The bandwidth of an AM receiver might be 10khz, the QMX strips out all but 3.2khz of that AM signal.
While it is harder to tune in with the QMX, if there are interfering signals within the 10khz AM signal
then this can often be filtered out using the QMX receiver.? What's more, you can choose to use either
the upper sideband or the lower sideband of that AM signal, whichever has less interference.
?
It should be possible to add normal AM reception to the QMX through a firmware update,?
but that would be a very low priority for a rig meant to be used on the ham bands.
Especially since using the QMX as an SSB receiver often gives better results.
?
Jerry, KE7ER
?
?
On Mon, Mar 24, 2025 at 03:38 AM, Chris wrote:
The current QMX SSB receiver can receive AM because what is transmitted is the two sidebands and a carrier but it's not receiving it as AM, it's receiving as SSB using one sideband of the AM signal and ignoring the other sideband and the carrier.? You don't get the advantages of true AM reception where precise tuning is not required, and you have thrown away half of the data.
?
Try it with a rig that can receive SSB and true AM on a broadcast AM signal.? You will see that the AM signal can be received as SSB but you need precise tuning to get the correct tone, with AN you don't need precise tuning and the signal to noise is a little better.
?
Chris, G5CTH
|
Nate,
?
When Allison says a max of 16 volts, she means the power supply into the rig.
Transmitting on 80m with the QMX from a 12v supply into a 50 ohm dummy load can cause
peak voltages of more than 60 volts from drain to ground at those BS170's.?
And 60v is the absolute max listed in the BS170 datasheet.
?
In addition to reading the datasheet for the FET's, you also need to know how the circuit works.
That is not a trivial task, unless like Allison you have spent a career doing this stuff.
Here's a tutorial on a Voltage Mode Class D push-pull amp such as used on the QMX:
?
?
Why such high voltages?
As described in that tutorial, the action of transformer T501 causes twice the power supply voltage to appear
across each BS170 when it is not conducting.? In addition, the LPF in the QMX blocks
the undesired harmonic currents from going out to the load, which raises voltages further.
?
For those wishing to see what's going on, I'd recommend using
the LTSpice simulator on a model of the QMX final.? Such a model can be found
in the left-most of the four simulations found in this file:
The discussion is in this thread:??
?
Jerry, KE7ER
?
?
?
On Mon, Mar 24, 2025 at 05:20 AM, Nate Reik wrote:
On Sun, Apr 25, 2021 at 10:53 AM, ajparent1/kb1gmx wrote:
There is some magical thinking with regard to RD15hhf parts.
RTFM, in this case, the data sheet.
First its a 16V max part.
Can someone explain this? I'm trying to understand maximum values of RF transistors...and the RD16HHF1 datasheets I see don't say 16v anywhere. I see 20v and 50v ratings...and I see things about rules of thumb elsewhere...but how do I determine from the datasheet of an RF transistor what the maximum DC supply voltage is?
?
Thanks for any help with my learning!?
?
-Nate
N8BTR
|
Re: QMX+ Mono Audio Output
Paul,
?Okay thanks!
?
Dave
W6MQI
|
I'd appreciate some pointers to guidance on RF circuit design, especially power amplifiers.? Some sort of text book maybe.
?
Chris, G5CTH
|
Re: QMX+ Mono Audio Output
Dave,
I have an old set of Radio Shack communications headphones that are mono. I use a mono to stereo adapter plug on it and it works fine. It's similar to this one:
?
--
73, Dan - W2DLC
|
WSJT-X has moved on to 2.8.0 now.? The 'improved' versions are 'authorised' as they are made by one of the developers as a way to trial additional features, some of which are useful.? That one was sent privately to fix a long standing bug that I'd been pestering about since last October.? There's a lot on the web about them.
?
Chris, G5CTH
|
Thanks again Hans for the great work on this radio and firmware! in addition to many US and CA contacts from my QTH in Minnesota, I’ve made my first ever QRP DX contacts. Madeira island on the first firmware version the first day and yesterday afternoon to Switzerland! ?Both on 20m using a 1/2 wave dipole in my attic. These were big stations with big ears but they gave good signal reports.?
I haven’t used my main radio all week!?
KF0OUH
?
|
Ahhh, so thus 50v divided by 3 or 4.... Giving 12.5-16.6V. Got it.?
So it would be OK for 20v IF you had a perfect output load matched to the transistor? Makes sense. Thanks, Gary!?
?
-Nate
N8BTR?
|
On 24/03/2025 11:42, Martin DK3UW via groups.io wrote: so that is not the original WSJTX ? Martin, It is a modified version, (improved in some ways?). Try it if you wish although I would think it best to use the 2.7.0 version if it does what you want. Hamlib is here 73 Alan G4ZFQ
|
Re: SSB Calibration blown finals
Richard, I did this in QDXs with a Wakefield heatsink I drilled and tapped.?
?
?
-Nate?
N8BTR
|
The RF voltage swing on the drain of the part is nominally twice the DC supply voltage but could go higher with higher load impedances. 3-4 times the DC voltage for the drain breakdown rating is a good margin of safety.
Gary
W9TD
|
Re: Using Retevis HK-008 speaker microphone with QMX for SSB
?I’m using this mic and can confirm the wire color mapping is the same as in the video. Same jack configuration as the (tr)uSDX which I have used too. The speaker is loud but emphasizes the high frequencies including the static so I've found it fatiguing to listen too for a while vs using earbuds. It may be better when outside and you want a speaker without extra gear.
?
Go for the firmware, it works great!?
|
I did an outdoor test of the portable setup today with the aim of going up a local hill later.? As I chased an Italian POTA and 2E0XGO/P on G/LD-036, Melbreak, without much effort on my part spending time and fuel for a further test seemed pointless.? I hope to do a proper activation tomorrow.
?
As I don't do CW? I risked installing the Beta SSB version so that I could actually test the QMX properly.? Absolutely delighted with what I could hear this morning and very much looking forward to its first activation.? Very many thanks Hans - more coffee on the way shortly.
73,
Rod
?
|
On Sun, Apr 25, 2021 at 10:53 AM, ajparent1/kb1gmx wrote:
There is some magical thinking with regard to RD15hhf parts.
RTFM, in this case, the data sheet.
First its a 16V max part.
Can someone explain this? I'm trying to understand maximum values of RF transistors...and the RD16HHF1 datasheets I see don't say 16v anywhere. I see 20v and 50v ratings...and I see things about rules of thumb elsewhere...but how do I determine from the datasheet of an RF transistor what the maximum DC supply voltage is?
?
Thanks for any help with my learning!?
?
-Nate
N8BTR
|
On Mon, Mar 24, 2025 at 11:04 AM, Chris wrote:
WSJT-X v2.8.0 20250314 Improved Plus.
so that is not the original WSJTX ? If I am right my verson of WSJTX is 2.7.0 and I could not find, where to see the Hamlib version. I just wonder, if it would not be best tu uninstall what I have and download again.
?
--
Martin
DK3UW
|
Re: QMX Time Synchronisation Bug
Hi Carol
?
Thanks for this observation - I have just uploaded the latest SSB firmware, and done a hardware reset. I was wondering why the QMX+ RTC wasn't updating. Setting "software" mode cured it - update manual please, Hans.
?
773
Tony, G3OVH
|
Re: #qmx #SSB Firmware beta 1_01_003 release
#qmx
#ssb
On Mon, Mar 24, 2025 at 02:31 AM, Chris wrote:
What is the power output during normal CW or digital transmit or Transmit in the diagnostics?
I just did a quick test at 12.0v using Transmit in the diagnostics, all bands are around 5w except 60m this was 6.4w.
?
Just to emphasise this is just an observation as some people were have problems with finals whilst carrying out the calibration.
?
?
|
Re: Internal mic seems to be working?
#qmx
#ssb
On Sat, Mar 22, 2025 at 01:27 AM, Yoon KM6KJI wrote:
Anyone tried the internal mic to make a real contact?
My first SSB contact using the devices was over the internal mic, and using my left paddle to "key" PTT.?? It works, but was less than ideal. Currently I am using SSB over the USB audio and running my mic and headphone through my computer while I wait for my digikey order to come in.
|
Re: SSB Calibration blown finals
On Sun, Mar 23, 2025 at 11:15 PM, mux_folder2001 wrote:
What is the highest frequency you are using the TN0110s on?
|
Re: shorted PA on TX, dead SMPSU?
@Evan, thanks, I tested this as above, got 6.6k ohm gnd to Vcc and 2.3k ohm gnd to Vdd.?
?
@Stan I've ordered new SMPSU boards and I'll report back when I've tested as per your message
?
Thanks to all for your help
Dan
?
|
W6MQI
Daniel Conklin
Gary W9TD