6400 sensitivity discussion

A.J. AJ2I

I've always felt the 6400 reciever was lacking when it came to RX sensitivity, particularly when it comes to pulling out weak signals. Tests I've done with signal generators and the recent Sherwood report confirms this. It's the worst on the list!Using a preamp at +16 on bands above 40m is a must if you're trying to hear a weak signal. The method listed in the article below is irrelevant when it comes to the 6400. https://helpdesk.flexradio.com/hc/en-...

Paul Leach

This is disappointing news for 6400 owners. I am currently away from home ( cruise, celebrity edge - in case any fellow hams/flexors on board) I will check this out later today and read sherwood report.. 73’s Paul Gw4amz .

Stephen Hawkins NG0G

What "recent Sherwood report" are you referring to?  My 6400M seems to have no receive sensitivity problems.

A.J. AJ2I

6400 non m

Robert Lonn

[Deleted User]

A.J. AJ2I

This is regarding a 6400. Not a 6600,6700 or 6400m. A plain Jane 6400. The numbers are different for each radio. -112dBm on the noise floor. Every other radio on that list is around -124dBm with no preamp. My eagle with no preamp beats the 6400 on weak signal rx. An Icom 706 is -135! And that radio is 20 years old. Flex really dropped the ball on this.

[Deleted User]

A.J. AJ2I

I've used a signal generator and so has Sherwood. Conclusion to achieve equivalent RX of MDS vs my eagle is you need to go +16 on the 6400. Eagle does same with no preamp. -112 6400, -124 eagle. The numbers dont lie

Bill -VA3WTB

The 6400 keeps up with the very best receivers made. I would start a help desk if you feel that the receiver is not performing well for you. Perhaps Mr Sherwood tested a brocken Flex, he has done that before then published the results.

KF4HR

Craig Williams

My 6400 hears fine. Compared to my other radios. Tested with my Motorola communications test set. Hope you find your problem.

A.J. AJ2I

-112 is about what I got also. Bottom line is, you need +16 preamp to achieve the same RX compared to most other radios. That was the point of this post originally. To spread the word that you cant use the above method for determining if you need preamp. You need it period or you wont hear weak signals compared to other radios that can BECAUSE -112dBM is -112dBM is -112dBM. Which means deaf to.weak signals. Find a weak signal on 17 meters or 20 meters etc. Turn off preamp , then do same with a superhet radio and do A/B I bet the superhet will hear it and the flex wont

Joe N3HEE

AJ- Make sure the hardware updates were installed in your radio. There was an issue with heat sinks on ADC chips that caused sensitivity issues. I have 6600M with superb sensitivity on the high bands. I never need the preamp.

A.J. AJ2I

Thanks Joe. My flex shipped 5/2018. Which was supposedly after the updates were rolled out so it should be fine. I dont think there is anything wrong with the radio and its operating within spec, unfortunately just a poor spec. I think the 6400 is the black sheep of the 6000 series as it seems every other 6000 series is fine.

Bill -VA3WTB

Again, never mind the specs. A direct sampling radio receiver will out perform any superhet receiver. The 6400 is not a black sheep in the Flex radio line up and have very good receivers.

Any difference in specs you read can not be heard with the human ear, they are only lab test.

Most comments I have read is that people are very happy with the receiver. Some here have just said they find the 6400 to be just fine to them.

I will repeat. you should start a help desk. something is not right.

A.J. AJ2I

I'm not spending $150 in shipping costs to have flex tell me there is nothing wrong with my radio and its operating within spec. I will make a video with a signal generator, proving the flex hears within the published spec. I will then make a video showing the eagle hears signals the flex cannot unless you turn on the preamp to +16 which correlates to the published spec.

HCampbell WB4IVF

A.J. AJ2I

Exactly howard. The best way to get dynamic range is to make a deaf reciever. Different tools for the job. The reason I have more then 1 radio in the shack. Some are better at things then others. But the people that say a flex 6400 will hear as good as a ftdx5000 etc are just plain wrong. The proof is in the testing and the numbers.

mikeatthebeach .

Dynamic Range is great with the IC-7851 but you have to pay more for it than a SDR Rig 73 Mike

HCampbell WB4IVF

Tim - W4TME

David Okay Patton

A.J. AJ2I

Thanks for the confirmation David that I'm not insane .

Robert Lonn

Make sure your signal generator has an updated CAL sticker on it.. :-) 

David Okay Patton

Which Tim from Flex confirmed earlier in this thread: "You have to use the preamp.  There is insertion loss from the preselectors and the RF preamp is needed to overcome the insertion loss."

BTW, I'm not saying your not insane, just that you're not wrong!  :^)

Michael Wheatley

Why and how is the 6400 different from the 6400M? I hought they were the same radios except for the front panel on the M.

Art C

Well now that we’re on the subject of Test Lab Numbers.. Yesterday the results were posted and the King Flex 6700 was finally beat by the New kid on the block. The Yaesu FT-101D. Flex 6800 ??

Rich McCabe

Yea I was about to ask the same. The front panel (M) should just be a client to the rest of radio.

A.J. AJ2I

Then the M is just as deaf without a preamp

Bill -VA3WTB

Amazing considering the 6700 is around 8 years old.