locked Transmit products - What is this ? #WSJTX_config


Tim
 

Hi all,

I've noticed a few stations with what appears to be transmit products. I've seen this on both local and DX and I'm wondering if there is a chief cause of this.

A local station, only 900 metres away!, produces products like this and we'd like to find the issue.

Even at 1/2 power and no AGC action we see these products. So any pointers appreciated.

see image below.

thanks

Tim

-- 
VK2XAX : QF56if : ITU59 : CQ30 : BMARC : WIA


johnsherry57
 

I have issues with some stations a few miles away. I was running with agc off.
A local ham with years of experience said I should run with agc on.
Problem solved. 

John GM0AZC 

On Fri, 30 Jul 2021, 07:39 Tim, <VK2XAX@...> wrote:

Hi all,

I've noticed a few stations with what appears to be transmit products. I've seen this on both local and DX and I'm wondering if there is a chief cause of this.

A local station, only 900 metres away!, produces products like this and we'd like to find the issue.

Even at 1/2 power and no AGC action we see these products. So any pointers appreciated.

see image below.

thanks

Tim

-- 
VK2XAX : QF56if : ITU59 : CQ30 : BMARC : WIA




Tim
 

Hi John,

OK, I wasn't clear in my original post about AGC.

The AGC action I'm talking about is for TX. i.e. TX audio is wound back until there is not AGC indication on TX.

These artefacts happen with two different radios on TX from the local guy.

This has nothing to do with RX AGC since it is present on some weak signals too.

regards

Tim


--
VK2XAX : QF56if : ITU59 : CQ30 : BMARC : WIA


Tim
 

A correction...

I meant to say ALC instead of AGC :)

Its been one of those days!

thanks

Tim


On 30/7/21 4:58 pm, Tim via groups.io wrote:
Hi John,

OK, I wasn't clear in my original post about AGC.

The AGC action I'm talking about is for TX. i.e. TX audio is wound back until there is not AGC indication on TX.

These artefacts happen with two different radios on TX from the local guy.

This has nothing to do with RX AGC since it is present on some weak signals too.

regards

Tim





-- 
VK2XAX : QF56if : ITU59 : CQ30 : BMARC : WIA


Reino Talarmo
 

Hi Tim,

This is a typical case where audio frequency is below, say 1500 Hz, and audio chain is not linear for some reason. Un-linearity could be at any part of the chain from WSJT-X digital audio generation to transmitter mixer.
WSJT-X generates perfect digital signal from +1 to -1 ie. full scale, but there may have digital gain in Windows. See pinned mail #13860 for proper Windows 10 settings.
Another point could be any analog audio part overdriving after D/A in audio codec. The codec may be in PC, external sound card or sound card in rig. In some rigs excessive ALC could be an indication of that overdriving.
The best correction is to use split in WSJT-X either Rig or Fake It. That requires functioning CAT. Another solution is to use audio frequencies above 1500 Hz.

Based on that waterfall I can say that the un-linearity is symmetric as the second harmonic (three times the audio frequency) is clearly present. As the harmonics is present also at a lower power, then it is generated in some audio part. If WSJT-X Pwr slider changes harmonic level sharply, then reason can be in digital gain in Windows.

Short advice Use Split!

73, Reino OH3mA

>A local station, only 900 metres away!, produces products like this and we'd like to find the issue.

>Even at 1/2 power and no AGC action we see these products. So any pointers appreciated.


Alan G4ZFQ
 

I have issues with some stations a few miles away. I was running with agc off.
A local ham with years of experience said I should run with agc on.
John

As a non-local with years of experience I reckon that with a modern RX with suitable attenuation or RF gain adjustments there will be sufficient dynamic range.
AGC is not required unless your neighbour is an amateur. Even then it will probably make little difference, AGC or overload will desense the RX.

If you do use AGC then weak signals could be suppressed unnecessarily depending on the values of excess RF gain and the efficiency of your antenna.
After saying all that you might find it difficult to notice any difference without something as a comparison. Do what you feel is right:-)

73 Alan G4ZFQ


ve3ki
 

That appears to be the third harmonic of the signal just below 500 Hz on the waterfall. If the other station's signal is very strong, the harmonic signal that you see might have been generated  by overdriving an audio stage in the receive audio chain. A way to tell is to slowly back off the RF gain on the receiver - if the harmonics disappear much faster than the fundamental, then the harmonics are being generated in the receiver/receive sound card chain. If the harmonics decrease in strength at the same rate as the fundamental does, then they are being generated at the transmitter.

73,
Rich VE3KI


On Fri, Jul 30, 2021 at 02:39 AM, Tim wrote:

Hi all,

I've noticed a few stations with what appears to be transmit products. I've seen this on both local and DX and I'm wondering if there is a chief cause of this.

A local station, only 900 metres away!, produces products like this and we'd like to find the issue.

Even at 1/2 power and no AGC action we see these products. So any pointers appreciated.

see image below.

thanks

Tim

-- 
VK2XAX : QF56if : ITU59 : CQ30 : BMARC : WIA


Ray
 

I a


Ray
 

I agree with that procedure Rich, the WSJT- waterfall is not calibrated so it is difficult to determine signal quality with the waterfall,

Ray W8LYJ


Ray
 

As discussed extensively on the K4 email list, it takes a +60,70 db signal to overload a receiver. Only close by transmitters will cause overload. Many receivers today have an overload indicator to show when receiver is overloaded. 

Ray W8LYJ


Alan G4ZFQ
 

I've noticed a few stations with what appears to be transmit
products. I've seen this on both local and DX and I'm wondering if
there is a chief cause of this.
Tim,

Going back to your first post. What do you mean? I see some signals with maybe 12 tones between 1400-1500Hz in your yellow box. Is that what you are asking?

73 Alan G4ZFQ


Andrea Tommasi
 

Hello,
to understand if the harmonic signal is generated by the TX or the RX I think the easy way is to shift the reception by 100 Hz and if the harmonic signal moves by 300 Hz from the useful signal the harmonic is by the receiver, if instead it remains at the same distance from the useful signal the harmonic is generated by the TX station.
IE: the useful signal 500 Hz and harmonic 1500Hz on standard frequency, tune RX -100 Hz useful signal become 600 Hz, if the harmonic goes to 1800 Hz it is generated by the RX if instead it is at 1600Hz it is generated by TX, assuming that both devices are exactly in frequency.
On my 2 m RTX TS711E most case of harmonics are generated by my RX section.

73 de IK4IDP
Andrea
sry for google translation.

Il 30/07/2021 15:21, Ray ha scritto:
I agree with that procedure Rich, the WSJT- waterfall is not calibrated so it is difficult to determine signal quality with the waterfall,

Ray W8LYJ




Michael Black
 

It's 8 tones and is the 3rd harmonic of the signal at around 440.

440*3=1320 is where the harmonic should be -- which indicates somebody's frequency calibration is off by a bit -- 15-20Hz -- typically on older rigs.
The harmonic is around 1370 so the difference from 1320 50Hz/3 = 16.7Hz.
I've seen this quite a few times with all the operators I've helped.  You can either calibrate the rig or use WSJT-X's calibration to correct it.

The harmonic is cause by clipping the signal -- either at the transmitter or receiver.  Usually it's the transmitter but with somebody 900 meters away could be the receiver too.

Mike W9MDB






On Friday, July 30, 2021, 08:36:02 AM CDT, Alan G4ZFQ <alan4alan@...> wrote:


>    I've noticed a few stations with what appears to be transmit
>    products. I've seen this on both local and DX and I'm wondering if
>    there is a chief cause of this.

Tim,


Going back to your first post. What do you mean? I see some signals with
maybe 12 tones between 1400-1500Hz in your yellow box. Is that what you
are asking?

73 Alan G4ZFQ





Alan G4ZFQ
 

It's 8 tones and is the 3rd harmonic of the signal at around 440.
Mike,

Right! Thanks, I'd not connected the two.

73 Alan G4ZFQ


 

If it is overdriving in the RX chain, you would expect to see similar artefacts for the other signals of similar strength. Judging by the colours there are several signals of similar strength in other time slots.

 

73 Phil GM3ZZA

 

Sent from Mail for Windows 10

 

From: ve3ki
Sent: 30 July 2021 13:23
To: main@WSJTX.groups.io
Subject: Re: [WSJTX] Transmit products - What is this ? #WSJTX_config

 

That appears to be the third harmonic of the signal just below 500 Hz on the waterfall. If the other station's signal is very strong, the harmonic signal that you see might have been generated  by overdriving an audio stage in the receive audio chain. A way to tell is to slowly back off the RF gain on the receiver - if the harmonics disappear much faster than the fundamental, then the harmonics are being generated in the receiver/receive sound card chain. If the harmonics decrease in strength at the same rate as the fundamental does, then they are being generated at the transmitter.

73,
Rich VE3KI


On Fri, Jul 30, 2021 at 02:39 AM, Tim wrote:

Hi all,

I've noticed a few stations with what appears to be transmit products. I've seen this on both local and DX and I'm wondering if there is a chief cause of this.

A local station, only 900 metres away!, produces products like this and we'd like to find the issue.

Even at 1/2 power and no AGC action we see these products. So any pointers appreciated.

see image below.

thanks

Tim

-- 
VK2XAX : QF56if : ITU59 : CQ30 : BMARC : WIA

 


--
73 Phil GM3ZZA


Michael Black
 

You can't tell signal strength easily from the waterfall colors....

Adjusting your receive frequency as recommended will show you if it's you or your friend.

Mike W9MDB


On Friday, July 30, 2021, 09:09:02 AM CDT, Philip Rose via groups.io <gm3zza@...> wrote:


If it is overdriving in the RX chain, you would expect to see similar artefacts for the other signals of similar strength. Judging by the colours there are several signals of similar strength in other time slots.

 

73 Phil GM3ZZA

 

Sent from Mail for Windows 10

 

From: ve3ki
Sent: 30 July 2021 13:23
To: main@WSJTX.groups.io
Subject: Re: [WSJTX] Transmit products - What is this ? #WSJTX_config

 

That appears to be the third harmonic of the signal just below 500 Hz on the waterfall. If the other station's signal is very strong, the harmonic signal that you see might have been generated  by overdriving an audio stage in the receive audio chain. A way to tell is to slowly back off the RF gain on the receiver - if the harmonics disappear much faster than the fundamental, then the harmonics are being generated in the receiver/receive sound card chain. If the harmonics decrease in strength at the same rate as the fundamental does, then they are being generated at the transmitter.

73,
Rich VE3KI


On Fri, Jul 30, 2021 at 02:39 AM, Tim wrote:

Hi all,

I've noticed a few stations with what appears to be transmit products. I've seen this on both local and DX and I'm wondering if there is a chief cause of this.

A local station, only 900 metres away!, produces products like this and we'd like to find the issue.

Even at 1/2 power and no AGC action we see these products. So any pointers appreciated.

see image below.

thanks

Tim

-- 
VK2XAX : QF56if : ITU59 : CQ30 : BMARC : WIA

 


--
73 Phil GM3ZZA