Emtech zm2 max watt? Data?

Hi all,

I know the web says 15w max for the zm2 but is that ssb or full 15w on data modes for example?

Anyone has a better idea?

Thanks and 73s

Hi Tasos,

I would guess it means 15w of SSB only, datamodes are full cycle modes, meaning that they use the power you give them constantly, SSB however varies based on the audio tone you produce hence it never runs at full power for long unless you whistle or send a single tone for a while!

General data mode advice for rigs at least is to run them at a max of 50% of their rated max output or you risk blowing the finals, I’d imagine this extends to ATUs and besides 7.5w of PSK31 will go further than 15w of SSB, the finely concentrated RF makes sure of that :wink:

James M0JCQ

Hi Tasos,
I think The ZM-2 tuner is a variant on the Z-Match. The 15 watts is likely to be the max safe power is independent of mode. Looking at the pics suggests the power limit is based on making sure the tuning capacitors will not break down. As they use plastic dielectric they only work until the first arc.

The single toroid might also start to saturate at higher powers, causing distress to the rig as the ATU goes out of tune on peaks. In other words the tuner is voltage limited. Some antennas might result in a lower impedance at match point and the power might be able to be raised before there is a splat. But once you have had a splat it’s a replacement job. So sure you might run 20 watts and no splat, but at some point above 15 watts with some antenna frequency combination there will be trouble.

Reading the ads the company isn’t conservative so I’d suspect that in most cases 20 w will kill the tuner. Unlike most ATU specs this one claims to have limitless possibilities. I have a Z-match and it is very good, but not absolutely perfect. Neither will the ZM-2 be. It will be very good up to 15 W.


Thank you both.

I do get the idea about full cycle and the ssb power rating and this is why im not sure about it.

I personally pushed 10w psk today and i wasnt sure if im going to damage something.
Any ideas that i can derive from the schematics or components?

First thanks Ron, I’d never push PolyVaricon caps to high power anyway but I’d never considered the failure mode. I’d never contemplated that a flash over through the dielectric would be fatal.

Tasos, PSK is not a constant envelope mode so it’s power envelope is peaky like SSB, it needs a linear amplifier to work. So you should be fine running PSK to the same power as SSB in the tuner. The duty cycle may be a little higher with PSK compared to SSB but it will be primarily the peak voltages in the tuner that will do damage and they are related to the peak power. That’s the same for SSB and PSK.

There are plenty of digital modes that have a constant power envelope and would work in fine with a class C amp such as RTTY or MFSK. It is a shame that PSK31 became so popular as it is sorts the men from the boys when it comes to setting up. It isn’t difficult to adjust the TX so that you do transmit a clean PSK signal so I often cry when I see the awful signals that some people insist on sending… far too much drive into the TX, far too much output power. If MFSK had been the default mode, badly setup systems would cause significantly fewer problems for other band users.

For those that don’t know, when setting up to send PSK, you should monitor the ALC indication when sending. ANY indication of ALC says you are driving the rig too hard and you should lower the output from the computer. You should also consider your TX final PA setup. Typical 100W amateur grade PAs run in class B and if you want to send a clean signal then, to be honest, you should not setup to transmit more than 25W. High end radios that have PAs that can be switched to 100% class A (FTDX-5000 et al.) can be run at higher outputs if you are in class A mode. Ideal if it’s cold in the shack and you want to warm it up!

Another massive thumbs up for no ALC showing when using data modes.

73 Chris M0RSF

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Hi Andy,
Capacitors designed for 250 VAC operation “self heal” after a high voltage transient hits them but dc rated capacitors, even if up to 1 kV rating fail badly in mains service. Several houses have burned down in VK due to such capacitor failure and one life was lost.
With tuning capacitors with plastic film between the plates there is no need for the more expensive “self healing” dielectric.

The failure would be something like this. The small air gap between plastic and plate has it’s breakdown voltage exceeded and a tiny arc occurs. This interacts with the plastic, causing it to char which provides a permanent path between plates. If it were self healing it melts and leaves a hole in the dielectric which is now a longer air path

In general, apply enough voltage from a low impedance source and all the smoke comes out. You can’t get it back in.