Questions about the Kenwood TS-480 radios

[foojin]

The Kenwood TS-480SAT has an internal antenna tuner. Is this a suitable tuner for marine use?

Also, the TS-480HX transmits at 200w. What is the value of this? Does it make the radio more sensitive to voltage?

Cheers and thx

[plebian99]

The extra power is worthwhile having if you doing more ham operation than marine operation. With a good antenna over sea water there is not really a need for such high power.

If you going into the Polar regions where absorption of radios signals is worst compared to the tropics the extra power is helpful. Aurora absorption can make HF communications difficult and the extra power can help.

The 3db extra from the TS480HX can help you overcome other losses in your system. You have to trade off available battery storage versus the extra power. 200 watts is rarely needed for coastal marine communications or even pactor. I have a TS480HX on my boat and I rarely use it above 50 watts.

If you draw more current you drop more voltage. Your installation will have to be beefed up to minimise voltage drop. Bigger wiring will be needed or install the main box of the TS480HX as close to the battery bank as possible. You can do this with the remote head easily. If you are seriously thinking of installing a TS480HX, I would consider installing a boosting voltage regulator.

The inbuilt tuner is probably not good enough. You could however get lucky if the antennas impedance is within the matching range. This is very unlikely and most inbuilt tuners wont tune high impedance end fed antennas like backstay antennas. They also struggle with low impedance loads such as short vertical antennas like the Shakespeare whips. Even thinking along these lines is terrible engineering practice.

1. Tuning a multiband antenna through a piece of coax is a terrible and lossy option.
2.You could use a 4:1 or 9:1 UNUN at your antenna base and then use the TS480's antenna tuner. This is slightly less lossy but may work if you know your antennas impedance characteristics.
3. The better option is to use a UNUN as above at the antenna base with the antenna tuner directly at the base. Even UNUN's are not magic and cant match every possible impedance. You ideally need a multi ratio unun that matches the expected impedance.
4. The best option is to place a tuner that can match your antenna directly at the base. The losses associated with doing this is typically 1 to 3 db and no more. Option 3 above has losses above 3db and is typical as high as 6db.
5. I have done near-field measurements and antenna modeled the above scenarios and the modelling software is overly optimistic about the losses.

Always keep these losses in perspective. A 3db loss is half your power a 6db loss is even worst. Most HF radios are used for coastal communications circuits and signal strengths are strong enough where you wont even notice these losses with fading. Thats why even a crap installation "will work"

You have to do the best with what your got and within your budget. You can skin the cat with a tuner built into a radio like the TS480SAT if you know what you doing. If you dont know what you are doing use a proper random wire marine tuner.

Short answer, any tuner built into any ham radio transceiver is a marginal antenna tuner that has a limited impedance matching range like that encountered on most marine antennas. Good luck!

[foojin]

Many thanks for the detailed reply, plebian99. I learned much from it and have lots to research today.

[SoonerSailor]

Plebian99 has give you some great advice. I would not recommend the HX model for your boat, unless your power budget is liberal. I suspect, but don't know, that the greater power capability will also translate to greater power consumption than the 100 watt version even when operating at the same power levels. In any event, a 3 dB increase in transmit power you get going from 100 to 200 watts doesn't give you very much at all in terms of "punch".

As far as antenna "tuner" placement, as Plebian99 has said it is best at the base of an antenna. However, losses in a length of coax between a "tuner" and the radiator (antenna) aren't necessarily a game killer.

Lets look at a worst case scenario. Our assumptions are:
Coax - RG-8X (a boater's favorite) in a 15 foot run tuner to antena
Frequency: 18mHz ; higher frequency than usually used, higher losses too
Antenna: Your backstay, at a length of 28 feet - almost worst case for 18 mHz, will give an SWR of around 40:1

SWR losses at this frequency will be about 3.2 dB, or half your transmit power. Again, 3dB matters, but it isn't huge. Almost any other antenna length for this frequency, or any other frequency for this antenna length, will give much better results with lower loss. Use a better coax like RG-8 or LMR400 and your SWR losses will be more like 1.5 dB in the above scenario. You will still have some losses in the tuner, but fractionally less than if the tuner is at the other end of the coax (at the antenna base).

As you go to lower frequencies too, losses at a given SWR decline. For the same 40:1 SWR as in the above scenario, losses at 7 mHz would only be 0.8 dB (you would see this kind of SWR with a 66 foot long antenna - longer or somewhat shorter the SWR would be lower).

Just some things to think about. When my Icom AT-140 failed, I was able to use a manual MFJ tuner next to the M802 transceiver to get my signals out the backstay antenna. It all still worked.

Chip