Audio Frequency choice. #QSO_practices


mbigos@...
 

Hi -

I have been using FT8 for 4 months on 40 & 20 meters and notice that signals bunch between 1 kHz and 2 to 2.5 kHz. Can someone explain to me (or point me at some good write-ups) as to why this happens? Is there some magic going on that I am missing, or is it just herd instinct? I generally try to use 800-950 Hz, and get reasonable results with a QRP rig and compromise antenna. Thanks in advance, 73.

Marty
KN6OKN


mike
 

Simples, you are transmitting an audio tome on an SSB transmitter, the
bandwidth of the SSB transmitter is roughly 300Hz to 3Khz, anything outside
that will not be transmitted or severely attenuated. Your receiver has an
audio response to fit with the SSB TX response.. OK ?

On 24 Sep 2021 at 15:12, mbigos@sonic.net wrote:

Subject: [WSJTX] Audio Frequency choice. #QSO_practices
To: main@WSJTX.groups.io
From: mbigos@sonic.net
Date sent: Fri, 24 Sep 2021 15:12:10 -0700
Send reply to: main@WSJTX.groups.io

Hi -

I have been using FT8 for 4 months on 40 & 20 meters and notice that signals
bunch between 1 kHz and 2 to 2.5 kHz. Can someone explain to me (or point me
at some good write-ups) as to why this happens? Is there some magic going on
that I am missing, or is it just herd instinct? I generally try to use
800-950 Hz, and get reasonable results with a QRP rig and compromise antenna.
Thanks in advance, 73.

Marty
KN6OKN


Bill Somerville
 

On 24/09/2021 23:12, mbigos@sonic.net wrote:
Hi -

I have been using FT8 for 4 months on 40 & 20 meters and notice that signals bunch between 1 kHz and 2 to 2.5 kHz. Can someone explain to me (or point me at some good write-ups) as to why this happens? Is there some magic going on that I am missing, or is it just herd instinct? I generally try to use 800-950 Hz, and get reasonable results with a QRP rig and compromise antenna. Thanks in advance, 73.

Marty
KN6OKN
Hi Marty,

one reason may be that users who do not have CAT control of their rigs are following our advice to use Tx audio offsets above 1500 Hz. This ensures that any unwanted audio harmonics are greatly attenuated by the rig's Tx IF filter. Of course they can elect to tune their VFO dial down 1 or 1.5 kHz if they wish to get to those lower frequencies.

73
Bill
G4WJS.


Michael Black
 

I'm guessing you are probably using Data/Pkt mode in WSJT-X.
Many rigs have limited bandwidth.  Some can adjust that bandwidth.

What rig do you have?
What are your bandwidth settings?

Mike W9MDB

Hi Marty,

one reason may be that users who do not have CAT control of their rigs
are following our advice to use Tx audio offsets above 1500 Hz. This
ensures that any unwanted audio harmonics are greatly attenuated by the
rig's Tx IF filter. Of course they can elect to tune their VFO dial down
1 or 1.5 kHz if they wish to get to those lower frequencies.


73

Bill
G4WJS.






Gene Horr
 

1)  A lot of DX stations seem to prefer below 1KHz.  Also Fox/Hound mode (also usually DX) requires them to stay below 1KHz.  So some people try and keep that free for the DX stations.
2) As mentioned a lot of radios don't work well close to the band edges.  If you stay away from the edges you don't have to worry about that.  Your radio may work close to the edge but by doing so you are cutting out a lot of contacts from people who's radio doesn't work well there.
3) If you are trying to work a DX station it helps to lower the base frequency by 300-500Hz. This now means that the top end of the FT8 band is no longer available.

All of these combine to make it more likely that there will be fewer stations on the high and low ends.

Nothing wrong with your choice and I can see where it will help you make contacts by lowering the competition.  I can't imagine any rational person complaining about a QRP station operating there.  1500 Watts?  That's a little different.  Of course this is ham radio.  An assumption of rationality may be a bit naive.  

Gene
NG1H


Reino Talarmo
 

Hi Gene,

 

Just a snapshot here in Finland 24 h on 20m band almost 150 000 messages.

 

High end is limited by my rig and wsjt-x waterfall setting. I would say quite a flat distribution.

 

73, Reino OH3mA

 

1)  A lot of DX stations seem to prefer below 1KHz.  Also Fox/Hound mode (also usually DX) requires them to stay below 1KHz.  So some people try and keep that free for the DX stations.
2) As mentioned a lot of radios don't work well close to the band edges.  If you stay away from the edges you don't have to worry about that.  Your radio may work close to the edge but by doing so you are cutting out a lot of contacts from people who's radio doesn't work well there.
3) If you are trying to work a DX station it helps to lower the base frequency by 300-500Hz. This now means that the top end of the FT8 band is no longer available.

All of these combine to make it more likely that there will be fewer stations on the high and low ends.

Nothing wrong with your choice and I can see where it will help you make contacts by lowering the competition.  I can't imagine any rational person complaining about a QRP station operating there.  1500 Watts?  That's a little different.  Of course this is ham radio.  An assumption of rationality may be a bit naive.  


Kermit Lehman
 

I have very good luck calling CQ below 500 Hz and above 2500 Hz when bands, especially 20m and 40m, are congested.  About half of those calling me are in the central  part of the band and operating split.


It seems they can hear out to the ends of the bands but not don't transmit there for whatever reason.


The interesting graph below looks correct to me.


73,

Ken, AB1J


-----Original Message-----
From: Reino Talarmo <reino.talarmo@...>
To: main@WSJTX.groups.io
Sent: Sat, Sep 25, 2021 5:40 pm
Subject: Re: [WSJTX] Audio Frequency choice. #QSO_practices

Hi Gene,
 
Just a snapshot here in Finland 24 h on 20m band almost 150 000 messages.
 
High end is limited by my rig and wsjt-x waterfall setting. I would say quite a flat distribution.
 
73, Reino OH3mA
 
1)  A lot of DX stations seem to prefer below 1KHz.  Also Fox/Hound mode (also usually DX) requires them to stay below 1KHz.  So some people try and keep that free for the DX stations.
2) As mentioned a lot of radios don't work well close to the band edges.  If you stay away from the edges you don't have to worry about that.  Your radio may work close to the edge but by doing so you are cutting out a lot of contacts from people who's radio doesn't work well there.
3) If you are trying to work a DX station it helps to lower the base frequency by 300-500Hz. This now means that the top end of the FT8 band is no longer available.

All of these combine to make it more likely that there will be fewer stations on the high and low ends.

Nothing wrong with your choice and I can see where it will help you make contacts by lowering the competition.  I can't imagine any rational person complaining about a QRP station operating there.  1500 Watts?  That's a little different.  Of course this is ham radio.  An assumption of rationality may be a bit naive.