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It's a great thing to have a waterfall display on a radio. Even better, if it's from a second receiver, that can be used independently. That way, one station can be worked, while simultaneously exploring different signals on the band. Also, turning the dial can become touching the screen. Not the way to go for everyone, but I love it...

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QMX+ has an I/Q mode, that uses the soundcard as interface, allowing for a panadapter. A perfect solution for CW operation: Everything you need. Not-so-perfect for digimodes or future SSB, though: Those modes do need the soundcard for the audio data, so the current implementation does not allow for the use of the I/Q mode in the same way you can do in CW (this sentence may contain wrong assumptions as I do not have QMX at hand, yet). Also, the manual states, that the I/Q data delivered over the soundcard is not suitable for decoding digimodes. I remember having read thoughts about a? possible future implementation of a different type, maybe QMX+ will have that feature out-of-the-box some day, but while Hans is busy on ticking the SSB-To-Do-List, maybe it's not the right time to propose even more features...?

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So I'd like to come up with a different approach:

On my analog TRXes I had the same no-waterfall-issue. It could be solved relatively easy, by tapping the intermediate-frequency (using a buffer board like iface2 from tspelettronica) and feeding that signal into an SDR-receiver. The frequency syncing is done by polling the working freq via CAT from the TRX and feeding it into the SDR-software. That should be possible with QMX+, too, shouldn't it? Unfortunately my knowledge is very limited, so maybe the forum can help?

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* What I like to obtain is the analog input signal from the antenna (or intermediate frequency, if there is one) - to be able to feed that in a second SDR-receiver. The signal should be taken from at a point after the LNA , but before any narrow filters are applied. Thus, the antenna signal should not be worsened for the receivers and the second RX should get a broadband signal.

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* Also, the signal should be taken at best at a point that will never see the TX signal, so that my SDR receiver will have a long an peaceful live. If that's not possible, the buffer board mentioned above takes a 12V signal for PTT, that will isolate the circuit, while sending. In that case, I would need to know, where I can get the RX/TX switching from the QMX board.?

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Maybe someone could point out a suitable tap-point for the freq-out (and, if needed TX-detection) on the circuit board of the QMX+?

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* Tapping the signal directly would draw power and that would probably interfere with the inner-workings of the QMX. That's what the iface2 buffer board is for. It copies the signal without drawing significant power. The delay introduced is negligible, the software delay from the subsequent software processing is much greater. That buffer circuit worked great on my analog TRX, it should on QMX+, too, shouldn't it?

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* Am I on the right track? Maybe there's a different / better approach to get that panadapter feature. Any suggestions?

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P.S: My QMX+ is still climbing up the assembly-list (making good progress!), so this question is purely theoretical for me, right now. It will become more relevant in the near future, though and I might order that interface patine, which also has some delivery time in order to have everything ready when QMX arrives. I sure will post the results here, it just may take some time.

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Any help is appreciated!

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Yours Joe, DJ0CHE

This post has scrolled down really fast. Maybe this reply will get it a bit more focus. I'd really like to know if I'm on the right track - and I'm lost in looking for a good point on the board to tap the frequency (including to know if it's RX-only or if i need to tap on a point which also gets TX, meaning I would need a point to get rx/tx info. Any help is appreciated!

On Fri, Feb 21, 2025 at 01:07 PM, Alan G4ZFQ wrote:

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Thank you for your reply!?

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IF tap is not possible.

That's what I thought, I'm assuming, there's no IF at all?

With very delicate work you might get IQ out independently but would need to be skilful and just end up with the same output as the QMX standard IQ out.

My current approach is not to get I/Q separately (although this might be a viable solution, too), but to 'tap' the analog RX signal (or IF, if available) and convert it to I/Q, using an independent SDR receiver. The I/Q mode as-is does not fit my requirements.

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I don't have a block diagram for the QMX and the receiver schematics are not an open book to me. So my question is: Is there any point in the cirquit where I can 'tap' the analog RX signal (using a buffer board in order not to draw power from that signal)?

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It's always possible to get the RX signal directly from the antenna input. That will work. However, I will have to cut that connection on TX in order not to fry my second receiver. The buffer board I intend to use, does have that ability. In that case I need a point on the circuit, where i can 'read' the RX/TX status. I will have to convert that signal to +12 V for the buffer board. Using CAT is not an option for this case, because it's to slow.

There is a fundamental lack of understanding of the SDR receiver.

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First there is essentially no IF, its direct to base band which is the

IQ outputs.? All the work is done in the digital realm by the

ST32M4xxx mpu.

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For second receiver the bandwidth of that down conversion is

Relatively narrow band so the panoramic view (waterfall) would

be narrow as would the frequency of the "2nd" receiver.? Doing

a close in waterfall is taking what data there is (IQ outputs)

and translating that to a display format.

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Generally the idea of upstream tap is limited to radios that

are multiple conversion superhet transceivers.? That is typical

of many radios like ft817, FT450, IC756 and a large number?

of others.?

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Allison
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Post online only,?
direct email will go to a bit bucket.

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--QMX+ has an I/Q mode, that uses the soundcard as interface, allowing for a panadapter.

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Allison
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Post online only,?
direct email will go to a bit bucket.

Okay, but what about using the signal from the antenna-input directly? I can't use an RF splitter / power divider to the non-amplified signal, I might get away with that buffer board? Not sure about the usable bandwidth, though. Might be worth a try. In that case, I still need some sort of? RX/TX signaling, in order to tell the buffer board when to disconnect.

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If that approach is not viable at all, I might have to dig deeper on how to get the I/Q data directly. Although, I'm assuming that's better done in software. I'm aware, that the QMX firmware is under active development and at some point in time we might get an API, which would, if capable be a fist-class solution. I'm unsure, though what priority that feature has, and we can't expect Hans to do all at once. Therefore, I'm looking for alternatives. Also, I like the idea of processing the analog signal with a second, independent device.

You can read more about the QMX receiver design in the QDX assembly manual - Hans did not repeat the design description for QMX.

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As others have said, there is no real IF.? If you really want to pursue your idea with the RF, you may be able to tap it after the tx/rx switch at the output of the band selector mux, but it may decrease the receiver performance, since it is an unbuffered signal.? Then as Allison notes, you will be limited to the relatively narrow bandwidth of your SDR receiver for your panadapter display.?

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For me it works to just use the IQ output directly through the USB port into SDR software, which provides a 12kHz panadapter display for CW, which is adequate.

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Stan

And if you want to do it fully externally,? the QMX does have a PTT signal output that you can use for rx/tx switch.

This tread has hit a nerve.? I plan on doing something like this with my QMX+.? Proposal is to use a hi-z input buffer board at the receive frequency inside the QMX+ and send it to an AirSpy Discovery Plus mounted internally in the QMX+.? I can then use either HDSDR or SDRSharp as a pan adapter *and* a second receiver on my laptop.? This would require two USB cable to the laptop - and I presume the QMX+ and the SDR program can control each other (OmniRig?)? I do this with my TS-590.? If I want to use the QMX+ portable without the pan adapter, I can.? The AirSpy unit is tiny and light and gets power from the USB port.? So it doesn't draw power if it isn't plugged into a USB port.

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Many variations possible here....? SDR dongles, programs, etc.? I like the AirSpy with SDRSharp - the DNR in SDRSharp is the best I've used.

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73 Dave kx3dx

The receiver gets RX_IN from Q508 in the upper middle of the final page of the schematics (page 5).

Q508 is where the transmitter is blocked from the receiver, though there will still be

a very strong signal on RX_IN when transmitting.??

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The receiver is on page 4, RX_IN goes into IC408 which steers the signal into the appropriate band pass filter,

IC402 selects the output from the appropriate band pass filter and has the received signal coming out on pin 9.

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So your SDR receiver could grab RX_IN, or it could try grabbing IC408 pin 9 and get it after all the local

AM broadcast band stations and (most of) the other amateur bands have been filtered out.?

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A buffer is a good idea, driving coax to your SDR receiver.

Mostly because you don't want a bare wire picking up other crud from the SMPS's and such.

No buffer would probably work fine, an extra 50 ohm coax load on RX_IN would drop the received signal

for the QMX by maybe 3dB, or half an S unit.

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You might want to use the "RX" signal on page 5 to desense your SDR receiver somehow,

perhaps by clamping the output of your new buffer when "RX" is logic low (0v).

"RX" goes low when transmitting, logic high (3v) when receiving.

Seeing some of the transmitted signal on the SDR could be a good thing,

it will tell you exactly what the receiver is tuned to.

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Your SDR receiver will inevitably see a very strong signal from CLK1 and CLK2 going into IC403

a few KHz away (12 KHz?) from the received signal.? Since they are at the same frequency?

but 90 degrees out of phase, they will be seen as a single signal.

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Using a cheap RTL-SDR type receiver for your panadapter might be sufficient.

If it works well, I'd expect such a solution to be very popular with QMX users.

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Jerry, KE7ER

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On Fri, Feb 21, 2025 at 07:15 AM, <410733@...> wrote:

Hi,

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It can be done using an electronic T/R switch in parallel to the antenna port and controlled by a PTT signal.

I have used this with several QRP radios feeding a RSP1A SDR.

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73,

Roelof, pa0rdt

Thank you all, for your valuable replies! I did, indeed, only read the QMX docs - even though it is mentioned on various locations that one design is based on another so now I have to ask myself why I did not use that obvious sources of information...

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On my superhets, I do use that buffer-board on the IF with great success, using the not-so-cheap Airspy-HF, I have great signal quality to work with, be it in GQRX, SDRangel, GnuRadio or even feeding it to flgigi / wsjtx after converting it to audio. Most of the time, working on SSB, I just use the panadapter do have the signals on the band in view - and checking out some new signals while working a pileup...

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I do now have a lot of information to work with - and a lot more manuals to read. I even found the longed-for block diagram. That, besides all the real-life necessities, should keep me busy some weeks.

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If someone has anything to add to: Please feel free, I absolutely appreciate it! I might come up with more questions down the road... and hopefully with a nice solution at a later stage!

This might interest some. It could be used with a switch that turns this receiver's RF input off when the transceiver is transmitting. Several companies make these switches.

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So, what I did while using an old crystal controlled transmitter, combined with an SDRplay RSP-1, was to put an RF triggered TR switch between them. That could be done with a transceiver like the QMX too. I used the 4SQRP K8IQY Magic Box for that. The SDRplay receivers are great receivers all by themselves.?

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73, Dan - W2DLC

Just to give you an update: For the first step, I opted to order that device: . From what one could read, this will do the trick, it's ready to use and affordable. The hints KE7ER gave are indeed very helpful, I might try that at a later stage - but as you stated, running coax to that circuit board may not be the best solution and even if everything goes well there will be unwanted signals in the waterfall. The advantage I hoped for is not to worsen the receiving signal - so every solution has its disadvantages. Using that kind of switch seems to be the less-risky option to get a nice panadapter along QMX+. And, maybe one day I/Q mode will be usable in parallel to normal operation rendering that approaches superfluous.