[pskmail] Re: QRM ??

  • From: Juergen <dl8jf@xxxxxxxxxxxx>
  • To: pskmail@xxxxxxxxxxxxx
  • Date: Fri, 05 Jun 2015 14:26:05 +0200

Hi Franz,
that's a good tip, thank you.
I've tried it and changed: Configure/Misc/Pskmail/Carrier frequency (Hz) in fldigi from 1000 Hz to 2500 Hz.
Then I changed the radio frequency from 10147.00 kHz to 10145.50 kHz.
My ICOM IC-706MKIIG has a similiar function for band pass tuning.
When I turn the "Shift" knob, it moves the IF frequency to an upper or lower limit. So, receiving works quite well now.
After the start of jpskmail 1.8.3 the receiving offset frequency in fldigi is 2500 Hz, but when transmitting starts the offset changed back to 1000 Hz .This gives a resulting transmit frequency of 10146.50 kHz. I then changed the "Offset (Hz)" in jpskmail "Preferences/Rig" from 1000 Hz to 2500 Hz, restarted it, but it has no effect. The transmit offset frequency remains at 1000 Hz.
Do I have forget something or do I have understood something in your explanation wrong ?


On 06/05/2015 12:51 AM, Franz Rohrauer wrote:

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

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