Re: U3S Drop out on Tx

Try it into a dummy load to see if it’s RFI

USB noise

开云体育

I have my QMX+ with me in Tanzania, so I have a compact and easy to set up radio as I travel.? I am having a big problem with USB noise.

noise level is high enough to obliterate most signals
FT4/FT8 are unusable due to suppression of signals by noise
I can't use a USB isolator because my computer takes USB-C inputs only.? A standard cable USB-A cable with a USB-C adapter does not allow the radio to be recognized.
This problem is not apparent with my QDX, and very minimally on my KX3.
The QMX+ picks up birdies about every one kHz when the USB cable is plugged in and active
Laptop is a Dell XPS-13 9315

Are there any solutions for this?? Any bypassing that can be added.? Suggestions??? I'd like to operate FT8 but as soon as I plug in the cable the stations are all masked by noise.? Clearly there is noise being generated in the laptop, but the QMX seems to have absolutely no suppression to deal with it, unlike most of my other radios.

73

Charles
5H3DX
NK8O
VE3ISD

QMX and SOTA equipment organization

#139801

I used my QMX (60-15) on a SOTA activation this week. I use a linked dipole in an inverted vee configuration on a telescoping pole so no need for a tuner. It works well but I found that juggling all the parts and pieces while trying to make contacts on a windy peak was a little clumsy.? So I am experimenting with this setup.? It is a modified/repurposed plastic clipboard.? I have mounted my battery pack, converter, amplified speaker, CW paddle and QMX on the clipboard.? I moved the clipboard clip to the side so it will hold a folded sheet of paper for logging.? The paddle, speaker and QMX snap into 3-D printed brackets.? For now the battery pack and converter are mounted with velcro.? All items are removable for transport.? I will add a 90 degree BNC adaptor for optimum feedline routing.? ?Not pretty but functional.

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Brien - KE7WB

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U3S Drop out on Tx

#139800

Just built a U3S with relay board and QLG2. 7805 equivalent in TO220 case for 5V power. Was working perfectly for a few day's testing.?

then tx started cutting out a few seconds to half a minute after Tx. Turned out voltage was dropping to 4.90 (measured at input to main board) and processor was resetting. Current draw at this point was 280 mA. ?Non transmit current 140 mA. Power output with single BS170 was 200 mW. Processor never resets when in non transmit mode.?

I have touched up a number of the power solder joints (altho they looked fine before) with no change in behavior. Turning down the drive to BS170 to where output was only 100 mW allowed completion of transmissions.?

powering with known good 5V p/s directly did not solve the problem.?

Any idea where to go from here?

--

73, Dan? NM3A

Re: Does L502 cause excessive voltages on the QMX finals?

#139799

Evan,

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I had read the LT-Spice docs and used some of the advanced features a few years ago.

Comming at it fresh late yesterday, it was all I could do to edit a schematic and get a transient analysis going.

I had enough head scratching to do without dealing with advanced features.

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You may have noticed that for the 1:1 version of T501 that I was using, I assumed the inductance

of the two primary windings added together should equal the secondary inductance.

Unfortunately, the two primary windings interact on the same core to give a larger total inductance for the primary.

Instead it is the total turns count of the primary windings that is equal to the secondary winding turns count for a 1:1 transformer.

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Here's how I now think of it:

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############

Inductance on a given core is proportional to turns squared.
Lets assume an AL of 1uH per turn for the core, a 16uH secondary, and a 3:2 turns ratio.
Then the number of turns for a 16uH secondary winding is sqrt(16) = 4 turns
? (working back we have: ? 1uH/turn * 4turns**2 = 16uH)
The total number of turns on the primary is 4 * 3/2 = 6 turns
Each half of the primary has 3 turns.The inductance of each half of the primary is: ?1uH/turn * 3**2 = 9uH

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In general the formula for the inductance of one winding of a center tapped primary given a turns ratio of N:1and a secondary inductance of Ls is:

L_one-primary-winding = ( sqrt(Ls) * N / 2) **2?
For the above example:? ? ( sqrt(16) * (3/2) / 2 ) **2 = 9

############

?

I've used the above to adjust the transformers in the new simulation schematic QMX_sim04.asc

In addition, I changed the turns ratio of T501 to 1:1 for the "Stock with L502 removed" case.

This increases the output to be slightly more than the stock case, but Vds-max across the BS170's is far less than the stock build.

There may be reasons not to do this, but it is worth investigating since the change in build proceedure would be trivial.

If we use this scheme, then everybody builds the QMX with the simpler 9v version of T501, but 12v builds short across L502.

There should also be a 0.1uF cap to ground at the T501 center tap if L502 gets shorted.

?

Here's some figures for peak voltages using QMX_sim04.asc:

Vds? ? ? Output
38.3? ?21.4 ? ? ? ? ? ?Stock QMX, has 3:2 turns ratio on T501
23.8 ? 17.5 ? ? ? ? ? ?With L502 removed, still has 3:2 turns ratio on T501
23.0? ? ?21.6 ? ? ? ? ? ?With L502 removed, now has 1:1 turns ratio on T501

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Note that I am showing 38.3 for Vds-max across the BS170's when simulating a stock QMX at 3.57 Mhz.

Chris reported in a forum post that he measured well over 60 volts using a scope on a stock QMX.

(Unfortunately his graph has been removed.)

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With the 1:1 turns ratio at T501 and with L502 removed, I see a Vds-max of only 23v

and 21.6v across the load. The power into the 50 ohm resistor is? ?(21.6*0.707)**2/50 = 4.66W

My simulation for a stock QMX 12v builds shows slightly less, but real world tests can give over 5W.

?

That's all just in simulation, should be interesting to try it on some hardware.

And try it with a whole range of complex impedances at the antenna port, not just a 50 ohm dummy load.

Once we figure out operation at 3.57mhz we might find 4.0mhz significantly different.

And then we only have another dozen bands to figure out.

?

It's complicated!

?

Jerry, KE7ER

Re: N1MM Logger+'s built-in spectrum display works with QMX I/Q output now

#139798

I am trying to get the N1MM+ spectrum display working with my QMX+.? I have successfully loaded N1MM+ and modified the function keys to include the KY nomenclature.? The function keys and CAT commands are working properly.

?

I downloaded exto_qmx.dll file and copied it from my Download directory to the N1MM+ directory.? When I open N1MM+ and open a spectrum display window I receive the following, "Error opening .\extio_qmx.dll Closing SDR Server".? Also, the lower right corner of the spectrum display is showing the same frequency as the entry window and QMX+.? Please help me understand how I can correct this.

?

Howard N8HO

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Re: Higher SWR Dummy Loads ??

#139797

I put a 50 Ohm dummy load on the antenna side of my ZM-2 tuner, and then connect rig to the transceiver side of the ZM-2.? I can then dial in a range of complex impedances by changing the capacitors and achieve a particular SWR.? Same can be done for a different kind of manual tuner.?

?

If you want a resistive-only load to achieve a particular SWR, you can use a resistor across the BNC port.? For example, ~100 Ohms will give an SWR of 2:1, as will ~25 Ohms.? You would likely need to put some resistors in parallel to achieve your desired power rating.? Then you would need to calculate the individual resistor value so that R/n gives you the desired resistance.??

?

73

Mike N9OHW

Re: Linux Mint 22.1, WSJTC 2.7.0 and Hamlib

#139796

Try this Bill!!!

Re: Higher SWR Dummy Loads ??

#139795

You can read the VNA results at . It looks legit.

This is the finest piece of hillbilly engineering I've seen since the Wouff Hong. :)

Re: U3S- ideas for aux switch #u3s

#139794

Sorry it took a while to find the manual it has been 4 years sense I built it. ?The screwdriver is pointing at the + feed point fir the LED. I picked up the - from the switch below the LED.

Re: Higher SWR Dummy Loads ??

#139793

The above was in reply to a suggestion of using a tuner for VSWR testing.

73, Don

Re: Higher SWR Dummy Loads ??

#139792

Be careful with this, the VSWR you set will likely be wildly different at the harmonics than at the fundamental, and it will cause a different response than a resistive mismatch would, which is the same VSWR at (almost) all frequencies.?

This can be easily checked/verified with a nanoVNA, just set the markers to the fundamental, and to the harmonics which will likely look terrible.? Recall that one of the touted advantages of tuner is harmonic reduction.

The tuner method might for example excite an oscillation which might not occur with a resistive mismatch.

?

Another method is to use a short or open after an attenuator, a 3dB pad will yield 3:1VSWR for example.?

You can reverse the phase by swapping open and short, or vary the phase by varying a tank circuit through resonance as a load.? You can get almost 180° phase change in this way.?

We used this at transistor manufacturers for load-pull testing and could get 20:1 VSWR with a low-loss tank at 2 meters.

?

I have set up tests at 4:1 using terminations and tees, I could have gone further but I ran out of tees.....

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73, Don N2VGU

Re: Does L502 cause excessive voltages on the QMX finals?

#139791

Jerry,

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Not sure if you are aware of two features in LTSpice:

1 - You can use Math expressions for the plots.? Here is one comparing the power as V(n003)*I(R1).? You can plot the current through a device.

?

2 - you can get the average value with <ctl>left-click on the plot value:

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Unfortunately, you can only get one value at a time.? It is also better to zoom in to a steady state:

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There is a good YouTube series that teaches advanced LTSpice commands:

And the online manuals:

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73

Evan

AC9TU

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Re: Higher SWR Dummy Loads ??

#139790

On Thu, Feb 27, 2025 at 10:18 AM, Joe WB9SBD wrote:

Made simple, the two wires are 12 ga copper, about 6 inches long.? Open at the far end.
Simple center conductor goes to one wire, Braid to the other.

I was a contractor to Fort Monmouth, home to the Army's E-Labs until the fort closed.??

They had a megawatt-level dummy load for testing power supplies.? It was essentially a swimming pool filled with copper sulfate solution, with a pair of huge graphite electrodes.

There was a crane which moved the electrodes in and out of the water to vary the load resistance.? Just a bigger version of WB9SBD's.

73, Don N2VGU

Re: iPhone camera adapter, receive but no send?

#139789

Very clever!? I'd love to see some details for the transformer build and maybe some pic's of the details of the chalk box build, if you have time.? No counterpoise?

Re: Does L502 cause excessive voltages on the QMX finals?

#139788

Evan,

?

You are correct, I missed the 100pF cap.

Thanks.

?

I had noticed that computed values for L508 and L512 were different than the ones Hans had said he simulated with.

I figured since I was simulating may as well go with those, and that final windings got adjusted when he was looking at hardware.

?

I have made both adjustments to the simulation in the attached file QMX_sim03.asc

?

Will try your 3:2 12v transformer, but haven't yet.

In simulation it may not make too much difference, I'd expect that all the voltages after the transformer just go down by that ratio.

From forum posts, it seems people have fewer failures of the BS170's with a 9vdc build, so I figured I'd start with that.

However, perhaps that's only because most people have built for 12vdc.

It does seem that with the higher currents of a 9vdc build we would have more trouble with overheating in digital modes.

?

Here's the voltage readings from LT-Spice for my original QMX_sim01.asc simulation before and after your changes.

Curious that adding changing the L508 and L512 values brings the output down, but adding the 100pF cap brings it most of the way back up

Output: ?

? ? ? ? ?18.6v as in sim02
? ? ? ? ?15.6v when adjusting L508 and L512 to AL*(t**2) values of 1.875uH and 1.452uH
? ? ? ? ?18.4v when 100pF added
? ? ? ? ?18.4v when both changes made

?

I then looked at that final version with both of your changes, and compared it with the same but without L502,

and also my VMCD and CMCD versions as in the attached file QMX_sim03.asc.

Since Vds-peak values can blow the BS170's, I also looked at peak voltage on one of the drains.

? stock (with both changes) ?vs L1-removed vs VMCD vs CMCD:
? ? Output? ? ?18.4 ?vs ?13.8 ? vs 14.4 ?vs ?18.5
? ? Vds-max? 33.8 ?vs ?18.5 ? vs 18.5 ?vs ?27.5

?

? Output with L1 removed is 13.8v as shown, but goes higher to 14.1v if L508=1.83uH,L512=1.55uH)
? For VMCD, FET voltages are square and current is sinewave, for CMCD current is square and voltage is sinewave

?

Note how much lower Vds-max is for L1-removed and VMCD.?

L1-removed is effectively VMCD, but using the stock LPF which I am still unsure of.

L1-removed and VMCD both also have low output power, which is a function of the square of the output voltages recorded above.

If we were to increase the transformer ratio of the L1-removed version such that Vds-max was equal to that of the stock QMX,

it seems the output voltage should increase to a value of 13.8*(33.8/18.4) = 25.35, which is way beyond the stock output voltage of 18.4

That's the reason I was sucked into this, removing L502 may help with the over-voltage issue at the BS170's

though this may bring on issues due to higher peak currents.

Like all things around RF amps, it's considerably more complicated than one might think at first glance.

?

Anyways, I was up half the night here with a hacking cough, which is why I got that simulation done.

Probably time to get some sleep.

Given my current state, could well be plenty more errors in my attempts at simulation and in the above discussion.

?

Jerry, KE7ER

Re: Has anyone built the 10 watt PA kit and used it with the QMX?

#139787

On Thu, Feb 27, 2025 at 08:57 AM, ajparent1/kb1gmx wrote:

Generally using that amp at the output of a radio that does

3-5W is barking up the wrong tree.? IT also does not increase the

power enough to be significant (20W wold be a marginal increse)..

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My rule of thumb is 10dB gain minimum, maybe 6dB for a device for which no higher power alternate exists.? Pretty much what Allison said.

?

There is an amplifier figure of merit called "power-added efficiency" which is?

(Pout-Pin)/(Vsupply*Isupply)

When the gain is very low this metric becomes very small.??

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It seems like madness to have a 20dB pad at the input of a 23dB gain amp.? It makes for a good input return loss, though!

73, Don N2VGU

Re: 10m low pass filter values for PA50W #50wpa #lowpass #pa #10m #50w

#139786

And thank you verry much also AkI. This was exactly what I was looking for.

vy 73 Michael DB2GM

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Re: 10m low pass filter values for PA50W #50wpa #lowpass #pa #10m #50w

#139785

Hello all

thank you very much for your inputs and comments. The links help me also for future calculations.

vy 73 de Michael DB2GM

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Re: Higher SWR Dummy Loads ??

#139784

I bought a couple of Hans' dummy load kits (because of their great design) and populated them with different values of resistors.

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For a 100 Ohm load: 10ea. 1K 1% 2W resistors.

For a 200 Ohm load: 10ea, 2K 1% 2W resistors.