MAT-705 PLUS ATU

BEST ATU FOR IC-705?

For the last few years I've been using the amazing ELECRAFT T1 with my IC-705. Well actually, I've been using the Elecraft with all my QRP radios and I've been extremely happy too!

My only gripe with the T1 has been the lack of an interface cable. Elecraft have been saying for years that they are making a lead for the IC-705 and it's just never materialised - annoying!

Anyway, when Icom introduced their AH-705, I thought it would be worthwhile investing in one, but at £300, I quickly changed my mind! And apart from the silly money, they're also quite big and heavy considering the application.

I'd previously looked at the Mat-705 but the first version of it was not very highly rated, so I gave it a miss. When the PLUS model was introduced, it looked to be much more interesting, so I looked further into it. It too was a bit pricey when it was launched, but I was always going to wait for one to appear on the second-hand market anyway.

MOONRAKER 

I found one on Facebook Marketplace for £100 including postage. Bargain!!

The MAT-705 PLUS brings USB-C charging to the tuner and a redesign which removes the need for an On/Off switch. The unit turns on automatically when plugged into the radio.

The unit is small, light and looks pretty robust. It is not, however, waterproof. Some people are complaining about that, but it's not something that bothers me at all - I don't work in the rain either 😂

The MAT-705 comes with a USB-C charging lead and a 3.5mm TRS interface cable. The LEDs on the faceplate are large and bright - easy enough to see in bright sunlight.

The tuner has thousands of memories, which makes tuning super fast once it has learned the antenna its connected to, but even on a fresh tune, it only takes a few seconds anyway. It's pretty quiet too (especially compared to something like an LDG Z100PLUS).

Tuning through all the bands

I've got my MAT-705 and IC-705 configured to tune on PTT which means everything is just automatic - I simply press the PTT on the mic (or the VOX button on the radio) and tuning instantly begins. It's seamless and effortless.

If I'm using my Elecraft T1, I have to make sure I'm on 5W, change mode to RTTY, press the tune button on the T1, key up and wait for a tune, then change the mode back and adjust the power (if needed). A bit of a faff.

So having played around with the MAT-705 PLUS, I have to say I am impressed! I love the compact dimensions and the integration. Some people have complained about the battery life between charges, but it's not something that bothers me too much, because I'm always careful to prepare for a day out playing radio.

I always charge things which need charging the night before and in addition to that, I'm anal enough to always carry a USB Battery Pack with me.

So in summary, I think this is a fabulous IC-705 companion and it means I can leave my Elecraft T1 in my FX-4CR case.

 

USING THE MAT 705 WITH OTHER RADIOS

Neil, G1AAD wrote to me, telling me that he’d figured out a way to use the tuner with other radios and he very kindly put together this document to explain how it’s done….

Manually using the MAT 705 Plus ATU with any radio.

There is basically a two line interface (plus ground) between the IC-705 and the Mat ATU. The Key Line and Start line.

The Key line coming out of the 705 to the Mat tuner has 3.3V on it. When connected to the Mat tuner this drops to approx. 2.7V and basically tells the Mat tuner to wake

up and power on. At the Mat tuner end this allows the Mat tuner to tell the 705 to keep the transmit on until the ATU tuning cycle has finished.

With the Mat tuner is connected it wakes up and then puts 5V on the Start line which goes back to the 705. This tells the 705 it is connected to the tuner and illuminates

the Tuner icon in the Function menu.

On transmit the 705 pulls the Start line to ground to tell the ATU to start the tuning cycle. Once the tuning cycle has started the Start line is released after approx. 1 second and goes back up to 5V. But this timing isn’t critical which is helpful for us because this starts the tune and can be done simply with a momentary push button switch.

During the tuning cycle the Key line is held low by the Mat tuner and is released high on completion which stops the 705 transmitting. The 705 tune power is also reduced for tuning.

So all we need to do is to put approx. 3.3V on the Key line to wake the Mat tuner up and manually pull the Start line down just before pressing PTT on your connected transceiver, then release the start line and wait until the tune cycle has finished. When you hear the relays stop chattering release the PTT. Remember the Mat tuner will remember frequencies so subsequent tunes could be very short.

Unlike the 705 you will not get any indication that any particular tune has not been successful. This is signalled to the 705 using a pulse on the Key line just before it goes high and TX stop. You will have to use your own connected SWR meter or transceiver display.

I chose to use a single 3.6V AA sized battery (search for 3.6v lithium aa battery on Amazon). The diode is to drop the voltage a little to match the 705 and the resistor is to

limit the current taken by the Key line again to tie with that found on the 705. The current taken down the Key line is approx. 10uA and 70uA in Tune so the battery will last a very long time. Once tuning is complete the switch can be turned off as well because the Mat tuner has latching tuning relays and full pass through on power down.

So tune procedure is :

 Connect up – reduce TX power

 Press Start - then press PTT – then release Start (after approx. 1 sec)

 Keep PTT pressed until tune cycle finishes

 Switch off if you want

RISKS and unknowns.

 I measured the current being drawn down the Key line from the 705 and chose the components below accordingly. The Start line is pulled to ground inside the 705 anyway so a momentary switch to ground is fine. So confident on the circuit and the procedure.

 The key risk as I see it is the transmit power to tune. The 705 tune protocol deliberately reduces the output power for the tune whatever the 705 transceivers power setting – you MUST remember to do this manually on your transceiver. It looks like the 705 uses less than ½ Watt to tune and then jumps up to full set power after tune. This means you would need an in-line >10dB 5W attenuator for something like the tr(u)SDX but the FX-4CR could be turned right down to a lower setting. 

There are no obviously big load resistors inside so I would definitely stick to less than ½ watt for tuning to avoid damage to the tuner. In the AH-4 ATU document there is reference to 350mW tune power which would tie with my power readings – is that relevant ? The more recent AH-705 is quite different at 5 to 10W. 

UPDATE : did some testing with my FX-4CR and it seemed to only tune and get the green LED on when I was transmitting about 1 Watt. Definitely more delving needed here then.

 And of  course then wick it up to no more than 10W once tuned.

Many thanks to Neil for this valuable information - very much appreciated!

73, Tom, M7MCQ.