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Re: QMX+ new build #qmx

 

Coincidentally just finished my build today, too. Here's the power output my QMX+ displays operating at 12.0V into a dummy load. I don't have a power meter to confirm and haven't done any optimization yet.?

160m: ?5.6W
80m: ? ?4.8W
60m: ? ?4.0W
40m: ? ?3.6W
30m: ? ?4.0W
20m: ? ?2.8W
17m: ? ? 2.8W
15m: ? ? 3.2W
12m: ? ? 2.8W
11m: ? ? ?3.2W
10m: ? ? 3.2W
6m: ? ? ? 0W (need to investigate)

Steve, W4SGN
Re: 10W amp distortion

 

Thanks Donald.? I suspect the LPF will be needed as well.? No filters used in the attached plot.
--
Brent DeWitt, AB1LF
Milford, MA
Re: QMX+ PA zeners #qmx

 

This technique was common with npn power amplifiers. It's generally not employed with mosfet finals. I don't recall myself ever damaging a qrp mosfet final. Whether a zener even aids survival of mosfet finals maybe someone else can answer.?

As for economics bs170 devices are pennies instead of multiple dollars for few watt npn. Also zener diodes may be more scarce now.?

Yes I have transmitted into the wrong antenna before. Another approach is using a efhw and first insuring it's connected.?

Curt
Re: 10W amp distortion

 

Is there a lowpass filter in line with the RF output?? Looking at this graph from QRP Labs
shows the 3rd harmonic at ~-12dBc, which would definitely need lowpass filtering before putting it on the air.
Yours likely has a similar amount of distortion.? This is characteristic of non-class A push-pull amplifiers, even harmonics are suppressed, odd harmonics, not as much.
73, Don N2VGU
Re: QMX+ new build #qmx

 

On Wed, Jun 5, 2024 at 05:57 PM, Jeffrey W Moore wrote:
...adding a switched pad...
This would be my choice, a 6dB pad is a fairly bulletproof protection scheme, and can be left in place after tuning if reduced? power (~1/4 power) operation is desired.
I use a resistive bridge between my QRP radios and tuner, which accomplishes the same thing.??
73, Don N2VGU
Re: USB-PD trigger cable voltage rampup -> possible QMX damage? #qmx #9v #power

 

Well perhaps I got lucky. I tested my 12V pre-set, right angle to 5.5 x 2.1 mm barrel plug adapter before trying it straight away on my QMX.

I saw the Power Bank battery putting out 12.01V? at about 0.01mA.

Though, I think I'll.make sure to cable up the battery to the adapter before inserting the barrel into the QMX as a routine sequence.

Greg


On Wed, Jun 5, 2024 at 8:04 PM, Paul - AI7JR
<paul.hanchett@...> wrote:

I don't think I quite understand...

The QMX is turned off until the left button is pressed... Doesn't all this voltage changing stuff happen long before the left button can be pressed? Or, is the PD waiting until the QMX actually starts drawing power, to ramp up ?

-- 
Paul -- AI7JR
Re: QMX+ new build #qmx

 

One possible hardware way to cut power to~25% for tuning would be to switch in a 39K across R525.
Re: USB-PD trigger cable voltage rampup -> possible QMX damage? #qmx #9v #power

 

开云体育

I don't think I quite understand...

The QMX is turned off until the left button is pressed... Doesn't all this voltage changing stuff happen long before the left button can be pressed? Or, is the PD waiting until the QMX actually starts drawing power, to ramp up ?

-- 
Paul -- AI7JR
Re: QMX+ PA zeners #qmx

 

I will fit them
Philip g7jur
Re: Talentcell battery pack alternatives?

 

Their site infected my PC with junk that my AV stopped.
I think I'll try other sources.? ?
73

On Mon, Jun 3, 2024 at 8:07?PM Dale - W7HLO <insidepassage_at_gmail.com_lastradioman@...> wrote:
Re: No receive QMX - help needed

 

Check C509
--
73
Karl
KI4ZUQ
Re: #qmx+ Announcing new QMX+ 160-6m multimode transceiver kit

 

Maybe the front and rear panels could be offered for sale to upgrade a QCX+ enclosure to a QMX+?
Re: QMX+ new build #qmx

 

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Wow - that is amazing! Congrats!!

Jim

On Jun 5, 2024, at 3:26?PM, Jeffrey W Moore via groups.io <jeffreymoore@...> wrote:

?Band LPF Power
_____ ____ _____
160 ? ? 0 ? ? 5.75
80 ? ? ? 1 ? ? ?4.47
60 ? ? ? 1 ? ? ? 3.7
40 ? ? ? 2 ? ? ? 3.57
30 ? ? ? 2 ? ? ? 4.68
20 ? ? ? 3 ? ? ? 3.16
17 ? ? ? ?3 ? ? ? 2.55
15 ? ? ? ?3 ? ? ?4.53
12 ? ? ? ?4 ? ? ?2.84
11 ? ? ? ?4 ? ? ? 3.83
10 ? ? ? ?4 ? ? ?4.08
6 ? ? ? ? ?5 ? ? ? 2.41

my LPF filter scans looked good so I didn’t try to optimize for power output by squeezing or stretching the coils.

i wound the output transformer with the RWTST variant. ?This is off of 12v supplying the rig. ?I measured with my scope.

--
Jim / K7TXA
Eagle, ID

SKCC 10447T
BUG 301
10W amp distortion

 

Started playing with a long neglected QRP Labs 10W HF amp yesterday.? Tried driving it with a QCX-mini on 20 meters through a 25dB attenuator.? Seems to make the correct peak power, but with lots of "dead time" in the crossover.? The IRF510 bias has been adjusted rather carefully, but I'm not sure about the BS170s.? Before I start taking things apart, has anyone seen this sort of distortion before (measured at the RF out into 50 ohms)?
My next step would probably be to tack in resistors in place of the IRF510 gates and look more closely at the drive.? Any other suggestions?

73,
Brent, AB1LF
--

Re: QMX+ PA zeners #qmx

 

Better to avoid high SWR than add non linear components and extra capacitance I think?
Re: QMX+ new build #qmx

 

I think the Atu10 uses latching relays. ?That’s an open source design I think. ?I’m not sure yet how I’m going to reduce power to the tuner to prevent bs170 damage. ?There are lots of options including reducing power supply voltage, adding a switched pad so that the QMX sees a reasonable impedance as you point out. ?The current mirror in the QMX is a great way to control voltage to the finals. ?But I don’t think there is a way to utilize that directly. ?I’m in the experimental phase now. ?This is such a great rig to play with some of these ideas.
Re: USB-PD trigger cable voltage rampup -> possible QMX damage? #qmx #9v #power

 

When using a trigger I always plug the trigger in first then plug in/power on the radio or other load.?
Why put the radio through the gyrations of trying to follow those voltage steps unnecessarily?
Re: QMX+ new build #qmx

 

Band LPF Power
_____ ____ _____
160 ? ? 0 ? ? 5.75
80 ? ? ? 1 ? ? ?4.47
60 ? ? ? 1 ? ? ? 3.7
40 ? ? ? 2 ? ? ? 3.57
30 ? ? ? 2 ? ? ? 4.68
20 ? ? ? 3 ? ? ? 3.16
17 ? ? ? ?3 ? ? ? 2.55
15 ? ? ? ?3 ? ? ?4.53
12 ? ? ? ?4 ? ? ?2.84
11 ? ? ? ?4 ? ? ? 3.83
10 ? ? ? ?4 ? ? ?4.08
6 ? ? ? ? ?5 ? ? ? 2.41

my LPF filter scans looked good so I didn’t try to optimize for power output by squeezing or stretching the coils.

i wound the output transformer with the RWTST variant. ?This is off of 12v supplying the rig. ?I measured with my scope.
Re: QMX Rev 3 Low Power Out Problem

 

Charles, the RX current is fine. The TX current is to high but not this much like assumed the last time.

Could you show please photos from your T501, one from each side with the holes?

I'm curious about the results from the oscilloscope.

73, Ludwig
Re: QMX+ new build #qmx

 

My QMX+ kit has just shipped.

Any thoughts on protecting the BA170 against the SWR spikes from an auto tuner.? Hopefully Hans will add a reduced power tune mode.? Or you could add a switched attenuator prior to the tuner.? Does the AT-10 tuner use latching relays?
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