Above is a
copy of the spectrum as received at my location; the centre
frequency is set to 145.700 MHz (my local repeater GB3AR). Notice
that the signal received at 145.700 MHz is as strong in both cases,
however even the signals at approximately 10MHz both sides of the
centre frequency are attenuated, with the signals in the region of
100MHz (FM Broadcast) are very low, as are the signals at 155Mhz and
signals at approximately 135 MHz and 153 MHz have been attenuated by
approximately –20dB and –35dB respectively. These strong signals,
being close to the 2 meter band, can cause interference.
reference, if 1 watt of power is reduced by –20dB the result is 10
–35dB the result is 0.316 millwatt (0.000316W).
transmit; any spurious emissions outside the pass band would also be
reduced by the above amounts, shown in the graph, thus keeping the
transmitted signal clean.
Amateur TV working, the pass band of
the 23 cms receive filter should give sufficient attenuation of your
transmitted signal, so that the received signal from the repeater
can be seen whilst you are transmitting. (A look through filter)
Look at ATV Filter page.