Flex 6400 - TX Audio on 15 and 20m Severely Distorted.

W4RXK

Hi Len. I ask about the mic settings as I am trying to solve a problem with phone that appears to only affect 15, 20, and 160m. This Flex 6400 is new to me as of yesterday and I have been using the IC-7300 and FTDX-10 as my primary radios. Digital modes are my current interest.

The antenna setup is a My Antenna's 80-10m fed @ the top (25 AGL) sloping downhill to a 25 foot post. RG8X coax from the antenna to an Alpha Delta 4 position switch. The second antenna is a MyAntenna 9:1 balun w/220 feet of wire. Both antennas perform as expected with reasonable SWR throughout the amateur bands. Both the IC-7300 and FTDX-10 are grounded to a large copper rod hammered into the ground. No hot RF on/near the radios or equipment that I am aware of. Occasionally, my computer monitor will have wavy lines on-screen - very slight and you have to really pay attention to see it. Nothing glaring at all. I can touch coax shield connectors when transmitting without a RFI shock.

Now onto the Flex 6400. It is connected to my laptop docking station through a 6 foot Ethernet cable. The ground cable moved from the IC-7300 to the Flex. Everything else is the same - except for the Flex. Removed the coax from the 7300 & attached it to the Flex ...

I ran through the bands doing FT8/FT4 - no issues. Made a few phone contacts on 10m - audio reports great. 15m is where the problem manifested. My calls went unanswered - many attempts to multiple very strong stations. On 20m, one operator was replying with 'I can hear a signal that is heavily distorted'; he could hear the W in my callsign, then bad hash for the rest of it. My phone signal was unintelligible. When I say bad, I mean real-bad. From the recording, you could not tell a human was speaking - only loud white noise.

My mic setting was FHM-3 default and I found the record feature. Sure enough, my voice was entirely wiped out - replaced by massive hash. Through trial and error, I found that when I turned the power down from 100w to 10w, my voice was clearer though clipping and static were present.

Changing the mic settings seemed to make a difference - slight differences. But anything over 50w on 15 & 20, my transmissions are severely degraded. DAX on or off - no difference. I played with the MIC sliders and only slight changes were heard in my recording. FHM-3 DX appears to be the least-worst of the selections. Again, really only manifesting on 15 & 20m. SWR is clean on these bands, with and without the tuner enabled. If anything, a slight touch-up when enabling the internal tuner.

Moving on to 40m and 100w - perfect. Clean as it should be - 80m too. 20m is more affected than 15m and the other bands are seemingly ok.

A friend has a 6600 and we went through his TX and microphone settings - mine match his exactly. I changed the settings, disabling BIAS and other microphone settings. This had an impact, but did not solve.

So here we are ... as a new Flex owner, I am trying to solve this problem.

My guess is RFI, but from what and where? The IC-7300, FTDX-10, and even my old TS-440 do not exhibit any has on 15 & 20m, only the Flex. Perhaps it is not the MIC settings but something else.

I reset the radio using the published process. Power off, disconnect from power, wait, power on, observe white button, continue ...

Looking for the community to help solve this.

W4RXK

Images of the firmware & mic settings.

W4RXK

Another one

KD0RC

One thing to consider is not daisy-chaining your station ground from one radio to another. This can cause a ground loop which may or may not be band dependent. A separate ground wire should be run for the Flex.

Another possibility is overdriving the mic input. Make sure that your mic level is set so that the level meter never goes red. It is the peak value (little square indicator), not the average that you are concerned with.

If it is not either of these, then it is likely RF getting in. In my shack, it was getting into my network and computer. Once I put ferrites on my USB and Ethernet cables, everything was fine.

W4RXK

The Flex is the only radio connected to the ground - I moved it from the Icom to the Flex.

John KB4DU

This sounds like it might be RF on the Mike cord or something similar. Maybe someone has a fix. Ferrites are a possibility.

Arnold Goldman

i had a clicky clicky setup on my new 8600M with the 629 mike not the handheld; RF chokes took care of the problem