Kenwood TM-V71 Issue

Discussion in 'Mobile Radio Systems' started by K3TEE, Nov 9, 2018.

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  1. K3TEE

    K3TEE Premium Subscriber QRZ Page

    Checking the RF power output on my new TM-V71A with two different power meters (Diamond SX400), I found that the max power out on both 2m and 70cm is lower than specified. I checked the power into both a dummy load and into a two-band vertical with similar results. The power output on 2m for H, M, and L are 32w, 10w and 4w. For 70cm, it's 25w, 8w, and 3w. The readings should be around 50w, 10w and 5w. Any ideas on what's causing the low readings?
  2. KA9JLM

    KA9JLM Ham Member QRZ Page

    What is your power supply voltage ?

    The voltage will affect output.
  3. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    Good point. It is not uncommon for the output power to drop to half the rated output when being battery-powered with the engine off (≈12.2 vdc). Engine running, will put the voltage around 14 vdc, with the resulting full power rating. However... If the SWR is a bit high, the output will drop.
  4. K3TEE

    K3TEE Premium Subscriber QRZ Page

  5. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

  6. HB9PJT

    HB9PJT Ham Member QRZ Page

    At the rig or at the PSU? Often the problem are the contacts of the fuse holders

    73, Peter - HB9PJT

  7. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    Good point Peter.
  8. K3TEE

    K3TEE Premium Subscriber QRZ Page

    SWR into both dummy load and my antenna are 1:1 or close to it. Initial measurements were made running the V71 off a power supply in the house set at 13.8VDC. Followup measurements were made running off a fully charged, AGM battery which yielded somewhat lower RF power output numbers. I will contact Kenwood Monday to see if they can help me resolve the issue over the phone. If not, I will have to ship the V71 to them for repair. I will let you know what happens.
  9. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    Depending on the AGM's design, the resting voltage will be from about 12.3 to about 13.2—NOT LOAD! The power cable itself, will have about .6 volt drop, under full load. Output power vs. input voltage of a solid state final (class C or AB), will NOT be linear. For example, it wouldn't be uncommon for the power out put to drop 50%, with a reduction on voltage of only 25%.

    Peter mentioned measuring the voltage at the back of the radio. That is an excellent suggestion, and you should try that before you send it back.
  10. K3TEE

    K3TEE Premium Subscriber QRZ Page

    I used a Samlex SEC1235 power supply which provides 13.8VDC up to 30A. To eliminate coax attenuation, I connected my V71, Diamond SX400 power meter, and dummy load directly together with male-to-male UHF connectors. Doing so provided identical power readings on both 2m and 70cm of 35w, 10w, and 4w. At the High power level, the V71 was drawing about 8A. The voltage drop using the supplied Kenwood power cable shouldn't be more than 0.5V. I would like to believe that the V71 is designed to provide its max rated RF output at that voltage (13.3VDC). However, maybe the VDC input voltage to the V71 must be at the maximum allowable (15.87VDC) for the RF power output to reach the max rated level of 50w. Note: the V71's input voltage is spec'ed at 13.8VDC plus or minus 15%.

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