posted here for the benefit of all the non-RF people :
Hi Alan. OK roger all that. as you know, duplexors, cavity filters, bla
bla are my home game...
if you have interaction problems between them the cable lengths are
wrong between the filters.
IE the coupling is wrong.
with a single filter, with loops lined up in line, can you get good VSWR ?
lengths : Stay away from half waves (in coax) and super short lengths.
If it was designed for UHF, the lengths will be too short. .
depending on how you have the loops configured, a quarter wave in coax
is a good start and what I would recommend .
Also, are these bandpass or bandpass notch ? They will need to be
bandpass notch otherwise you will not have a hope of making rejection /
insertion loss.
they can be made BP-N without difficulty.put T adaptors on the tops of
each filter loop connector, (IE a single loop is used), and a high
quality series cap inserted in series with the loop in the can) to
generate a zero.
AND just use good quality RG58 for interbay.... cable leaking is a huge
load of BS, especially when there is a antenna just nearby . ha ha I see
people touting their 140dB isolation cable when the antenna is about
20meters away...
BTW I wrote a T800 windows programmer...
I can come up there some time with one of my VNAs.... you are not far.
On 16/07/2020 10:49 am, Al Beard wrote:
Thanks Glen,
This bug wasn't going to be a "show stopper" as my intended
receiver is an SSB one with no squelch or mute. With a FM
transceiver, muted audio maybe the only one available lest
the radio speaker would emit annoying noise all the time.
BTW: My development here atm is on the Banana Pi M2 Berry with
a 300Gb SATA laptop hard disk, not an SSD. All in a Tait T800
series module box. The T800 2m system is ready. Synthesized,
all 144.025 to 147.975 channels are in the eprom, Rx & Tx.
21.4 MHz IF.
A cavity set is a problem, I have a set of six 6" RFS 3/4 wave
70cm cavities that on 1/4 wave tune to 145 - 148 MHz nicely.
On making coupling loops and inter-cavity leads, have difficulty
with interactions. Also need better test equipment to resolve to
a 100db notch. Or at least 80db, ie. two cavities let alone three.
On 16/07/2020 8:31 am, glen englis
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