03-02-2022, 07:30 PM
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
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
Doug VK4ADC @ QG62LG51
http://www.vk4adc.com
This Forum is only going to be as interesting as the posts it contains.
If you have a comment or question, post it as it may trigger or answer the query in someone else's mind.
http://www.vk4adc.com
This Forum is only going to be as interesting as the posts it contains.
If you have a comment or question, post it as it may trigger or answer the query in someone else's mind.