M802/AT140 and occasional high SWR

[jonturgeon]

Hello, sorry this seems to have been discussed a lot but I am not sure it is the same issue. Our M802/AT140 will tune correctly and work perfectly some of the time. Next time it will not tune (though the indicator on the LCD says "TUNE") and will have high SWR and cutout on transmission. Odd thing is usually the first few seconds of transmit are fine. Almost like it loses the tune.

I have checked all the coax connections, we use a KISS SSB counterpoise, new GTO15 antenna feed wire, replace the control cable plug at the antenna tuner, 6 gauge wire from battery bank to SSB, tried a friends mike. Really starting to rip out my hair.

Any thoughts as to why might cause this symptom so I can try and look there, I am starting to run out of ideas.

[transmitterdan]

I think the 802 just displays SWR text message but has no actual SWR meter function. Probably the VSWR issue is there but it takes a while for it to display.

Find a ham and ask if he will bring his inline VSWR meter to the boat. Put it in line after the base unit and verify the actual VSWR. If the VSWR is really intermittent on the same channel then the control cable may have a loose connection or bad wire.

If you can't find any cause then consider disconnecting the KISS and running a 2" (50mm) strap of copper from the tuner to the nearest thru hull.

[jonturgeon]

Hi Dan, I do have a COMET CMX-1 SWR meter inline and can confirm what the Icom is telling me. You mention the control cable, can you explain a bit as to why you mentioned it? I do know the cable supplies the power to the 140 and also the signal to tune. I was under the impression that the frequency to tune tune is transmitted on the coax feed cable? Is that true? The control cable is old but I have checked both ends and they seem ok. I can also try and hunt down a copper strap (we are in Noumea, New Caledonia right now). I just had a Icom service guy onboard and he said he did not know what was going on.

[transmitterdan]

Originally Posted by jonturgeon

Hi Dan, I do have a COMET CMX-1 SWR meter inline and can confirm what the Icom is telling me. You mention the control cable, can you explain a bit as to why you mentioned it? I do know the cable supplies the power to the 140 and also the signal to tune. I was under the impression that the frequency to tune tune is transmitted on the coax feed cable? Is that true? The control cable is old but I have checked both ends and they seem ok. I can also try and hunt down a copper strap (we are in Noumea, New Caledonia right now). I just had a Icom service guy onboard and he said he did not know what was going on.

The control cable has several wires that control relays in the tuner. If one or more of those wires is intermittent then some channels will not tune correctly. Or sometimes they will tune and then later not tune because the wire is sometimes good and sometimes not. The main unit controls tuning. It transmits a low power signal on your frequency then toggles the relays in the tuner via the control wires. It looks at VSWR and remembers which relay combination gave the lowest VSWR.

If the control cable is good then my guess is that RF is leaking back on the coax from the tuner to the main unit and possibly causing the wrong relays to switch throwing the tuning off. This can happen on certain frequencies due to poor grounding of the tuner. Do you have ferrites on the control cable close to the tuner? Do you have ferrites on the coax close to the tuner?

[Auspicious]

Originally Posted by jonturgeon

Hello, sorry this seems to have been discussed a lot but I am not sure it is the same issue. Our M802/AT140 will tune correctly and work perfectly some of the time. Next time it will not tune (though the indicator on the LCD says "TUNE") and will have high SWR and cutout on transmission. Odd thing is usually the first few seconds of transmit are fine. Almost like it loses the tune.

Sorry for your troubles.

The 802 doesn't have an SWR meter per se. The foldback circuitry in the final stages of the radio (which protects the solid state amplifier from cooking itself when faced with a significant impedance mismatch) lights up the SWR indicator as part of power reduction.

Losing tune is possible but unlikely. It sounds like you have taken the right steps. Lets go through them again.

The most likely cause is a loose connection. Just about everything heats up, at least a little with use. The scenario you describe is classic loose or intermittent connection.

Lets do the easy stuff first. Disassemble the backstay connection (is that what you have), clean it, and put it back together. If a hose clamp is involved that needs to be fixed. Get back to me and I'll send you pictures of the best way I have found for that connection. If you don't have properly crimped and shrunk ring terminals that should be addressed.

Cleaning is, at a minimum, scrubbing the connections with a pencil eraser.

Same cleaning at the antenna and ground terminals of the antenna tuner.

The most likely cause of what you are seeing is the coax between the radio and the tuner. It may be a loose connection or corrosion in one (usually at the tuner) but it is very possible you have a badly terminated connector. If fishing new cable isn't too hard you'll often solve the problem most efficiently by pulling new, quality cable (8X, 213, or LMR-400) with professionally terminated connectors. If you can't pull a cable with connectors attached you really want some help putting on the connectors. The crimp type are not great. Silver-teflon is what I use. Let me know where you are and I'll help you track down someone that can help. Hams that maintain repeaters are a great resource.

You say that you replaced the control cable connector at the tuner. Did you do that yourself? How? Crimp or solder? Are you shore you got the pin-outs correct? Can you pull out the cable and ring out the pins to make sure?

In summary:

Make sure everything is properly terminated.

Clean everything.

Try again.

Explore changing the coax.

Then come back. There are second order factors we can start looking at after that like ground loops but those are much less likely than a bad connection.

Where are you?

[Auspicious]

Originally Posted by transmitterdan

The control cable has several wires that control relays in the tuner.

There are only four wires in the control cable between the radio and tuner: power, ground, tune, and key. All the relay control happens in the tuner. Power and ground are what you would expect. Tune is the signal from the radio to the tuner to try to match. Key is the signal from the tuner to the radio to send a low power RF signal to the tuner to use in trying to make a match by running through the tune algorithm and switching inductors and capacitors in and out with the relays.

The upshot is that once the tuner goes through initial tuning (you get the TUNE indicator on the 802, 710, or 700pro) the control cable is the least likely source of a problem.

[jonturgeon]

Originally Posted by Auspicious

Sorry for your troubles.

Where are you?

We are in Noumea, New Caledonia getting ready to head offshore to N.Z.

The coax is LMR-400 with gold plated connectors that I soldered on (I'll need to double check all this) but after I made the cables up I checked them all with an Ohm meter to make sure the shield and core were ok.

I do have ferrites in the control cable. None on the coax as after I changed it out to the LMR-400 mine were too small and I did not have time to order some, then I forgot... I'll put them on the "visit home" list.

I also have a spare pre-made coax that I will dig out and try in the morning. Got to run off to happy hour

[Auspicious]

Originally Posted by jonturgeon

We are in Noumea, New Caledonia getting ready to head offshore to N.Z.

A little far for a boat visit. *grin*

Ringing out the cable with an ohm meter is a good step. Sometimes when you solder on a PL-259 with an iron that isn't powerful enough (100W is a minimum for me, and 250W is better) you can distort the inner insulation and get a big impedance bump. The only way to find that is with an SWR meter and a dummy load. Still that doesn't fit with your described symptoms.

Ferrites on the coax aren't consistent with the symptoms either. High noise floor is associated with signal intrusion or a ground loop and ferrites might help with that, although a line isolator would be better. If you want a line isolator check out the T-4 at Radio Works.

I'd use your spare pre-made coax as a jumper to your SWR meter and get a better understanding of the loads your radio is seeing "looking" into the tuner.

[fairbank56]

Originally Posted by transmitterdan

The main unit controls tuning. It transmits a low power signal on your frequency then toggles the relays in the tuner via the control wires.

This is incorrect. The control cable wires do not directly operate any relays in the tuner. All that is done by microprocessor control in the tuner. The control cable wires supply power to the tuner, initiate tuner tuning via the white wire (start signal) and keys the radio in low power cw mode via the green wire (key).

The problem with the Icom setup is that it only tunes on low power. That is 10 watts delivered to the tuner and only 300 milliwatts delivered to the antenna! These tuners will routinely successfully tune with no antenna connected at all! Then you go full talk power and things change. I think the problem is most likely a faulty coax connector or faulty connection to the antenna.

Eric

[transmitterdan]

My apologies, you are correct. My radio+tuner is an older Icom model and it works the way I described. I like that way better because the radio restores the tuning for each channel so you only have to tune a channel once. When returning to that same channel later the radio "remembers" the tuning setup so you don't have to autotune all the time. I can see why Icom changed it so the tuner would work with any radio not just Icom.

I agree the problem is most likely a loose connection somewhere.

[MARC D]

When you have soldered the shield on your coax terminal, have you applied plenty of heat and tin?

The inner space of that connector should be filled with lead/tin. Needs a fair amount of heat to achieve a good connection between braided shield and connector.
Good luck,

Marc

[Auspicious]

Originally Posted by transmitterdan

My radio+tuner is an older Icom model and it works the way I described.

What do you have? The AT-140 and AT-130 and I believe the AT-120 are all controlled within the tuner. They all do remember tuning settings and respond quite quickly to a transmit signal to reset to the saved settings.

I haven't seen any Icom radios (ham or marine) that directly control the tuners. What do you have and are there manuals available online?

[fairbank56]

Originally Posted by transmitterdan

My radio+tuner is an older Icom model and it works the way I described.

Which model is that?

I like that way better because the radio restores the tuning for each channel so you only have to tune a channel once. When returning to that same channel later the radio "remembers" the tuning setup so you don't have to autotune all the time.

The AT-140 also saves the tuning setup in it's memory. The only problem being there is no backup battery, only a capacitor is used so if you don't use the radio for a couple weeks, the memory is cleared.

I can see why Icom changed it so the tuner would work with any radio not just Icom.

They don't readily work with non Icom radio's which is another downfall of Icom's tuners.

Eric

[Auspicious]

Eric - shall we start taking turns? *grin*

[jonturgeon]

Hi all, thanks for all the good info. I am going to take another look at it this morning (replace the coax again). I have another question. The odd thing I am seeing is when I transmit all seems good and low SWR, then several seconds into the transmission, I get high SWR, at that point I continue to hold the mike button down but stop talking. The radio continues to transmit with high SWR like I am still talking. If I re-tune then all is ok. Can someone explain what is happening? Funny thing is I walked around the docks and talked with other cruisers, most seem to report similar difficulty to tune (need several tries) to varying degrees.

I really need to check my connectors. I did use a high powered solder iron (pistol grip one) but my soldering skills could be better. For the shield I did the method I found on the web that soldered the shield to the outside of the connector barrel. I found it was much easier to see what was going on.

One more addition, I do have the T-4 installed right before the AT140.