Auto Tuner Help

[KM4QPE]

Hello All
As a first post this is probably a doozy.


I have over the last few weeks managed to burn out two Auto tuner/couplers. I really dont want to name the Manufacturer, but suffice. These are US made with an excellent reputation and rated at 500 watts SSB. And are eye wateringly expensive!


The problem is- I have a functioning HF install- Icom M802 to a AT140 tuner into a End fed Longwire 72” 8” oal. This is used for SailMail Weather Gribs and E-mail. Recently at a inopportune time this system failed (obvious salt water water in the AT140) I replaced that AT140.
As a redundancy measure. I have installed a TS480HX (new) and the said new Auto tuner.
The TX’s are mounted side by side and share the same RF ground and power, the Tuners are mounted side by side and share the same RF ground. To switch from system to system. The Co-ax is swapped at the TX’s and the Tuner’s and the Long wire feed is swapped at the tuner terminal. Effectively they share exactly the same Aerial
While the M802/AT140 system functions perfectly at 150 Watts. When the cabling is swapped to the TS480 and the new tuner. The Tuner (both new tuners) perform exactly as advertised. However if more that 100 watts is sent to the Tuner. One of the 4 relays in the Tuner at the final section Inductors, prior to the Aerial terminal overheats (badly) and will incinerates itself and damage the adjacent 3 relays. Both of the new tuners have done this starting at exactly the same relay both times after applying 150 Watts.
I have asked the manufacturer directly. Under exactly what circumstances can these kinds of voltages be generated? To date I have had no response. Due to time elapsed I am now doubtful that a response will be forthcoming.
Can anybody give some insight into what is actually happening here?


Thank you
Mike

[VK4ADC]

Mike

First question is what frequency(ies) is this gear operating at ??   

I realise that it won't be in the amateur bands but there are lots of marine frequencies that could be in use.
Why is this important ?   The 72ft8inch wire length (possibly including an extra length of feed wire) may be just the wrong length at the specific operating frequency such that the impedance/reactance values cause the tuner to be set into a situation where the inductors / relays are being subjected to excessive circulating RF current.

The easiest way to find out is through the use of a VNA (eg a nanoVNA) and measure the characteristics of the antenna (wire) at the feed point which normally connects to either radio/tuner.

The next step/method is to measure the SWR between the radio and the tuner and - preferably with the RF ouput power reduced - which should theoretically be below 1.5:1 once the tuner has finished tuning.  Is the relay/inductor area of the ATU still getting hot ??

The next thing to try is to measure first then add a length of wire to the "far end" of the longwire temporarily so that it alters/moves the antenna's frequency resonances a bit.  What length of wire is determined by the exact frequency in use. A quick grab of the calculator shows that the fundamental resonance of the wire as-is should be about 3.3MHz.  If perchance you are operating on/near an even multiple (6.6, 13.2, etc MHz) then your ATU is trying to match to an extremely high impedance with complex resistive and reactive components. It might not be designed to handle that.   Changing the wire length alters those characteristics to the point where the ATU can provide an easier Z match. Probably ideally alter the antenna wire length by about 5% at the specific operating frequency :   ie 5% of 75/F(in MHz), answer in metres.   If nothing else, the antenna feed Z will have changed enough to alter the internal L-C combinations to achieve a low-enough SWR match.  The permanent length change - if necessary - is your problem.

The TS480HX needs an UN-UN ( 4:1, 9:1, 16:1 etc) between the radio output and the long-wire connection to reduce the actual antenna impedance to something different/lower and within the ATU's impedance range.

The above may not be a final answer but is a starting point as to finding out why these burn-ups are occurring...

Doug

[KM4QPE]

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Hello Doug
The SailMail stations normally have about 8-10 frequencies starting at 5.0 Mhz and going up to 22 Mhz. More or less the same as WinLink.
I am perplexed here because as I outline below. This install works flawlessly with the Icom M802 and the Icom AT140.
The Aerial is the back stay for the boats Mast. It is 10mm Dia, 7/19 type, 316 stainless steel wire. Each end is insulated with a special high tensile Insulator factory made specifically for that application. The length between those insulators is 57” 10”. Attached to above the lower insulator is a 10mm2 High Voltage Silicon insulated Cable 11’ 8” long which connects to a Large ceramic thru panel RF insulator. This section of cable is “stood off” the lower un-insulated section of the SS wire Back Stay with 4” stand off insulated spacers. From that thru panel insulator to the Tuner Terminal is 3’2” straight length of the same HV 10mm2 cable. That gives the 72’ 8” radiating element. All those cable connections are crimped, soldered and heat shrunk.
The RF grounds at the TX’s and the Tuners is the boat hull. At the Tuners they are Grounded by 4” copper tapes 6” long and secured with multiple SS 6 mm bolts to the rear bulkhead. This is a fully welded water tight bulkhead and so forms a intergral part of the 63’ Aluminium Hull. At the TX’s the RF ground is 4” copper tape bolted to a rib of the hull. The Aluminium hull alone is a massive ground plane, with out considering the coupling effect to the sea water and the direct connection via 6 large sacrificial anodes.

The fact that this works is that last night (Thursday 3/02 ) I made several contacts to NSW on 10 & 12 Mhz using the Icom M802 and the AT140 @ 120Watts. Also 2 contacts to Brunei on 5 & 6 Mhz. And one contact to Belgium on 16Mhz. I am located 50 Nm South of Singapore. All the time during those connections I had in line a Diamond SX200 SWR/Power meter. SWR was always less than 1.3 there were no anomalies with reflected power. I have to concluded that the Aerial and the connections to RF Ground and the connections between TX and Tuner are good. I have no visible signs of stray RF any where in electronic aboard. All the control cables are choked with Fairite Type 31 ferrites.


To alter the length of the Aerial is not all that easy. The fixed section between the Insulators cannot be altered with out major work. The only section that I could alter as a test is the 11’ 8” between the lower insulator and the Ceramic thru panel insulator. The problem with testing and substitution is that you dont know you have a issue until the SWR starts to waver. By then you have a heat damaged relay. I will make enquiries regarding the nanoVNA. Getting stuff here is frustrating. Singapore is 50 miles away but getting shipments in is a problem.


However:-
If I connect the new out of the box TS480HX and the “inflammable Tuner” into exactly that same cabling. The tuner will tune to low SWR’s all across the 3.5 to 28 Mhz range ie nothing higher than 1.4 It retains all the tune settings, it re-tunes to preset’s instantaneously. It does not show any anomalies by the Diamond SWR/Power meter or the TS480 panel SWR. I can contact and hold contacts and transact with SailMail stations. But at 150Watts, and it seems to be in the 12-18 Hz range. The Tuner will spontaneously lose tune, SWR will start to fluctuate minimally and if you do not shut it down it will burn up the Relays in that final Inductor section. In the first failure I did not realise what was happening and it destroyed 3 of the 4 relays in that final section and blew the 2 amp onboard fuse. Once I received the second replacement “inflammable Tuner” I watched it like a hawk and as soon as I saw it waver I shut it down. That still left me with a relay (K41 by the Cct diagram) that shows visible heat deformation.
This Inflammable Tuner is rated at 500Watts PEP. It is 30% physically larger than the Icom AT140 and the Relays are at least 50% larger than those that are used in the AT140.

It is both fascinating and frustrating that the $600 AT140 (rated 150 watts) can do what the $1300 500 Watt “inflammable Tuner” cannot.

[VK4ADC]

Ok, different approach.  
 
Do you have access to a range of RF-style capacitors ??   The aim is to add a fixed capacitance directly at the unbalanced terminal of the tuner output in parallel to 'ground', changing what it sees as the effective impedance (R +- Jx) the antenna represents.  That will affect the way the Auto-ATU sets up for minimum SWR, and might change which relays are selected at the time.  A value in the range 100pF to maybe 500pF would be effective, but only if available. 

The same Z-change effect can be achieved by adding an inductance in series at the tuner out, again changing the complex Z the antenna appears as to the tuner.  
Grab a length of PVC tube (eg 40mm, 50mm) maybe 300mm long, using uninsulated copper wire with turns well-spaced apart to create an 'air-wound' inductor.  Terminate on the ends of the PVC tube.   One end goes to the antenna feed wire and a clip-lead goes from the turns to the tuner output to make a selectable-value inductance.   You could try the whole inductor as a starting point and see how it tunes, maybe move the clip lead to 3/4 then 1/2, then 1/4 of the turns while testing in each condition.   That is simply making it a slightly-loaded "longwire" but it will present a different Z at the tuner terminal, thus it will alter which internal L's and C's are in use at any given frequency.  You can always shift the clip lead to exclude any in-line inductance to go back to 'standard operation condition'.

I'm not sure what the "inflammable tuner" brand and model code is (not stated so far) but that info might be useful to find a schematic and then find those relays you mentioned. Of course it might have already sustained enough damage to be unreliable.

Your thoughts ??

Doug

[KM4QPE]

Hi Doug
As the manufacture has still not responded to or acknowledged my enquiry from more than a week ago. It seems they are no longer interested in offering any assistance.

The ATU in question is a SGC 235. – Reputedly the “Mack Truck” of all ham ATU’s. From my experience thus far. It is actually a “Dinky Toy”

What I am attempting here is a direct substitution
ie- removing a Icom AT140 from a working system and replacing it with a (supposedly far more capable and robust) SGC235 – no other changes.

At the moment I don’t have any RF Caps. I could do the inductor. But today I am pretty browned off and I am done with the whole deal. This has consumed an inordinate amount of time, energy, not to mention considerable amounts of money on something that should be almost a plug and play installation.

Yesterday I pulled the second 235 out and replaced the burnt relay by cannibalizing a working relay from the first 235 board. After replacing that faulty relay and re-installing everything. The 235 functioned. I then set the TS480 to tune at 20 Watts max. By the published specs the 235 can supposedly take up to 100 watts at Tune. I wanted to give the 235 enough power to tune & lock correctly. I put the Power SWR meter in line and went from 3.5 Mhz to 28 Mhz in 0.5Mhz steps testing the 235 against SWR. It tuned perfectly across that range with a couple of peaks. A couple of times I had to force a re-tune but each time it re-tuned with a better solution. The most pronounce peak at 26.5 Mhz was a max of 1.8 – 1. The overall performance was excellent.

I then put a contact thru to the SailMail station in NSW on 12 Mhz and uploaded a test message. (The previous SWR tests gave a SWR at 12 Mhz of 1.09 and 1.05 at 12.5 mhz) The signal strength was very low with a lot of QRM and it took a lot of time/attempts to transmit the data. During the contact the SWR did not waver. The TS480 is set to 100 watts. The link initiates at 100 watts and once established drops to ~ 50 Watts. So the 235 was doing much of it’s work at ~50 Watts. I then tried a Winlink station VK6KPS on 7 Mhz but had no response. I then tried VK6KPS again on 10 Mhz. After less than 10 seconds the SWR started to waver and I shut everything down immediately. That looked exactly like another burnt relay.
Today I took the cover off the 235. There is no apparent external heat damage on the relay K14 plastic cover. Maybe with so much practise I was able to shut it down before it burnt thru the Relay plastic cover.

At this point I think that I must accept that the SGC 235’s will not work where the Icom AT140 will.

Mike

[VK4ADC]

Mike

I finally located the datasheet on the FRM10N-1A1 relay (see PNG images below), and while it is rated at 12A for 50/60Hz, the RF capability is probably far lower. Interestingly the relays in your photo date to 2007 despite (I guess) that the tuner would be of more recent manufacture (???)

Your image #2 is telling : the longtitudinal damage line means that the contact connections and/or contacts themselves have an extremely large current flow through them thus the isolated heating points.  That current must be circulating RF current (rather than DC) at a very high magnitude to generate the heat within the relay structure. 
Image #1 simply shows mass destruction. 
 
I found a poor-quality image of the schematic of the SGC-235 in a user manual PDF but somehow I have doubts as to its accuracy : it shows 4 x 4.0uH inductors in series with relay contact sets across each inductor YET there is only one relay coil/power switching feed. That would mean it simply switches 16uH of inductance in-line to the output terminal. I can understand putting in 0uH, 4uH, 8uH, 12uH and finally 16uH to cope with different frequencies to obtain impedance matches but just either 0uH or 16uH does not make design sense.

The TS480HX has no internal tuner according to what I saw, presumably to a low-impedance/50 ohm port. Then you have the SGC-235 in line to a high impedance connection to your 'longwire'.   Can I make a suggestion :  insert a UN-UN at the output of the SGC-235, probably a 4:1 ratio or so.  The idea there is to transform the impedances reflected by the antenna at the various frequencies into a lower impedance ratio for the SGC-235 to tune into, thus it will set up it's internal LC matching values differently, maybe avoiding the high RF current condition.

Personally I use LDG autotuners but they are rated at about 100W (reliably) and I use one at a known 100W-state on FT8 on HF while portable and it continues to be reliable. I know you can use LDG tuners on Icom, Yaesu & Kenwood transceivers but don't know if they will handle the 200W near-continuous RF power of your TS480HX.  One of thuse plus an UN-UN might be an alternative - although it does not fix your current problem.

Anyway, a different thought line might trigger something that is a solution for you.

73 Doug