Weird QRM today when I was transmitting on 20 meters

KG5PTE

I do not know where I should have posted this question. But listen to the "Weird" audio when I was transmitting this morning. We have a ham that live streams our net and I was able to go back and listen and hear myself.

Today I was on the AFFC (Air Forces flyers club net) HF 20 meter net with Commander Bob (K1BOB) . The Flex 6400 is at it again. More audio problems when I press to talk (PTT) And listen to myself over a live stream YouTube, radio event. And or over the Utah SDR. Today when I pressed the mic and transmitted on the Flex 6400, On the Alpha Delta DX LB Plus (Inverted V Dipole antenna) on Antenna Port 1. I was getting weird qrm in the back ground. when I was transmitting and talking. So I connected the Alpha Delta DX LB Plus to my Icom 7300 and transmitted on 14 MHZ (20 meters) and listened to myself over the Utah SDR site. and I sounded fine. SO I connected the 10 meter vertical antenna to the Flex 6400 on antenna port 1 and transmitted on it and I sounded fine, and even made a contact on 28.410 MHZ out west with no problems. The station said I sounded great. So why would the Flex 6400 be transmitting on antenna port 1 on the Alpha Delta with QRM but not on the Icom 7300 and then when I connect the 10 meter antenna to antenna port 1 on the Flex 6400 all is good. Relay weird.

Here is a YouTube video I made and posted on my YouTube channel: https://www.youtube.com/watch?v=XgN5YXposmw

K0FLY

Your problem appears to be frequency sensitive. Connect your Flex to a Dummy Load, TX on the bad frequency, listen to the signal on your 7300. If your TX audio is good, then you most likely you have RF getting back into your FLEX mic circuit or your station ground ground may becoming resonate at that articular frequency and the FLEX doesn't like it. If your signal is good using the dummy load and bad on an antenna then some MIX 31 Fair-rite snap cores available from DX Engineering or Pro Audio will probably fix your problem. Remember multiple turns through the snap core will increase the choking impedance by the square of the turns.

If your problem is intermittent, then it's probably a station ground problem, the moisture level in the ground is making the difference, Try getting a good ground in Saudi desert.

Snap cores on the dipole coax may also help.

My S-Lines never had RF problems, then I had to add some cores when I purchased a K3, when I replaced the K3 with a FLEX I was able to remove the of the cores. My Flex radios are located in a relay rack about six feet from my operating desk, all of the cores have been removed no problems running 1500 watts on any band. I figured that I would have some problems when I racked the radios because I was about 7 feet further from ground.

Hope this helps.

Gayle K0FLY

KG5PTE

It seems to weird to me. If it is common mode current (RFI) then it would do the same thing on the Icom 7300 using the same Alpha Delta DX LB Plus antenna on the same frequency. (14 MHZ) I tested the Flex again latter (After I re booted the radio) about an hour latter. And was getting the same audio when transmitting on 14.150 MHZ. When this started I was on 14.290 MHZ. I use the Utah Web SDR # 2 to listen to myself. I know the Flex has the capability to listen to itself. Mike Walker (VA3MW) made a YouTube video about it but I never figured out how to do this. When I switched from antenna 1 (Alpha Delta Wire) to Antenna 2 (Second 20 meter wire antenna) the problem went away. And my audio was fine. It was only doing this on antenna port number 1 on the Alpha delta antenna in my backyard,

Mike-VA3MW

Thanks for the video -- very helpful

Let me open a support ticket for you.

If you can't get FDX to work, then just listen to yourself on 20M with your 7300 with no antenna attached.

Mike

https://www.youtube.com/live/p79V9Nn8l0U?si=FJROrRDelPTU9wrz

KG5PTE

Question. When you say put a dummy load on the Antenna (In this case Antenna port 1) Should I put the dummy load right at the port feed point OR with some coax (25 or 50 feet) then put the dummy load on the end of the coax ? Also I sure this is also done with low power 20 watts or so.

Thanks

K0FLY

Put the dummy load on the radio, through a short coax jumper.

if your audio is OK on the load then I would add some split cores to you MIC cable as a first attempt to solve the problem.

As far a common mode I have seen where changing the feed line length solved the problem. The problem is still there just a different frequency. I have a choke which consists of four 2.4 inch mix 31 toroids with 10 turns of RG-8Xwound on it. This serves as a common mode choke as well as a noise choke on receive..

Gayle

KG5PTE

Ok I will run out about 25 feet of RG8 X MINI 8 to my MFJ dummy load (one gallon oil can) and put it on 100 watts (The dummy load can handle 1500) And I check it on the 20 meter phone band. As this is the frequency I was having the issue with. And transmit and listen on my Icom 7300 and my HF Antenna(s) . By the way I was on 14.290 this morning using the Alpha Delta DX LB plus on 100 Watts using the 7300 and had no audio problems. At the same time I had the Flex 6400 on my IMAX 2000 HF 10 meter vertical antenna on 28.400 MHZ on 90 watts (On antenna port 1) and heard and made two contacts on 10 meters. My audio on the Flex was fine.

KG5PTE

Update: I tested the Flex 6400 on 100 watts with 50 feet of RG 8X (Mini 8) into a one gallon can of oil. (MFJ Dummy load can) on 14.290 MHZ. and listened with my Icom 7300 and heard myself very clearly. No problems. So tonight I put an MFJ 915 RF Isolator at the radio on a one foot jumper and then connected the antenna (An Alpha Delta DX LB Plus OCF Dipole) coax to the other end. I just tested myself and listened on the Utah #2 SDR Site and could hear myself just fine. I am using the stock wired (Yaesu looking hand mic) plugged into the PTT port. And I have a a Shure Beta 58A studio microphone. That I am using now. So I use the hand mic as a foot switch and talk into the studio mic. So far no RFI and no common mode current issues.

K0FLY

Glad you got the RFI problem under control.

Gayle K0FLY

KG5PTE

I used my Iphone PTT this morning to check in on 14.290 on the Air Forces Flyers club net. Everyone said I sounded good.