Low power output on a 6400 (~60W in place of 100W)

W4AFK Bruno

Cannot get more that 60W of our remote Flex 6400 on Palomar Mountain that's ~2 years old and running 4.1.5

• Tried using SmartLink and Maestro (remote) and SmartSDR on the colocated computer
• TXing into a lab-grade 50 Ohm dummy load - VSWR 1s 1.1:1
  • Internal TUNER is bypassed
• Added an external lab-grade power meter between the radio and the load
• DC Input while in RX is 13.6 V (measured using FRSTack 4 and an external lab-grade voltmeter)
• DC Input when transmitting at "full power" drops to 13.2 V
  • Yes, we pulled and reinserted the power pole connectors
• Transmitted on 10, 12, 17, 15, 20, 40 and 75m using:
  • TUNE (scroll bar set to max)
  • CW
  • SSB (looking at peaks)

Results:

• All measurements showed a max of ~60W
• Actually showed a range between 54W and 62W depending on the band

This remote radio is being used for voice and DATA, mainly FT8/FT4 and JS8call

• Authorized club users are trained to not go over 40W for data.

Note that when I connect to my much older remote 6400 in Florida, it shows 100W with 13.2 Vdc in TX. So there is something going on with the remote 6400.

Are we missing anything or will we need to open a ticket with Flex and perhaps send the radio for repair?

KD0RC

Hi Bruno, 13.6 is too low. I would turn the power supply up to something between 14.2 and 14.5 volts. I suspect that will solve the issue.

If not, check the internal fuse to be sure that there is no corrosion or dirt on the blades.

Do you have a long power cable, or is your power cable smaller than #10 wire? These can all add up to issues like you are seeing.

W4AFK Bruno

Hi Len - Interesting as my Florida 6400 remote starts at 13.6V in RX and drops to 13.2V in TX @ 100W and it has been like this since day one (~4 years now)

The remote 6400 I am talking about as the same DC voltage drop. This was measured using FRStack 4 and a lab grade DC voltmeter at the radio DC input. When installed, we measured the same voltage differential and it was TXing 100W into a lab-grade 50-Ohm, dummy load. Now, that same Flex 6400 can't TX more than ~60W on any band into a 50-Ohm lab-grade load

Same issue into the antennas (R8 and a Palomar Engineers BAS-71) when using the radio's built-in tuner to tweak the VSWR. The load ensures that it's not a mismatch with the antenna.

The PSU is 48-to-13.6Vdc (remote repeater/radio site is all DC) and the PSU-to-Flex cable is the stock Flex cable at around 6 feet. We cleaned the PowerPole connections.

The remote radio is a one and a half hour drive up a mountain (5600 feet level) and we only go there weekends. So we are gathering things to check for our next visit.

So far, our plan is:

• Making sure that there is no current limiter that kicked on in the 48-13.6 Vdc converter
• Checking to see if we can get 14.2-14.5 Vdc output from the converter

Any other suggestions?

W4AFK Bruno

… next weekend, we plan on switching out the 48v:12v Converter/PSU and set the voltage at the PSU terminals to ~14.5 Vdc. In the meantime, the radio is working and club members are using it, but at a lower power.

John KB4DU

60 watts is down less than 3dB compared to 100 watts, less than half an S-unit.