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QMX update

 

QMX update. I removed one turn from L510 and 513, 30m power improved but 20m no change. New version of T501 built and certainly helped except 20m. New version L401 built and a huge improvement, all bands in pass band except 80m where pass band is a bit too high. Currently using a Sandpiper ?MV6. Are most people running an ATU? If so, thoughts on the budget ATU-10, it does look very sensitive to antenna match, no surprise.
 

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That's good news.

Auto tuners are not a good idea with QRP rigs like the QMX, QDX etc. The tuning process goes through a number of trial settings that will give very high SWR values and may damage your radio. Better to get a manual tuner. There are a number of good ones made for QRP work and quite inexpensive as kits. I use a Kanga MTM-ATU which comes as a kit and I think prebuilt is desired.

73,
Cliff, AE5ZA



On Sep 27, 2023, at 15:44, home@... wrote:

QMX update. I removed one turn from L510 and 513, 30m power improved but 20m no change. New version of T501 built and certainly helped except 20m. New version L401 built and a huge improvement, all bands in pass band except 80m where pass band is a bit too high. Currently using a Sandpiper ?MV6. Are most people running an ATU? If so, thoughts on the budget ATU-10, it does look very sensitive to antenna match, no surprise.

 

If I may make a suggestion, try a N7VE SWR bridge. the design provides at least a measure of safety for the finals, then when your Antenna tuner is adjusted to satisfaction, switch the bridge out of circuit so your signal goes straight to the ATU and provides you (the operator) with a degree of confidence in it presenting a workable matching solution for the Radio. Worth noting that many of the kit QRP tuners have this arrangement already built in.
Just my $0.02 worth.

--
?
QRP - ?EFFICIENCY AND SKILL, NOT POWER.?
?
God Bless from Wayne Dillon - NQ0RP

Fate whispered to courageous "You cannot withstand the storm"
Courageous ?whispered back "I am the storm"
 

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Opps, that is prebuilt IF desired.

73,
Cliff, AE5ZA



On Sep 27, 2023, at 16:04, Cliff <ae5zaham@...> wrote:

That's good news.

Auto tuners are not a good idea with QRP rigs like the QMX, QDX etc. The tuning process goes through a number of trial settings that will give very high SWR values and may damage your radio. Better to get a manual tuner. There are a number of good ones made for QRP work and quite inexpensive as kits. I use a Kanga MTM-ATU which comes as a kit and I think prebuilt is desired.

73,
Cliff, AE5ZA



On Sep 27, 2023, at 15:44, home@... wrote:

QMX update. I removed one turn from L510 and 513, 30m power improved but 20m no change. New version of T501 built and certainly helped except 20m. New version L401 built and a huge improvement, all bands in pass band except 80m where pass band is a bit too high. Currently using a Sandpiper ?MV6. Are most people running an ATU? If so, thoughts on the budget ATU-10, it does look very sensitive to antenna match, no surprise.


 

I've been using a tuner for years without problems, the bs170's are more robust than you indicated, how on earth can you tune a manual tuner faster than an auto tune which takes a few milliseconds.

Paul DJ0CU G4ADF?
 

Hi Paul,

The idea is to use either a resistive bridge sensor ahead of the tuner like in this one from 4SQRP:


That limits the worst-case SWR presented to the finals while tuning.

The other option is to use a VNA to first tune the antenna and then connect the radio.? Most VNAs will not put out enough power to operate an automatic tuner.

There are also procedural steps that can be used to limit the SWR.? One example is to tune for maximum receiver noise before applying power.? This is harder on the only digital radios like the QDX.? Using the strength indicator on some of the FT8/4 software platforms is possible, but most have a slow response that makes it hard to peak the signal.

You could add an SWR indicator like this one from QRP Guys:

This can be used by either a manual or auto-tuner.? You switch in the resistive measurement and then, when tuned, bypass for full power.

The reason for the manual tuner is that most have a built-in SWR limiter that measures the SWR until tuned.? This is what is protecting the finals.? Most Auto-tuners use a Stockton bridge as the sensor that does not limit the SWR while tuning.

73
Evan
AC9TU
 

With my manual tuners, if I peak the receive noise, it's already close enough as long as the antenna's impedance is well within the range. If the noise peaking is tricky or unclear, that usually means the antenna impedance is out of the tuner's match space. I generally prefer pi-C match tuners (used in old Kenwood AT-130/AT-200 series) and Drake MN-4. A pi-C match is generally a bandpass configuration that also serves as an additional preselector and harmonic reducer, and lower loss than a Z-match and often T-match.

Once I start bringing QMX to the field regularly, I intend to build a QRP version of pi-C match tuner using polyvaricons. One thing I'm looking for is a small band selector switch (2 throw many poles for many bands). Such a slide switch exists but with small current capacity. Rotary switches are nice but they are generally bulky. Jumper pins are small and reliable until I lose pins in the field. Any good ideas?
 

I'm using an Emtech ZM-2 with a nanovna for tuning. I'm feeding a loop antenna with a balanced line (or more accurately, my entire antenna and feed system is a single length of wire) so a tuner that functions simultaneously as a balun is a good deal for me. Tuning graphically with the nanovna is pretty quick, I'd like to install an SMA connector and a switch to bring the VNA in and out of circuit rather than connecting and disconnecting coax though.
 

I use an LDG AT-600ProII auto tuner.? Before I use a QRP rig I tune up with one of my QRO rigs then switch to the QRP rig.

73, Bill NZ0T
 

On Thu, Sep 28, 2023 at 03:19 AM, Paul Harrison wrote:
how on earth can you tune a manual tuner faster than an auto tune which takes a few milliseconds.
FETs can blow in microseconds.? The problem is not the tuning time it is the bad matching solutions and transient open circuits from the relays switching which the autotuner imposes on the transmitter which cause problems.? I avoid this by using a resistive bridge between the transmitter and tuner; the loss of the bridge when in TUNE position will keep the match seen by the TX to better than 2:1.? Then switching the bridge out allows full TX power.
73, Don N2VGU

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