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QMX Low Band - TX problem

 

I have 2 factory built QMX's, a Hi & a Low Band. They are used for DATA comms only.
Recently the Low Band radio has been acting strangely.
When it begins to TX it gives a pulse - the TX bar graph goes full for a second or so, then back to nothing, then back to transmitting as normal.
It is doing this on all bands though the worst seems to be 40M.
Power out is showing as 4.9W (The same as on the factory test paperwork)
Occasionally the TX bar graph & output "stop" at around 4 seconds into the TX cycle.?

My antenna is less than 1:1.3 across the bands - but the operation is the same when connected to a dummy load.
Changing between battery & different power supplies makes no difference.
The Hi Band radio does not have this "stutter"& works flawlessly.
I have tried different USB ports, Software, Cables, RF Chokes, Clip on Ferrites, etc.

The radio is still making FT8 contacts - it is just that it has this "stutter" at the start of the transmission & sometimes drops out part way through the TX sequence.
Anyone have a suggestion..??

Cheers
Rob
VK5ZIK
 

How are you powering it? I had an issue similar to this when the buck-boost converter that I was using to limit input voltage was silently clipping the input current (due to a bad setting on my part)

Greg, KB1UGP
 

I have tried powering it from a Talent Cell battery pack & from the same small switchmode supply that I have been using for months, as well as a 5 Amp bench supply - I don't think it is a power issue.
And since the USB cables have been swapped multipule times & USB Ports changed as well, & it still behaves the same on a Dummy Load - I don't think it is RF.
Not sure where to look next..!!

Rob VK5ZIK
 

Just wondering ... Certainly odd behavior.?

Do the PTT and TX indicator dots under the VFO letter on the LCD display also disappear when the TX stutters and/or stops?

Does the unit have the same behavior when using the hardware diagnostic TX test feature? You could hold the 'T' key for say the usual 15 seconds of an FT-8 transmission to sorta simulate. Be sure to use a dummy load.?

Depending on what you see with these two questions it might point to the PC program you are using for the DIGI operations misbehaving??

Greg


On Sat, Jul 13, 2024 at 10:18 PM, Rob VK5ZIK
<rob.at.theshed@...> wrote:
I have tried powering it from a Talent Cell battery pack & from the same small switchmode supply that I have been using for months, as well as a 5 Amp bench supply - I don't think it is a power issue.
And since the USB cables have been swapped multipule times & USB Ports changed as well, & it still behaves the same on a Dummy Load - I don't think it is RF.
Not sure where to look next..!!

Rob VK5ZIK

 

G'Day Greg
Using the Hardware TX Diagnostic Test - the TX Bargraph is a steady switch on/ switch off (The result is what I expect)
Having gotten totally confused - I have gone through this morning logically retesting everything that I can think of..

Using WSJT-X & JS8Call on both my laptop (Panasonic CF-31) & Tablet (Panasonic FZ-G1) produces the "pulse" at the start of the transmissions.. this is occurring on BOTH the Hi & Low Band QMX's
It is there regardless of which USB socket or cable I use. Sometimes the very 1st transmission is a clean switch on. (No pulse)
Occasionally - rarely, & not at repeatable intervals the LOW Band QMX does not complete a full TX cycle on the on 20M Band (Dummy Load or antenna makes no difference).
This morning I watched every Transmission (I think) for a full hour & it didn't drop out once - Frustration..!!
It has probably always done it & I haven't noticed. When it does drop out, it transmits normally for around 3 to 4 seconds then the bargraph drops to zero & no power output. The switch to Rx & next cycle are fine.

QRZ tells me I have worked 210 QSO's through 42 Countries since May - so the QMX's are working - It is just a minor glitch that I am trying to get my head around...!!
Though the occasional Tx failure after 3 - 4 seconds is obviously not right.
I have attached a short 5 sec video showing the "Pulse" at the start of the transmit sequence.

Rob
VK5ZIK
 

Well that surely is odd.?

Has anything changed recently like the firmware levels on the QMX 's or the OS's running on your older toughbooks or the versions of WSJT-X or JS8Call?

I haven't looked at the CAT logging function available on the QMX family nor am I familiar with the CAT protocol per se to be able to know what to look for exactly. Though some pattern in the CAT exchanges might be discernable based on the odd TX drop and reappearance behavior.

Hopefully others in the group might be watching this thread and could help out.

Greg




On Sun, Jul 14, 2024 at 9:29 PM, Rob VK5ZIK
<rob.at.theshed@...> wrote:
G'Day Greg
Using the Hardware TX Diagnostic Test - the TX Bargraph is a steady switch on/ switch off (The result is what I expect)
Having gotten totally confused - I have gone through this morning logically retesting everything that I can think of..

Using WSJT-X & JS8Call on both my laptop (Panasonic CF-31) & Tablet (Panasonic FZ-G1) produces the "pulse" at the start of the transmissions.. this is occurring on BOTH the Hi & Low Band QMX's
It is there regardless of which USB socket or cable I use. Sometimes the very 1st transmission is a clean switch on. (No pulse)
Occasionally - rarely, & not at repeatable in

tervals the LOW Band QMX does not complete a full TX cycle on the on 20M Band (Dummy Load or antenna makes no difference).
This morning I watched every Transmission (I think) for a full hour & it didn't drop out once - Frustration..!!
It has probably always done it & I haven't noticed. When it does drop out, it transmits normally for around 3 to 4 seconds then the bargraph drops to zero & no power output. The switch to Rx & next cycle are fine.

QRZ tells me I have worked 210 QSO's through 42 Countries since May - so the QMX's are working - It is just a minor glitch that I am trying to get my head around...!!
Though the occasional Tx failure after 3 - 4 seconds is obviously not right.
I have attached a short 5 sec video showing the "Pulse" at the start of the transmit sequence.

Rob
VK5ZIK

 

Nothing has been changed at all..!!
I have just updated to the latest Firmware - with no change.
But plugging the KX3 in - there is no "pulse" at the start of transmissions.

Rob
VK5ZIK
 

This is the setup - very basic.
The attached video shows the fault where the QMX drops out after a short (aprox 4 second) transmission.
In this video the "Pulse" when TX begins was not as obvious.
This morning it was very hard to catch the fault - this afternoon it is 2 out of 3 Transmission cycles.
Now that I am watching for it - it is happening on both the Hi & Low band QMX's. (But no sign of either the dropped Tx or Pulse on the KX3 - with same cables pc etc)
At the moment - it happens more often on the Antenna -but it occasionally happens on the Dummy Load as well.
As mentioned previously - different USB sockets, Cables, RF Cables, Power Cables & Supplies - make no difference.
Chokes etc on the antenna cable also had no effect.
The antenna is resonant - see SWR Meter in video.

Cheers
Rob VK5ZIK

 

I remember seeing something in the Operation manual about adjusting the CAT poll time for WSJT-X.

On page 60 of the latest manual version ....

Change the Poll Interval to 10 seconds, the default will be rather chatty with QMX which?
probably is not a problem, but anyway I feel more comfortable with the less frequent polling.
QMX has no capability to alter its operating frequency for example by itself, it can only do?
so at the command of WSJT-X over CAT; therefore the polling is actually redundant?
anyway.

I had to do that when testing with Fldigi, which I like to use for the ARRL frequency measuring tests. But of course, no transmitting going on there.?

If that doesn't do it, I'm out of ideas other than to check the CAT logging to see if the digi-ware is actually sending the TX start-stop-start pulse or the stop command before the time interval is up.?

Greg


On Mon, Jul 15, 2024 at 12:53 AM, Rob VK5ZIK
<rob.at.theshed@...> wrote:
Nothing has been changed at all..!!
I have just updated to the latest Firmware - with no change.
But plugging the KX3 in - there is no "pulse" at the start of transmissions.

Rob
VK5ZIK

 

Have you tried reducing the the Rise and Fall Thresholds? These control the audio level at which the digi tone is detected. I've got mine set a little lower, 60 and 50 so they work with my phone. If your audio is right on the edge this might explain things. I'd try setting the fall threshold lower to start with.

Chris, G5CTH
 

G'Day Chris - I will have a fiddle with the Rise & Fall Thresholds.
BUT as I mentioned before, these are Factory Assembled QMX's & QRZ tells me I have successfully worked 210 QSO's through 42 Countries since May....
?
So I don't understand why they suddenly need adjustments..
Absolutely nothing has changed in the setup, not even the location of the radio on the desk.
?
Cheers
Rob VK5ZIK

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