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QMX/QMX+: Steps to safe antenna tuning and powering the unit

Andrew
 

Being a new to CW and and these transceivers, reading the forums I am a bit worried of damaging the unit when I get it hopefully by the end of June.

First concern is powering the unit.? I know it wants 12v max, my 3Ah Bioenna battery has a nominal voltage higher than that at least when fully charged, Hans has recommended placing several diodes in series to reduce the voltage.? In trying to keep things universal and simple, I am thinking of placing a small voltage reducer to limit the output power of the battery to 12v or a bit under.;using something like this device:



I prefer to keeps my equipment uniform/universal and not having a bunch of batteries of different voltage.

Second, I recently acquired a Elecraft T1 to use with it and an IC-705.? The threads indicate that during tuning the swr could hit 10 which could still damage the QMX+ even with the protection on.? The T1 specs has min power of 0.5 watts with suggested power of 2-5 watts.? Tuning mode on the QMX+ reflects 25% or perhaps at best around 1.25 watts if the unit is putting out 5 watts.

So, I would appreciate if someone could provide some guidance into how to best power the unit and tune the antenna (EFRW).? I also have EFHW atennas, but some conditions may require the random wire version.
 

On Thu, May 30, 2024 at 12:01 PM, Andrew wrote:
So, I would appreciate if someone could provide some guidance into how to best power the unit and tune the antenna (EFRW).
I suggest placing a resistive VSWR bridge (I have a QRP-O-Meter) between the radio and tuner.? Set to TUNE position, its 6dB loss will limit the VSWR the radio sees to under 2:1during tuning.? When the antenna is tuned, bypass the bridge and full TX power will be available.??
73, Don N2VGU
 

Easy....

Using a TI or any other auto-tuner the same set of risks are a fact.
Same for manual one!

You have a IC705, use that to match the antenna if needed while employing
the T1 autotuner.? Then without changing the T1 remove the 705 and
connect the QMX to a known now matched antenna.

My prefered:
For harmonic bands like 40/20/15/10 I use a endfed HW that is already
tuned and no need then for a TI or other matching unit.? Mine on those
bands has a SWR under 1.3:1, more than good enough.

When a tuner is needed I use? manual matching unit with a
Tenna-tuner (Qrpkits) to dial in it, MFJ259B or similar.? Then
connect the QRP radio.? Extra steps but far quicker than
blowing the finals and replacing them.

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

On Thu, May 30, 2024 at 09:27 AM, ajparent1/kb1gmx wrote:
Tenna-tuner (Qrpkits
Can you clarify the procedure for using a manual tuner and the Tenna Dipper II??

Note, I also have a Z-match tuner (which I have not tired out) and RigExpert Stick 500 which I have used to tune an EFHW antenna wire.
 

Safe options:
1. Tune with 705, then connect QMX
2. Resistive bridge in front of any tuner - switch to straight thru after tuning up. A lot of manual QRP tuners integrate this into the tuner
3. Use tuning mode on the QMX during any tuning. Should be safe to use the T1 with this. Should be safe to use any automatic tuner this way, although many won't tune with the low power. Just be careful that the tuner does not automatically retune during use.?

4. Tune with significantly reduced input voltage, eg. 7 V for a 12 V build QMX.?


Unsafe:
Using full power and no bridge with any tuner.?
--
73, Dan? NM3A
 

I made my own 'battery reducers' from 2A or 3A diodes in series.? You don't need a complicated circuit to?do this.
Each diode drops the voltage by about 0.7V.??
So, with a 14.4 V battery, and three diodes in the (+) lead, the transceiver would see about 12.3 V.? Four diodes would give 11.6V...etc.
Just don't fall below the minimum voltage required by your radio.
I used heat-shrink tubing and color-coded Anderson Powerpoles to keep my reducers small and neat...a color for each different voltage drop value.
I pick the right 'reducer' for the voltage I need.... or for the tuning needs of the QRP radio.... or for the desired output.... such as <5 watts.

I like the Kanga Kits (UK) pocket transmatch tuner.? ?It is a "Z-match" and uses a resistor network when placed in the tune mode.?
?The much larger Emtech ZM2 z-match is similar;?tune the capacitors to dim the LED for a match indication.
Not many SWR worries with either?tuner.? The resistor bridge is a better (safer) load than firing directly into an antenna tuner.
You tune?a Z-match to dim the LED.... lowest or no LED indicates lowest SWR, and I've checked with an antenna analyzer and tuning this way is pretty accurate

Resistive bridge kits, as used in the tuners (above) are available without a tuner... so it may be possible to use one between your tuner and radio.??
I think Pacific Antenna (US) and Kanga Kits offer them.

73
Jay
W6CJ






On Thu, May 30, 2024 at 9:02?AM Andrew <averacpa_at_bellsouth.net_lastradioman@...> wrote:
Being a new to CW and and these transceivers, reading the forums I am a bit worried of damaging the unit when I get it hopefully by the end of June. First concern is powering the unit. I know it wants
DuckDuckGo did not detect any?trackers.
Being a new to CW and and these transceivers, reading the forums I am a bit worried of damaging the unit when I get it hopefully by the end of June.

First concern is powering the unit.? I know it wants 12v max, my 3Ah Bioenna battery has a nominal voltage higher than that at least when fully charged, Hans has recommended placing several diodes in series to reduce the voltage.? In trying to keep things universal and simple, I am thinking of placing a small voltage reducer to limit the output power of the battery to 12v or a bit under.;using something like this device:



I prefer to keeps my equipment uniform/universal and not having a bunch of batteries of different voltage.

Second, I recently acquired a Elecraft T1 to use with it and an IC-705.? The threads indicate that during tuning the swr could hit 10 which could still damage the QMX+ even with the protection on.? The T1 specs has min power of 0.5 watts with suggested power of 2-5 watts.? Tuning mode on the QMX+ reflects 25% or perhaps at best around 1.25 watts if the unit is putting out 5 watts.

So, I would appreciate if someone could provide some guidance into how to best power the unit and tune the antenna (EFRW).? I also have EFHW atennas, but some conditions may require the random wire version.

Andrew
 

Thanks all for your help and information.

FYI:? I received the above listed reducer from Amaz## and it allows you to lock the max voltage.? I experimented with my variable power supply and for example, when I set the reducer to 12v, adjusting the power supply above 12v leaves thee output power at 12v.? Any power supply setting below 12v reflect the same output power.? The LCD lighted display can show both in/out voltage and amps.? Now I need to create a plastic storage container to house the Bioenna battery.
 

There's a good solution hidden in the menu. First, set Protection:Tune % to something like 30% or 40%. Exit. When you need to tune, go to Hardware Tests:Tune SWR. Press once more and you will have a live display of SWR, at a safe output level.
 

No extra bits like voltage reducers or resistive bridges needed!
Andrew
 

Only reason for a voltage reducer is based on what Hans has said in the build manual regarding nominal voltage:

"Operation at more than 12V will reduce the protection safety margin available in the event of very
long key-downs, hot environment, antenna mismatch, cable faults etc. I don¡¯t recommend more
than 12V. It isn¡¯t worth pushing more just for a fraction of a dB. It is acceptable to use diodes in
series on the power line, each one will drop the voltage 0.6V or so. Beware that a 12V nominal
battery will potentially be several volts higher when fully charged"

Also, there were some thread comments regarding damaging the unit from a 19v wall transformer that had a much higher voltage (15v) than listed damaging the QMX.

So combined, issues has me a bit cautious about doing things correctly.? Plus I rather standardize my equipment, especially the cables and power supplies.

I tested the voltage output using my DMM which while my power supply was set for 13.00v input and displayed 12v output, the DMM reflected 11.96v on the set of short (8") output wires.
Andrew
 

meant 9v wall transformer
 

I agree and use variants of Dan¡¯s recommendations on my end, depending what I¡¯ve got at hand. I¡¯ve had good luck with getting the SWR tune (reduced power) function to work with small auto tuners based on the N7DCC design (e.g., BI3QWQ ¡®Antuner¡¯ redesigns ¡ª self-powered, compact, yet solid (read: slightly heavy for the size), lacking latching relays). We¡¯ll soon have a way to invoke that function more quickly.


I don¡¯t notice much (any?) reduction in total output power going below a ~30% drive SWR/Protection parameter, but it¡¯s more than enough to get a reliable tune. It¡¯s also plenty to light up the LED properly on a manual QRP tuner bridge indicator.

From what I can tell, the reduction in the QMX¡¯s output is akin to going from 100w full power on my Yeasu rig, down to 5w for tuning. That should keep you in the safe zone for a while.

Also, SWR protection kicks in very fast when transmitting into a mismatched load. Does the protection poll constantly while transmitting, or just at the point of initial key down?¡­ certainly every dit is a new transmission, just not sure what happens when going from in-tune to grossly out of tune during a long keydown (easy to test, but I haven¡¯t). I¡¯m sure I¡¯m not the only one who¡¯s had Mother Nature decide they wanted my antenna out of the air in an instant while operating portable :) ?and I think the reports of smoked finals seem to have reduced a lot since the SWR protection was implemented.?
 

I have to do much of my remote hamming with a conglomeration of equipment since I have to do it on a budget. What I do is I deploy the random wire (or whatever the antenna du jour is), set up the transmitter and tuner and whatever else I want to experiment with. When all is set up, I disconnect the xciever and insert a nano vna and tune everything up with that. If there is a problem, it will show up on the vna first and is corrected. Reconnect the xciever and you're good to go.
My 2 cents.
--
Wayne S.
KF7RCM

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