Upon completion of my new build 20 meter qcx mini the initial power up produced a shrill, very loud tone. The tone does not respond to any of the controls. The only variable that I think I repaired was replacing a broken c14 on the main board. No obvious flaws after reviewing windings, solder joints, etc. ?Has anyone had experience with these symptoms?

Alright, I'm putting the soldering iron away, the input SWR is now as close to 1:1 as my Daiwa can read at 5w.

Here's what I did.
First, I rebuilt the QDX by replacing the BS-170s, the synth, and the 74ACT08.? I decided to run it again just for kicks thinking try two would be different.? I got several minutes on JS8 then it died again.??

So, I thought, why not "tune" the input of the amp with an LC circuit like any modern radio is capable of?? Against your recommendations I hooked up the NanoVNA again, got the complex impedance and set of to Google.? There's an LC calculator here that I decided to use:??.? I plugged in my numbers (22 ohms j-0.170) and then ran over to the QDX build manual to look for components matching the numbers I needed.? By the way, I now have three that are dead; the latest death from amp and two from a previous project that killed the uC. So, I removed L4 and removed one winding giving me 10.? I stole C30 and C31 then ran them in parallel to add their capacitances together.? I now had the LC components, now to install them.

I removed C3 from the 50w amp, stuck one end of the toroid in the hole going to the pi attenuator, connected the other end to C3, and reattached the other end of C3 to the RF input.? The two caps I stole from the QDX then got attached to the C3/toroid junction with a jumper run to ground (I used the screw hole on the edge of the PCB.??

Now my SWR is happy, the amp still puts out full power, and I'm done.??

Joshua

开云体育

Hmm, apparently it can be made to work, but what’s it good for?

I'm with Hans with this.

In order to build a valid simulation you have to know what you are doing?
if only to know if the sim tool fed you trash.? ?So you need to know what you
want and what is a valid result.

Typically you model, build and test to see if the model is valid for each
functional block.? Eventually you have enough block to make something go.

I do better than 90% of design using calculator (or slide rule) and my knowledge.
The exception is antennas as tools like EZNEC or my favorite 4NEC2 (also free!)
As it now only does the same evalutation as EZNEC but it has an optimizer
that once learned can do some slick tricks.

LTSpice is a very good tool but for RF you have to have all the parameters
and vaild models.? Also there is the free, student, and professional models
of the program. The student is not outrageously expensive and the professional
version can make your eyes bleed.? There is also Genesys, I think the company
was paying 6K$/year for that.

There are no software sims that can do " I wanna build a radio" and spits
out a design.

--
Allison
------------------
Post online only, please no email.

Some of the older Touch-Tone? keypads? (mid-'70s) would somehow generate the two tones simultaneously using only a single transistor.? And the Bell System frequency and amplitude matching requirements were pretty tight.? I never figured out how it was done....
73, Don N2VGU

With a red face I have to pass this along.?

I have built countless transceiver kits from both QRP Labs and Elecraft (K1&K2’s). I have never had a “problem” before the QMX I am building now.?

I had very low power output. After days of playing with the LPF I was ready to put it on the shelf for awhile.?

One last idea I reheated all the toroids. That did the trick I now have 4.7. - 5.1Ws on all band with the 9volt build.?

I had check all the connections with a meter but must have missed something.?

Now I’m patiently waiting for Hans to work his magic on the firmware updates.?

Larry NA0F

Hi,

I would first try to search for a "QMX" topics in a Search square of this group.
However, the FW is still in Alpha phase so the info is far from complete yet.

73 Bojan S53DZ

Hi Kees,

There are some interesting documents out-there but dont know if they are for QCX mini.
I suppose you should contact Martin DK3UW directly:
/g/QRPLabs/topic/multiband_qcx/86392526?p=

73 Bojan S53DZ

--Has anyone built or used one of these yet?
I'd like to know about it's performance before moving forward.
Wayne S.
KF7RCM

I just can't stop myself!
--
72,
Bill, N4QA

开云体育

I have the QDX and QMX Transceivers (still under development) with the much higher functions but also a small "pile" of single band QCX Mini's which I would like to "multiband".

73 Kees K5BCQ?

Does someone have a link to the above design ? Maybe it was just for the "standard" QCX+ ? Are there any other QCX-Mini Multiband designs out there ?

73 Kees K5BCQ

Hans I much prefer your more detailed March 3, 2022 explanation: --
73, Rick
VE7TK

Website:

On Tue, Jul 18, 2023 at 03:09 PM, Hans Summers wrote of G3RJV:

George once explained “why QRP”, he said: “Because it is a hobby we don’t have to do it - or mean anything - or fit into the world plan. As long as you can do one useless thing a day - life still has some meaning and that is the essence and the joy of life”.

Spot on!

It all gets absorbed and then one day , maybe a week or 30 years it suddenly provides
an answer to a problem, or a building brick.

That's why I'm forever reading decades old radio or electronics mags.
?
--
- 73 de Andy -

Yes, patience is required indeed!? My latest (small) order was actioned by Hans in a day or so.? TNT then sent me an email saying "Collecting" on 10th July. It remained at the same status for precisely a week.? On 17th July the status changed to "In transit" and today (18th) it has reached Istanbul.? From past experience, once it gets on a plane to the UK, things happen pretty fast!? Here's hoping!
--
Peter Lee
G3SPL