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Re: question 50 watts amp

 

I'm reading now what you have written.
Thanks.
hanz
Re: GPS antenna

 

Hello Tom
?
Has anyone tried using a GPS antenna as used on the Traquito just on leg of 1" that works very well on a U4B?

This type of antenna is a monopole antenna, like a 1/4-wave vertical. And like a 1/4-wave vertical, it also needs a groundplane (radials etc). Firstly 1" would?be 25.4mm which would not be the right length; at 1575 MHz L1 GPS a 1/4-wave antenna would need to be about 45mm (something like). The groundplane is formed by the groundplane of the tracker (Traquito in that case).?

However:?Traquito is a much larger tracker than U4B. Approximately 3x the weight?and 3x the board area. Therefore U4B would be an even less effective groundplane than Traquito.?

The antenna Dave VE3KCL used on the test flights, and I also used successfully, consists of a full-size dipole made from the same 0.33mm wire used in all the QRP Labs kits. Each arm of the dipole is 45mm long. Then make a "feedline" (and balun) by tightly twisting the wire for a distance of about 3-4cm (not critical). The result looks like a T with a shorter trunk than its arms; the vertical section is the twisted wire part, soldered to the U4B (ground and GPS Ant pins) at the bottom end, with the two horizontal arms of the dipole pointing left and right at the top.?

Furthermore Dave found that the performance is further improved by bending the dipole arms towards each other so that they are at 90-degrees. Now the antenna looks like a Y. Presumably improves the impedance match.?

I think this kind of dipole antenna outperforms most other types of passive antenna system. You see a lot of GPS ceramic "chip" antennas. These are a compromise, designed for when very little space is available. Your smartphone is a good example. That poor thing has to have a GPS antenna, WiFi, Bluetooth, Cellular, NFC, who knows what else... all crammed into a tiny case alongside a relatively huge screen, relatively huge battery, and tons of electronics. Having the space for a full-size dipole is a very nice luxury to have.

73 Hans G0UPL
Re: Ver 1 vs Ver4 QMX...going bonkers

 

Scott, I would make some voltage measurements.
These can all be done with just the bottom cover of the QMX removed, via the 8-pin and 6-pin power supply connectors you soldered in.? You just need to carefully identify which pin is which.
?
[the 8-pin connector]
1) Vin (JP102 pin 5) - should be the same voltage as your power source
2) 12V (JP102 pin 6) - should be 0V until you push the PWR_ON button, when it should immediately switch to the same voltage as your power source, minus a couple of tenths of a volt.
3) VCC (JP102 pin 4) - should stay at 0V until firmware is loaded, otherwise about 1/2 sec after you press PWR_ON, it should change to 5V.
[the 6-pin connector]
4) VDD (JP103 pin 4) - should be 0V until you push the PWR_ON button, when it should immediately rise to about 3V.? This is what powers the processor on to initialize the USB so you can load your firmware.
5) LIN_REG_EN (JP103 pin 3) - should start at 0V then immediately go to about halve the value as the 12V line measured above.
?
One of those is probably not working as described, which can lead us to the next troubleshooting step.
Stan KC7XE
Re: question 50 watts amp

 

Many thanks Jushua,
I have build the qmx plus for 9 volts.
For the cae not to use attenuators i am building now a variable output poeer supply based on a lm317 wiith a 2n3055.
Many for the points of attention.
73 hanz
Ver 1 vs Ver4 QMX...going bonkers

 

I have to say I have never had such grief with a build--ever. Including my own homebrew design.?
?
Having blown out the earlier qmx V1 a couple weeks ago I ordered some new boards and another QMX (v4). Being over paranoid I have constructed it meticulously...I am no Hans, but no stranger to solder smoke either. That said, I have once again fallen short.
?
Now before i go any further, and this is a faint hope, I am hoping someone will tell me the V1 Display and control board are not compatible with V4. I simply used those after building the new V 4 board as they are known to work fine--on my orig build, and on a friends QMX.
?
So, to the matter at hand. On power up sequence, nothing. No current draw at all, no recognizing the usb, no sounds, (no smoke) absolute silence). I have searched the questions here and have found some places to start when there is at least usb recognition , but this is truly ground zero.?
?
Scott
Re: QMX+ with ~1000 tone on 12M & 6M

 

Is this an issue related only to Version 1 of the board???
?
Ludwig, I was very careful inspecting the board, but it's perfectly possible that is the situation.? I will reinspect and make sure I can locate all 10 caps.??
?
Thanks & 73
Dick
W4PID
Re: QMX POTA Support...

 

I chose the 60-15m QMX for SOTA, as 40, 20, 15 meters are the bread and butter bands that are most likely to support SOTA activity.? 60m and10m are there for the ride but sketchy supporting SOTA water holes.? YMMV.
?
Brien - KE7WB
Re: QMX POTA Support...

 

Qrper.com - words and video?

-Mike/w1mt


On Thu, Jan 9, 2025 at 21:14 ta2rx bekir via <ta2rx.bekir=[email protected]> wrote:
Any suggested article available online?

73!?
de Bekir TA2RX

10 Oca 2025 Cum 02:42 tarihinde Ivica - YU1QRP via <yu1qrp=[email protected]> ?unu yazd?:
On Thu, Jan 9, 2025 at 07:13 PM, Ed Kwik wrote:
Go to YouTube. Search on ham radio sota
Or simply read a good article in 30 minutes instead of loosing time watching 3 hours of videos, same ammount of info and no forced ads.
?
?
Re: QMX POTA Support...

 

Any suggested article available online?

73!?
de Bekir TA2RX

10 Oca 2025 Cum 02:42 tarihinde Ivica - YU1QRP via <yu1qrp=[email protected]> ?unu yazd?:

On Thu, Jan 9, 2025 at 07:13 PM, Ed Kwik wrote:
Go to YouTube. Search on ham radio sota
Or simply read a good article in 30 minutes instead of loosing time watching 3 hours of videos, same ammount of info and no forced ads.
?
?
Re: QMX, one of op-amps self-oscillates at 25 MHz (or picks up the system clock?)

 

Hi Hans,

Feedback from a CMOS gate output to its input will result in oscillation at some frequency unique to each chip. It’s impossible to predict the oscillation frequency but in general, yes, it will typically be a high frequency. This is not good practice but if you want to bias a logic gate, you should use a pull-up and pull-down resistor at the input to create a half-supply bias. How is this different than using the feedback resistor? Well, the gate won’t oscillate continuously without feedback. Rather, thermal and/or electrical noise present at the input will cause the output to randomly toggle (no fixed frequency) or it may just get stuck high or low.

Using a CMOS logic gate as a high-gain amp is a risky practice. Logic gates are designed to be switches, not amplifiers for low voltage input signals. Running a 1V p-p signal into a logic gate powered at 3.3V or 5V will probably work but the totem pole input stage will carry switch-through current and may spend too much time in the linear region. This can cause unwanted high-frequency oscillation during each state transition. This is why logic gates have a maximum rise-time and fall-time spec - to minimize time spent in the linear region so the gate won’t oscillate during transitions.

A better way to implement this would be to use a Schmitt trigger biased at half supply using its positive feedback to rapidly pass through the linear region. Still, I’ve never seen a CMOS gate wired with a feedback component in my 45 years of engineering. In fact, doing such a thing would absolutely prevent passing design reviews.

Tony

On Thu, Jan 9, 2025 at 2:36?PM Hans Summers via <hans.summers=[email protected]> wrote:
Hi Tony

The 833 Hz is low-frequency oscillation, likely being generated in IC202. R207 (470K) is providing a DC bias at the input of the gate which can cause the gate to operate in its linear region, acting as a high gain amplifier rather than a logic buffer. I’m not sure why this gate has a feedback resistor as we never do this for logic gates for the very reason we don’t want them operating in the linear region.

It's a quite common technique to effectively DC bias the gate's input at almost exactly the midpoint between it's 0 and 1 input voltage thresholds. An AC coupled small signal connected at this input is then very well "amplified" by the gate, with very high gain, converting it as perfectly as possible to a 3.3V square wave. It's very effective.?

If there is no input signal at all, the gate will oscillate at some extremely high frequency, somewhere at VHF. But as soon as even a small input signal is applied, the gate locks onto it and amplifies it near-perfectly with very high gain (creating the square wave). Which is another way of looking at it.?

You will find in QMX if you remove this resistor, the gate will probably not operate. Zero output. Or certainly not reliably. Because now the small signal from the TCXO (about 1Vpp) is centered on what? Zero maybe? You have to provide some DC bias. You could put 1M to ground and 1M to Vdd or something. It would probably also work (modern CMOS are quite symmetric). But a better way of achieving the same thing is the feedback resistor.?

73 Hans G0UPL
GPS antenna

 

Has anyone tried using a GPS antenna as used on the Traquito just on leg of 1" that works very well on a U4B?
?
Tom
Re: QMX, one of op-amps self-oscillates at 25 MHz (or picks up the system clock?)

 

Adam,
?
You may be chasing a red herring.? In many older or even current inexpensive digital oscilloscopes, if you view the waveform at a much lower rate than its true value, you can see all sorts of sub-sampling effects and aliasing, showing what appear to be real signals, but are not really present.? This is because the scope firmware decimates the sampling rate it uses for low frequencies, causing aliasing if the signal is really at a higher rate. ?My new inexpensive digital scope does the same thing.
?
If your 25MHz clock was truly fully modulated by that low frequency 'signal' you are seeing, you would also see traces of varying amplitudes when viewed on the scope at 25MHz - but the 25MHz waveform is clean, no trace of varying amplitudes due to sinusoidal modulation, which would definitely be captured by the full rate sampling.? I think what you are demonstrating may be the effects of digital sampling in your oscilloscope, rather than a true modulating signal.
?
To verify, find someone with an analog scope and check with it.
?
Stan KC7XE
Re: QMX, one of op-amps self-oscillates at 25 MHz (or picks up the system clock?)

 

Hans Summers via groups.io <hans.summers@...> wrote:

Downstream of IC202 there isn't any "almost", this is the very reason why
IC202 is there. You will have a 3.3Vpp output at IC202 output.
I do. The scope shows some overshoots, but probably the probe needs to be
calibrated.

Can you take a similar video please for the signal at IC202 output?
Yes -- posted below.

I'm still having trouble trying to convince myself that the 25 MHz TCXO is
at fault here rather than - sorry to say it - some weird artefact
introduced by the measurement itself (at the TCXO output / gate input).
Don't be sorry -- in the realm of high frequencies I'm not sure of
anything :) HF never fails to find ways to surprise me.

BTW, I find this frequency weird as well. It's very low, compared to the
nominal frequency of the TCXO. It's probably way too low to result from
some stray capacitances or inductances.

It might be some weird artefact. But the oscilloscope never had such
artefacts before (I have it for 14-15 years), and symptoms (intermittent
CLK0 and CLK1 at 100 Hz, precisely the frequency of the buzzing both
audible in the speaker and visible in WSJT-X's spectrum view) fit.

Here's a new video with:

1. Output of the IC202 gate at various time bases

2. Signal from the TCXO with C203 (capacitor coupling TCXO with the gate)
removed -- so it's a signal on unloaded TCXO

3. VDD after L201 (so the power line of the clocking subsystem: TCXO,
gate, synth chip), showing some very minor ripple of the same frequency (I
suspect it's the effect of the problem, not the cause of it, but at this
point I'm not sure of anything)
Re: QMX POTA Support...

 

On Thu, Jan 9, 2025 at 07:02 PM, Len wrote:
plus anything else that I haven't even thought of yet :)
?
?
Some lightweight pole 5-6m or taler depending on the antenna you will be using. There are some nice packable solutions that are less then 0.5m in lenght when folded.
Re: QMX POTA Support...

 

On Thu, Jan 9, 2025 at 07:13 PM, Ed Kwik wrote:
Go to YouTube. Search on ham radio sota
Or simply read a good article in 30 minutes instead of loosing time watching 3 hours of videos, same ammount of info and no forced ads.
?
?
Re: question 50 watts amp

 

Consider looking closely at your 50w amplifier input SWR.? It may stress your QMX PA.? There are ways to address it.? I've written here about using the 50w amplifier multi-banded but I went a fully automated route.? You can easily swap out low pass filters on the amp output if you want a more manual approach.? Lowering the QMX power output is a good idea.? As Adam said, the amplifier input attenuator can get stressed if you do some long transmit digital modes with it.? On CW, it shouldn't be a problem.
?
Joshua
Re: QMX POTA Support...

 

Len via groups.io <kc3pwb@...> wrote:

Here's what I'm using:

- battery
4x 18650 + linear 12V regulator.

- antenna
PAC-12 / JPC-12 with a longer radiating element (5.6 m).

If you don't want to spend money on it, you can make a single-band dipole
or an end-fed (EFHW). From my experience, end-fed works better than a
dipole (it's easier to tune in the field). If you go with one of these, I
also recommend a strong line and something like this (I'm not sure how
it's called in English, a line throwing weight?):







I chose the heaviest one I could find.

You also need some hooks / carabiner clips:



The line has to be strong in case your weight gets stuck on a branch (and
make sure you tie it properly to clips). It happened to me several times.
But after one season of playing with dipole and EFHW, I ordered PAC-12 and
it made everything so much easier. No more ropes, weights, trying to find
a tree, etc...

The radiating angle of a vertical antenna is also better for DXing.

- tuner
I don't use a tuner. I tune the antenna with NanoVNA. Another thing to
remember, always make sure that the VNA is charged. The same with radio
batteries.

- plus anything else that I haven't even thought of yet :)
- speaker / headphones
- voltmeter for 18650s (before the regulator)
- some comfortable holder to put a key
- a lightweight chair (optional, you can sit on the ground)
- a lightweight table (optional, but it's easier to make notes this way)
- something to write on (pen, paper)
- head lamp for when it gets dark (with a head lamp you still have two
hands free)
- a feeder (I'm using 15m of a H155 cable + a choke on it)

If you don't want to carry a chair and a table, I recommend doing notes on
a smartphone instead of on paper (some notepad app, I'm using Colornote).

If you want to work in a group (for example with your local club), I
recommend using headphones instead of a speaker. It's easier to focus with
headphones, and you're not interrupting others.

Some tips when working in a group: split bands (so if you're working on
20m, it's good if someone else uses a different band), be mindful when
tuning the antenna (it sweeps the band, so it causes clicks in other
radios), be mindful of automatically activated PAs (my QMX enabled PTT in
the PA of a guy sitting two meters from me, it was microPA 50).

You might want to see my video from building a useful addon for portable
work:

Here's how it looks like on a field day with my local club:
Re: New build QMX - high noise on all bands

 

Just to close off this thread, following Jeff Moore's WiKi page I injected a signal of 10mV and looked at the output of the 4 Op Amps and saw the expected approximate 12kHz signal at 10 times the input signal so this did indeed seem to confirm that the PCM1804 was probably faulty. Out of interest the 4 Op Amps on my board are LT6231's instead of LM4562's presumably due to a supply issue at the time of manufacture - I suspect it is a good drop-in replacement. I plucked up the courage to replace the PCM1804 using techniques posted on this forum which is a great source of information. The noise dropped back to S0 and comfortably received a high level injected signal. All the self diagnostic plots from PuTTY now look as expected. I used WSJTX to receive WSPR signals from all over Europe and one from Australia so I think the receiver is working well now and I can start playing with my QMX.
I had actually set this construction project as a learning exercise for my son who did a great construction job. It's a shame that a surface mount chip turned out to be faulty. I had never intended to do surface mount work so this forced me out of my comfort zone which is sometimes no bad thing.
I think this is a great little transceiver and a good way to get started on the HF bands. I particularly like the built in SWR bridge allowing SWR and power measurements as well as all the self diagnostics which is great for people with not much test equipment. Well done to Hans and the team and thanks to Jeff, Ludwig, Gus and everyone who posts on this forum.
Re: question 50 watts amp

 

Many thanks Bojan for the information.
Good to hear it works fine.
I would like to make the QMX with PA ?my second station besides my IC7300.
The main reason is the full break in, i really like this.
?
73 hanz
Re: question 50 watts amp

 

Many thanks Adam for the information.
?
73 hanz
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