Hi Ian,
Thanks skip 
 
A lot of us in the US have to sit back and look at the
information you wrote and do the translation to values
we have here in the US. (... he says laughing to himself)
 
There are a hundred plus questions that need to be asked
to get the best picture of what's going on with your
repeater system.
 
Your mention of the "rx scratch" without a transmitter
On is key issue. You don't say how much other rf is
in the area?  ... at other sites?  ... or what else is
in the area.
The nearest repeaters near my tower are over 1km away
 
A few things come to mind first..   First the antennas are
omnis and have you tried changing them around to the other
repeaters?
Looking into trying that
 
Do the antennas have a true DC ground return path? Are
the antennas fiberglass radomes (covers) or are they
The exposed metal type construction?
Fiberglass
 
The notch pass duplexers might be a larger issue if
you hadn't said the tx doesn't have to be on for the problem
to show up. But the duplexers might not have a true dc
ground path through the probes/loops.  You might check for
That.
When B repeater is operating and one of the other repeaters come online then it doesn't affect  B's transmission and vise versa.The scratch seems to only affect a particular repeater when its operating .It doesnt seem to be a intermod / interference  between repeater problem
With one of our rf companies over here advise to go to band pass,band reject over notch diplexers when on community sites.The 2 vhf repeaters that i advised (A+B) have notch tins (one connection in top) but also have a small hole in top with a tunning cap notch .The diplexer feedlines are rg214 on both of these repeaters as the new diplexer on D are N connectors direct to RG223 patch leads to the repeater and it seems to work ok
 
Does the feedline/coax have grounding kits on them?
Not yet but looking into it
 
Regarding your tower leg clean up... many people will make
up ground braid - short jumper straps that screw into the
tower legs over the original tower joints. There's a lot
About doing that well out of the scope of this chat, but
it's another way of reducing problems in older tower systems.
ok good idea
 
Static build up in wind might mean the antennas, duplexer or
various combinations of...  might not have a dc path (aka dc
bleed path) to ground. Static problems in dry or drier weather
conditions would be a possible indication of this problem.
One thought that did come to mind is that when one of these repeaters operate the antennas near it could be getting enough rf to excite something and generate sparks and could get more problems as the antennas move in the wind as i did read somewhere vertical fiberglass antennas sometimes break elements
 
..... but not exclusive to.    If the notch duplexers and the
antenan(s) don't go to dc/rf/station/system ground, you could
swap things around (antenna/duplexer type) to sort through the
causes.
 
Your turn...
 
skipp
 
> "Ian Wells" <[EMAIL PROTECTED]> wrote:
>  Hi guys .I have a small problem that i have been trying
> to sort out for a while now .I have 5 repeaters operating
> on one of my sites 3 vhf low band and 2 uhf band.The frequencies
> are as follows
> VHF   A-TX 70.300MHZ RX 72.800MHZ
fitted with 4 1.5 meter  by 4 inch meter tins-most likely a
notch diplexer    3db colinear ant   FM828E
> B-TX 70.5875MHZ RX 73.0875MHZ   fitted with 4 1.5 meter by 4 inch meter
> tins-most likely a notch diplexer    3db colinear  ant   FM828E
> C-TX 70.725MHZ RX 73.225MHZ      fitted with a new band pass/band reject
> possibly a varinotch     3db colinear ant    FM828E
> UHF
> D- TX 473.575 RX 478.775MHZ         fitted with mobile notch diplexer
> 6mc450s  6db colinear ant   MAXON PM150/SM4450SC
> E- TX 489.1MHZ RX 483.900MHZ      fitted with 6ld450s diplexer 6db
colinear
> ant     MAXON PM150/SM4450SC
>
> All coaxes are Heliax from antennas to Diplexers with N connectors
> Interconnecting cables between diplexers and radios  are rg223u
> A and B are a 1.5 meter apart with C in the middle
> All antennas are mounted  aprox 50 cms or more away from C or each
other .
> D and E  have a 1.5 meter between them
> ie-                                           D
>
>                                      A        C       B
>
>                                                 E
>
> I am at times having desense (ie scratch ) especially in windy weather
> occuring on repeaters B and D.It doesn't seem to affect the desense
wether
> the transmitters are txing or not .There isnt any problem of the
repeaters
> affecting each other ,they all work great just the problem of
scratch coming
> and going .A,C and E do get scratch on occasion but no where as bad
as D and
> B.D and B works great sometimes (clear with no scratch)and then
reception
> will slowly develope major scratch and then slowly clear up -possibly
> electrostatic or wind moving the antennas ?.I have been fixing loose
  bolts
> on the windmill tower to stop problems incase of tower twist and this
> affecting service.I am wondering if there are any futher sugestions .
> Thank You,
> Ian Wells,
> Kerinvale Comaudio,
>
 
 
 
 
 
 
 
 
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