Isidro Berniol 2020/09/24 15:38
At this frequency range 1500Hz are nothing to care about.
Also if this are antenna duplexers, you can't tune them with the
nanovna. The filter points change with load and source complex impedance.
So you need to do the fine tuning with the antenna, cables, transceiver
and receiver in place.
You need to couple the measurement signals with directional couplers to
minimize the influence to the setup.
you can pretune a diplexer with a VNA, but the finetuning can only be
done with real loads, sources and cables.
On transceiver side put a power meter between transceiver and diplexer,
also between diplexer and antenna.
Use only high quality power meters with perfect rf shielding and very
low SWR.
Also use only double shielded cables between diplexer and rx / tx.
Also separate the two cables to reduce coupling.
Also inject via a directional coupler and some attenuators a signal
generator to the diplexte rtransmitter input at the receive rfrequency.
So you can tune for low loss on you tx frequency and good rejection on
rx frequency.
Also use a directional coupler or pick off in front of the rx input for
a spectrum analyzer. With the SA you can adjust fro tx frequecy
rejection and rx frequency pass.
The rejection of tx frequency at the receiver input is mor important
then the damping of the rx frequency, because most receivers are very
sensitive to rf blocking.
If done right it is possible to have only 1 to 2 dB receiver side
damping and some percent loss of tx power.
Have done such setups for mobile LMR basestations a lot of times. No
chance to have a good setup without finetuning of the individual setup,
but then there was allways a very good and reliable performace over many
years.
Also please use a antenna with low sensitivity to environmental changes
like temetature, snow, etc.
Isidro
DB1SBI
Am 17.09.2020 um 16:53 schrieb johnjgormley via groups.io:
> 452 - 457 MHz
>