[pskmail] Re: QRM ??

  • From: Franz Rohrauer <franz.rohrauer@xxxxxx>
  • To: pskmail@xxxxxxxxxxxxx
  • Date: Fri, 05 Jun 2015 00:51:09 +0200

Hi, Juergen,

I use a very simple trick to reduce the problem with this qrm (it's
timing seems to me, it's a winlink-station):

I changed fldigi's audio-frequency (audio-subcarrier) up to 2500 Hz and
reduced radio-frequency to 10145.5 kHz (10145.5 kHz + 2.5 kHz = 10148
kHz on USB-mode). On my good old IC735 I can activate "BPT" (Band Pass
Tuning) by moving the center frequency of an IF-Filter (details see
document http://www.radiomanual.info/schemi/IC735_user.pdf , page 38,
chapter 6-10-1). So I can limit audio-passband between 2200 and 2800 Hz.
Audio-carrier of 2500 Hz (rf-carrier 10148 kHz) passes, qrm as you
describe moves up to 3000 Hz and is eliminated by the IF-filters.

Without the possibility of Band Pass Tuning ("BPT") on rf of 10145.5 kHz
the receiving channel on USB is "open" between 10146.0 and 10148.5 kHz.
I tested this bandwidth by switching off BPT, qrm was very low. Much
better than by using 10147 kHz.

73 de

Franz, oe5rtl

Am 2015-06-03 um 18:17 schrieb Juergen:

Hi,
lately I have a lot of QRM during pskmail operation. It's nearly
impossible to finish a data transfer and so "Abort" is mostly the end.
I've looked around a bit in the Internet and found that Robust Packet (
http://robust-packet.net/ ) uses the 10.147,30 MHz USB for it's
transmissions. Is ist possible this caused the QRM, has anybody made
similar expierences ?
I've attached a fldigi screenshot when the transmission took place.
To identify the signal I've looked about a Robust Packet sound file
example, but unfortunately I found nothing.

73
Juergen
DL8JF

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