Tuesday, 6 August 2013

DATV-Express pwr vs frequency

I just thought you might be interested in the saturated carrier
output tests I have been doing recently on DATV-Express.
There is a 3dB resistive pad on the output of the board for
the protection of the board and better termination of any
following filter.

Frequency MHz   Power dBm
65                         16.03
70                         16.54
72                         16.77
144                       17.70
148                       17.68
420                       17.97
450                       18.02
900                       17.65
1200                     17.39
1320                     17.62
2300                     16.16
2450                     15.20
2480                     14.66
2500                     14.36

The lowest frequency I could get the board to lock was
65 MHz and the highest frequency 2.5 GHz.

I also have a set of preliminary data for carrier leakage and
unwanted side band suppression. The testing methodology
used by me was a bit suspect but the figures are in line with
the figures quoted by the manufacturer of the modulator
chip and are more than adequate for DATV.

I have also been playing with Evanescent mode wave-guide
filters for 5.7 GHz. These are simple to build filters that use
the cutoff effect of waveguides and resonators made from
the inductance of the  wave-guide and the capacitance of a
tuning screw. Unlike most of the articles on this topic I have
not used surplus wave-guide (which I could not find) but
instead have used stock rectangular aluminium tubing and
brass bolts. I shall revisit this topic at a later date.

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