Interference RFI from Airband to 2 meter Flex-6500

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  • Updated 3 years ago
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Hello Flexers.
I am proud new owner of a Flex 6500.
My setup is a Flex 6500, Steppir 2 elements with 40m antenna. Also using Elecraft XV144 for 2 meter work.
I am very happy wt the radio. the receiver is super and i can tailor my TX and RX to my please.
I use it daily for DX and feel the difference from my previous radio Icom 7600.

Here is an overview of my situation:

I live within less a mile of a powerful airband transmitter on 126.700Mhz.

When I listen with Elecraft XV144 transverter  with a hustler vertical on 144-146Mhz  I was hearing a distorted signal filling the whole band. After many days of searching for the audio I found the source which was a FM commercial radio on 106.1 MHz.

Thought was to buy a FM band notch filter .... glad i didnt !! You may wonder why.

I noticed that the interference is like short transmission the qso type, so i thought to check the airband for RFI.

You can see the results with the simple experiment in the following YouTube video. It will explain better than words:

So the problem is a Receiver Intermodulation from a powerful transmitter with mixing product of a FM commercial station.
Solution was a DCI-146-4H Band pass filter and now the 144Mhz band is crystal clear !

This is a classical example of using Flex radio to demonstrate RFI as an analyzer. SUCCESS!

2ND Problem:

I hear a lot of static and crashes on HF. Can be seen on the following video , look at the horizontal lines on the waterfall. IT can be very annoying and strong esp. at humid nights with +20db crahes and noise:

I thought its the same transmitter or one of the others present on airband but it is hard to associate.
to solve the problem I used a Low band pass filter from Bencher YA 1-30Mhz. to block the upper frequencies , but that didnt improve. I also thought it is from AM band and i used a MW block filter but also no improvement.

by the the way my is grounded and also station is grounded separately. all connections have ferite beads.

Any thoughts are wellcomed.


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Mohamed Al-Bufalasa

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Posted 3 years ago

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Photo of George Molnar, KF2T

George Molnar, KF2T, Elmer

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I had similar experiences with the Elecraft transverter, and the same solution. The HF noise appears to be lightning static, which is by nature broadband and unfortunately not something any filter will remove. Suspect it gets worse the lower in frequency you go?
Photo of Ross - K9COX

Ross - K9COX

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Concur, when the noise floor rises abruptly (even a small amount) from distant lightening crashes you will see those horizontal lines. I am seeing this as we speak.
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Mohamed Al-Bufalasa

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Hi George 

Thanks for the feedback.
Yes the clicks and cracks on HF increase in intensity if I go to lower frequencies.
And yes it may be lightening far away that night. It seems much less last night.

73 de A92GR