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LPF Sweep for QDX and QMX #qdx #qmx

 

Hans,

A feature request for both the QDX and QMX:? Adding a low-pass filter sweep.? This would be especially helpful on the QMX, as using the QCX LPF tweaking method is difficult.? It could also help in the LPF switching diagnostics.

73
Evan
AC9TU
 

Hello Evan

It's a difficult thing. There's no BPF bypass and no way to separate the response of the BPF from that of the LPF.?

On QMX you could sort of do it crudely by measuring power output power but still it would mix up LPF attenuation with impedance variation.?

Open to any ideas here?

73 Hans G0UPL


On Fri, Sep 22, 2023, 4:20 PM Evan Hand <elhandjr@...> wrote:
Hans,

A feature request for both the QDX and QMX:? Adding a low-pass filter sweep.? This would be especially helpful on the QMX, as using the QCX LPF tweaking method is difficult.? It could also help in the LPF switching diagnostics.

73
Evan
AC9TU

 

Hans:
I think it could be done if you run the PAs at low voltage (commanded through Q507) and sweep the frequency while reading the forward power through T507 with the future SWR firmware.? Obviously must be at low power to protect the PAs (BS170s) and with a 50 ohm dummy load.
If this would work it should be fairly low on your firmware upgrades.
Chris?
 

Chris, that is one possible way to do a measurement if the detector response can be sufficiently linearized in post-ADC computation.

One downside is that the amplifier's output impedance and the load impedance are interdependent, and the filter's input impedance can vary depending on the frequency. So, the measurement is a good one for real-life output vs freq at any particular operating power, but it is not necessarily a fair measurement method for the LPF's frequency response. Measuring the latter in vivo is difficult, as Hans said.
 

Hello Hans,

Thank you for the response.

For the current QMX, using the unused 0 BPF selection on IC402 might be possible.? That could be set up with jumpers to bypass the BPF.? That does take up one of the BPF selections.? Is it possible to factor in the BPF response based on the assumption that the lower half of the frequency response is the same as the upper half?? That could be factored into the measurements.? I am unsure if that would be accurate enough for adjustments.

It was just a suggestion and at a much lower priority than anything on your current list.

73
Evan
AC9TU
 

Hi Evan, Chris, Ryuji

I can quite easily set up a sweep in QMX based on power output measurement. Everything interacts with everything. I don't think you can make too many assumptions about symmetric BPF sweep etc. So it'll be just a "for what it's worth" indicative kind of a sweep. Best we can do...

FYI yesterday I got Power and SWR working nicely on my QMX. I added it to the diagnostics screen in the terminal. And also the LCD during transmit. It shows both power out and SWR in the 3 LCD characters between the mode indicator and battery voltage icon. Power is 0 to 6W full scale deflection whereas SWR shows 1.0 to 4.0 with each "bar" worth 0.2. I also added a configurable SWR protection feature.

73 Hans G0UPL


On Fri, Sep 22, 2023, 8:06 PM Evan Hand <elhandjr@...> wrote:
Hello Hans,

Thank you for the response.

For the current QMX, using the unused 0 BPF selection on IC402 might be possible.? That could be set up with jumpers to bypass the BPF.? That does take up one of the BPF selections.? Is it possible to factor in the BPF response based on the assumption that the lower half of the frequency response is the same as the upper half?? That could be factored into the measurements.? I am unsure if that would be accurate enough for adjustments.

It was just a suggestion and at a much lower priority than anything on your current list.

73
Evan
AC9TU

 

Great,
Sent you more caffeine.
 

Relative performance would be useful, as long as typical performance is added to the Assembly Instructions or Operating Manual.? It would show obvious mistakes:
1) PIN diodes oriented correctly
2) Correct location of inductors
3) Miss wound Inductors - If there is sufficient precision
4) Correct LPF capacitors
5) Issues with T501, T507 etc.
6) Solder joints in the output chain.
Note the QMX is so compact it is difficult to verify components after assembly, so any self debugging is useful.?
 

Hello Chris

I'll give it a try and we can see how good it is. Currently the RF sweeps operate the receiver, inject a signal on the Clk2 output of the 5351 at a 1kHz offset, and then measure the 1kHz audio. So some small changes are required in order to instead?operate the transmitter, and use the SWR bridge to measure power output. All the plotting can be the same.?

73 Hans G0UPL



On Sun, Sep 24, 2023 at 4:58?PM Chris KB1NLW via <chrisrey1=[email protected]> wrote:
Relative performance would be useful, as long as typical performance is added to the Assembly Instructions or Operating Manual.? It would show obvious mistakes:
1) PIN diodes oriented correctly
2) Correct location of inductors
3) Miss wound Inductors - If there is sufficient precision
4) Correct LPF capacitors
5) Issues with T501, T507 etc.
6) Solder joints in the output chain.
Note the QMX is so compact it is difficult to verify components after assembly, so any self debugging is useful.?

 

On Sun, Sep 24, 2023 at 09:58 AM, Chris KB1NLW wrote:

Note the QMX is so compact it is difficult to verify components after assembly, so any self debugging is useful.

True.

I use Kester rosin core solder (known to be very aggressive) with additional liquid rosin flux for soldering for even better soldering experience. It is wonderful for making good joints easily, but the board looks so dirty after soldering all components! I had to clean some just to inspect the solder joints under microscope. I wonder "no clean" weak flux would be a better option.
 

On Sun, Sep 24, 2023 at 10:09 AM, Ryuji Suzuki AB1WX wrote:
I use Kester rosin core solder
Isopropyl alcohol (90% is best) and some scrubbing with an old toothbrush will remove rosin flux.? The aerosol spray flux removers are effective but expensive.? I have had bad experiences with "no-clean" fluxes.
Don't try to use excessive flux as a substitute for proper technique and tip selection.??
73, Don N2VGU

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