 10km SSW of Perth
CBD)

Who : Arranged by the WA VHF Group, but non-members most welcome too

How much : A few silver coins for Tea / Coffee;  otherwise, free


I look forward to:

a.  Seeing you there, and
b.  Hearing AO-40's beacon again :-)


73 Chris vk6kch





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