A QRP antenna tuner for QCX Mini #qcx #antennatuner


PA1DMG
 

Hi All,
I've added an article to my blog on building a small QRP antenna tuner for the QCX mini. Also works with other QRP transceivers of course.
Here's the link: http://blog.aha.nl: building a QRP antenna tuner
If you're looking for an antenna tuner that's fairly easy to build and just works this may be the thing for you.

Regards,
Marc - PA1DMG


Mike Perry, WA4MP
 

QRP Guys offers some excellent antenna tuner and tuner/antenna combinations for only slightly more than those from China and the instructions are excellent. I know. I built their Digital Power/SWR Meter w/Dummy Load.

https://qrpguys.com/qrpguys-power-swr-dummy-load

You can download their assembly manuals to preview the steps involved.

They seem to be restocking parts, but what they sell is well worth the wait.

—Mike Perry, WA4MP

On May 6, 2022, at 5:40 pm, PA1DMG via groups.io <info@...> wrote:

Hi All,
I've added an article to my blog on building a small QRP antenna tuner for the QCX mini. Also works with other QRP transceivers of course.
Here's the link: http://blog.aha.nl: building a QRP antenna tuner
If you're looking for an antenna tuner that's fairly easy to build and just works this may be the thing for you.

Regards,
Marc - PA1DMG
_._,_._,_


ken WA2MZE
 

YUCK, a TEE network.
Yes they work in that they do transform the antenna impedance to match the transmitter.  However the Tee network acts as a high pass filter and provides NO harmonic reduction.  It also can exhibit several points of adjustment where it appears to present a good match, however it also absorbs most of the power.   If the two capacitors are identical, one way to adjust the unit is to set one at full capacitance, and the other at minimum.  Then rotate BOTH at the same time in opposite directions, in the same amount.  This causes the two capacitors to act as a single differential capacitor, and if you find a good swr null, it will be one with the least power loss.

However there are better networks.  The common L network is simple, has low loss, and performs as a low pass filter to reduce harmonics.  It also uses fewer parts.    There is also the Z match.  This uses a coupling link to a wide range tuner with a series capacitor coupling to the transmitter.  The Z match requires a fixed coil with a one or two taps and a coupling link, one dual variable cap, and one single variable cap.  Broadcast type capacitors will handle up to about 100 watts, and the miniature transistor radio type variables with plastic dialectric sheets will handle about 20 watts (good for most QRP rigs). 


On 5/6/22 18:40, PA1DMG via groups.io wrote:
Hi All,
I've added an article to my blog on building a small QRP antenna tuner for the QCX mini. Also works with other QRP transceivers of course.
Here's the link: http://blog.aha.nl: building a QRP antenna tuner
If you're looking for an antenna tuner that's fairly easy to build and just works this may be the thing for you.

Regards,
Marc - PA1DMG



Albert Tatlock's Greatest Hits - Vol 1
 

On Sat, May 7, 2022 at 12:08 AM, ken WA2MZE wrote:
YUCK, a TEE network.
Yes they work in that they do transform the antenna impedance to match the transmitter.  However the Tee network acts as a high pass filter and provides NO harmonic reduction.

So what ? The rig LPF has already sorted out the harmonics.
And beside, ANY tuning network has a Q factor, meaning that anything outside of it's
matching frequency is attenuated anyway, usually by at least 10db in the real world.


  It also can exhibit several points of adjustment where it appears to present a good match, however it also absorbs most of the power.  

Any mistuned network will lose power L, T or Pi etc if you incorrectly use values that
create a match, but have a lower Q factor (odd ball L and C values).

Your assumption that it can only occur in a T network is bollocks.


Mike Perry, WA4MP
 

You’re right about the Z match being wide-range. The price is at the high end, but I’m happy with my EMTECH ZM-2. After doing a lot of reading up on portable antennas, I opted for non-random over a half-wave end fed, in part because they can be shorter than the 65-foot length of a half-wave on forty. I’ve had good luck with lengths as short as 29 feet on forty. That is a good length to string up to a tree.

The tuning of the ZM-2 was a bit touchy until I got Nelson Antennas’s 9:1 UNUN on eBay. The combination has been a dream to tune. I display the SWR on a NanoVNA, use the left knob to move the dip onto the band and then the right knob to refine the tuning. Without the NanoVNA you can tune first by peaking the noise in the receiver and then tweaking to get a SWR-indicating LED to go out.

Here’s the lengths for non-resonant antennas.

https://www.hamuniverse.com/randomwireantennalengths.html

The QRP Guys Multi Z Tuner is also a Z match. It costs less but lacks the pretty box of the ZM-2.

—Mike Perry, WA4MP

On May 6, 2022, at 6:06 pm, ken WA2MZE <wa2mze@...> wrote:

There is also the Z match. This uses a coupling link to a wide range tuner with a series capacitor coupling to the transmitter. The Z match requires a fixed coil with a one or two taps and a coupling link, one dual variable cap, and one single variable cap. Broadcast type capacitors will handle up to about 100 watts, and the miniature transistor radio type variables with plastic dialectric sheets will handle about 20 watts (good for most QRP rigs).


Steve in Okinawa
 

Nice mods! I've also modded one - yellow core, fewer turns, extra capacitors switched in, and a 3-watt resistor in the tune bridge. Carol Milazzo's blog is also very useful. I use mine with a random wire and 9:1 unun, easy to tune on 40 through 15 without leaving my seat! JS6TMW


PA1DMG
 

Hi Mike, yes i've seen the qrpguys products as well. However, I didn't know them at the time I ordered the Chinese kit.
They're probably a lot better, but this one now works well enough to try out for a while.

Regards,
Marc - PA1DMG


Ted 2E0THH
 

I built a Z match tuner from a circuit which is almost the same as the Emtech.
It was a fun build and the component cost was very low. It also helped me better understand the theory behind it as well.
I stuffed it into a box very similar to the ones that Hans uses for the QCX+, that's an original QCX in the same box next to it. 
The AMU box also contains the QCX dummy load which I can switch in when needed.




73s Ted
2E0THH