[OZAPRS] Fwd: [VK2-APRS] APRS interference issue

[Colin Matten]

We found the APRS 828 has almost no filtering of harmonics. If we can
reduce the 290.350MHz harmonic, it may reduce the intermod interference.

However, I believe the old rule is if you can mathematically workout the
intermod from the services at the site, you will be hard pressed to fix
it without changing frequency on one of the service.
 
Regards

Colin VK2KCM


-----Original Message-----
From: ozaprs-bounces at aprs.net.au [mailto:ozaprs-bounces at aprs.net.au] On
Behalf Of Grant (VK5ZWI)
Sent: Friday, 22 August 2008 9:20 AM
To: Australian APRS Users
Subject: RE: [OZAPRS] Fwd: [VK2-APRS] APRS interference issue

That may be almost incurable. We had it here in Adelaide years ago and
had to put it down to rusty bolts in the tower - as it came and went
when we shook it (it was a 120ft free standing job).

You will be very hard pressed to control it without one or other of the
services changing frequency as anything non-linear on the site that can
act as a diode can produce the mixing effect and have it reradiate
around the site.  (I am assuming at this point that your WICEN repeater,
UHF repeater and APRS digipeater are all colocated?)

The case we had years ago was 147.575 mixing with 147.000 to produce
146.425 - only 25KHz above the repeater input. We ended up moving the
packet to 144.925 to get away from the problem.  Your mix is a little
more complicated but being only first and second order can still be
fairly easy to produce.

Regards,
Grant VK5ZWI


-----Original Message-----
From: ozaprs-bounces at aprs.net.au [mailto:ozaprs-bounces at aprs.net.au]On
Behalf Of David Hardy
Sent: Thursday, 21 August 2008 9:13 AM
To: ozaprs at aprs.net.au; VK2-APRS at yahoogroups.com
Subject: RE: [OZAPRS] Fwd: [VK2-APRS] APRS interference issue




 All,

The cause of the issue has been found. It is a local intermod of our UHF
repeater 438.075 - (2 x APRS) 290.350 = 147.725 our WICEN repeater
input.
Now the task is to find out where it is coming from!


Dave


(Receivers and Managers Appointed) (Administrators Appointed

-----Original Message-----
From: ozaprs-bounces at aprs.net.au [mailto:ozaprs-bounces at aprs.net.au] On
Behalf Of Damien Gardner Jnr
Sent: Wednesday, 20 August 2008 4:59 PM
To: Australian APRS Users
Subject: [OZAPRS] Fwd: [VK2-APRS] APRS interference issue

Forwarded to ozaprs, as I dont' think anyone uses the vk2-aprs list ;)

Begin forwarded message:

> From: "vk2ydh" <vk2ydh at terrigal.net.au>
> Date: 20 August 2008 4:54:17 PM
> To: <VK2-APRS at yahoogroups.com>
> Subject: [VK2-APRS] APRS interference issue
> Reply-To: VK2-APRS at yahoogroups.com
>
> Hi,
>
>  I'm from the Central Coast ARC and we are getting APRS packets on our

> WICEN VHF Repeater 147.125 TX and 147.725 MHz RX at Somersby.
>
>  The packets are mainly 07:45 - 08:15 and 4:45 - 5:15PM and 
> intermittent through the day and night.
>
>  We are receiving a strong signal at Somersby on 147.725 MHz (repeater

> input) it can't be heard at Kanwal and we are attempting to track down

> the source.
>
>  Can people  check to make sure they are not inavertantly txing on out

> repeater input?
>
>  Regards,
>
>  Dave Hardy
>  vk2jdh
>
>
>  Sample packet dump of rx.
>
>  Mon Aug 18 08:13:01 2008 - 4700 recv:
>  KISS: Port 0 Data
>  AX25: VK2INT-5->APU25N v VK2RAG-1* INETNC UI pid=Text  0000
> }VK2RBX-1>APNU19,TCPIP,VK2INT-5*:!3412.65SS14215.84E#PHG5330/W2
>  0040  APRS Digi - Mildura - (2).
>
> [Non-text portions of this message have been removed]
>
>
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