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Duty cycle rating for Kenwood TS-480SAT

Discussion in 'General Technical Questions and Answers' started by AD8BU, Aug 19, 2020.

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  1. AD8BU

    AD8BU Ham Member QRZ Page

    I have a Kenwood TS-480SAT and wanted to know what the rated duty cycle is. I plan to use it while working digital modes (mostly 6 meters FT8/FT4, I have a TS-940s that I use on the other HF bands) and wanted to know if I risk frying something if I run it at 100 watts.

    I have looked over Kenwood's spec sheet for it but don't see one listed.

  2. KB0MNM

    KB0MNM Ham Member QRZ Page

    Kenwood ( ref. ) has a support section with e-mail and telephone numbers. Before you call, you should guess no more than 25% on / 75% off. A better way to solve that issue would be to add a calibrated thermal probe to the heatsink of the finals with good mechanical attachment and either the usual 'heatsink grease' or 'thermal pad'. It would be safe to say that a 100% duty cycle ( key down always ) would fry the radio finals unless extra cooling were added- it is a transceiver, which means there is a receiver in there also. While it is designed for 'digital' work, that part had more to do with emissions for AX.25 Packet (FSK/DPSK/Etc.) than what you propose... 6 meters- what sort of S.W.R. do you have?
  3. KB0MNM

    KB0MNM Ham Member QRZ Page

    See also page 91 in your user manual ( support has P/N 862-1735-50.pdf available ). If your modulation type looks more like AM than FM, your maximum should indeed be 25 watts. The minimum output is 5. Keeping the temperature of your finals under around 50 degrees C is probably mandatory. Temperature in F is measured from 32F ( freezing ) to 212F ( boiling ). That is zero centigrade to 100 centigrade. The conversion involves the ratio of 9 for F to 5 for C, with the 32 removed. ( 212-32=180; 100-0=100; 180/100 is the same as 9/5 ). Of course, you could look it up, or use a thermometer calibrated in degrees centrigrade rather than what you may be accustomed to. Maybe someone will chime in with information about the FT-8/FT-4 transmit duty cycles... and how to interrupt them for the safety of the radio.
  4. AD8BU

    AD8BU Ham Member QRZ Page

    Thank you for the suggestions on some other factors to consider.

    For those playing along at home, the manual is available here... Page 99 in that PDF file is the aforementioned page 91 in the printed version.

    In regards to temperature, that may be a decent starting point, but it doesn't specify if that temperature range is the maximum heat sink temperature, maximum ambient temperature, maximum temperature for the LCD, CPU, Finals chips, etc. Given that it is in the general section of the specifications and not for the transmitter section, I would guess that it has little to do with the finals heat output when transmitting.

    In regards to modulation, in general, digital modes are not like AM as they have a suppressed carrier, and a much narrower overall bandwidth. It has always been my understanding that AM mode offers lower output power as the radio also has to deal with transmitting both side bands as well as the carrier (though I am no engineer and could be way off the mark). FT8/FT4 would be 100% duty cycle in 15 or 7.5 second bursts, which might equate to 50% duty cycle but I don't know if the keying/unkeying of the transmitter and throwing a full load at it like that is something to take in to consideration when determining how much stress it is being put under (along the lines of the 'EBS stress test').

    I don't have a 6 meter antenna yet, I simply asked the question ahead of time so I know what I am up against when I am able to get on 6 meters.
  5. W4HWD

    W4HWD Platinum Subscriber Platinum Subscriber QRZ Page

    I wouldn’t hammer that rig in a RTTY contest, but FT8 is not the same thing as RTTY; 12.5 seconds “on” / 17.5 seconds “off” per tx/rx cycle is hardly full duty cycle.
    W4NNF, WD4ELG and AD8BU like this.
  6. KI4WCQ

    KI4WCQ Ham Member QRZ Page

    Depends on how full duty is defined. It's full duty during the TX time phase...which I beleive takes us back to the temperature issue mentioned by an earlier poster. Below is what ARRL said about duty cycle for the IC-706MKIIG. I'd guess no mention of a duty cycle means it's a lot less than 50%,

    "Most equipment does not specific duty cycle. For this reason most Product Review equipment is not subject to a specific duty cycle test. It is assumed that equipment without a duty-cycle specifications is intended for conversational use on CW or SSB."
    AD8BU likes this.
  7. W9KEY

    W9KEY XML Subscriber QRZ Page

    Funny thing about "Duty Cycle" - doesn't mean much without a bit more definition.

    For example, 1 second ON, 1 second OFF - most people would clearly think 50% DC. Maybe even 1 minute ON, 1 minute OFF. But at some point (1 hour, 1 day, 1 year) ON becomes 100%. Depends on mass of the effective heat sink and rate at which heat can be moved away (radiation, convection, conduction).

    So I tend to think of FT8 & FT4 as 50% DC, but they sure can heat up finals, versus just a good old SSB rag chew. Pays to keep an eye on the temperature readout - and it varies by frequency, too.
    W4NNF, ND6M and KP4SX like this.
  8. HB9PJT

    HB9PJT Ham Member QRZ Page

    W4HWD likes this.
  9. W4HWD

    W4HWD Platinum Subscriber Platinum Subscriber QRZ Page

    Which means it’s ok for FT8 and not overheating anything. 12.5s on every 30s would mean it’s on 41.6% of the time. During, say, a long-winded RTTY QSO, it’s “on” 100% of the time - a challenge for any transceiver.

    Even though you said 200w for 30min, 100w of RTTY would still heat it up real nice - especially since those finals are probably taking in 150w to make 100w.
  10. HB9PJT

    HB9PJT Ham Member QRZ Page

    As you can see on page 40 in the manual, the chassis gets 65 °C warm. When felt by hand, this is a very high temperature which can only be touched very briefly. With the FT8 the temperature will definitely be lower, but it still feels extremely hot.

    73, Peter - HB9PJT

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