6400 sensitivity discussion

W9MO

I guess the best solution for A.J. is to vote with his feet and sell his Flex. 

Bill -VA3WTB

I would not blame him, who wants a deaf receiver as he says. First time I ever heard that complaint about the radio.

Ken - NM9P

You will always need a preamp on 10 and Six Meters. And sometimes on 12 and 15. But remember with the FLEX the preamp will have no effect upon S-Meter readings like many legacy/analog rigs which derive S-meter levels from the AGC loop.

Greg SP7QJF

David Okay Patton

Robert Lonn

Doug

Lionel

A.J. AJ2I

Thanks for the additional testing lionel. I think I'm going to keep my 6400 and just use +16 all the time. Thanks to all the people who have done additional testing and help in documenting this limitation and workaround confirmation. I'm not unhappy, just disappointed. I'm on the other end of the spectrum. I'm not a contestor, I'd rather have a more sensitive radio then a top of chart dynamic range radio. When the guy in Wallis and Futuna is 4/3 with heavy qsb on 15m, I need that extra sensitivity and lower noise floor. I dont need to worry about someone 2 kcs away. When I bought the radio I expected great performance, not just ok performance. Different tools for different purposes

Lionel

KF3F

W9HH - Steve

K0FLY

K5ROX

K5ROX

I have many radios, many pretty old and my flex 6600 will not receive a signal that my others wont, my 6600 isn't any better.  I had a 6300 and it was same.

Paul Bradbeer

Good post, Gayle. The important thing is that we're discussing different RX architectures. Flex has enough gain in the RX system to hear very low down (about -140dBm) ; the fact that you may have to use 32dB of gain to get there is irrelevant! I use my 6400M extensively on 6m weak signal, and at my quiet QTH I am using the +32dB preamp. So what? ...Nothing wrong! Paul M0CVX

A.J. AJ2I

My difficulty is running out of AGC-T when you run the preamp that high. I usually run mine about 25 when I'm at +16. But when you get to +24 or +32 you can goto 10 on the AGC-T

KF4HR

Steve

James Whiteway

Poor antennas can make a great receiver preform poorly. Good antennas can make an average receiver work well. Even to the point of overloading the radio. The better the antenna the better, to a point, any radio will receive.( and transmit) James WD5GWY

Ken - NM9P

Are you saying that your "sweet spot" where the noise just begins to drop on a quiet frequency is not reached until you move from the right all the way down to 25?  (Or 10, with +24 or +32)  On which band, and with what antenna?   

Ed Stallman

>>>with the FLEX the preamp will have no effect upon S-Meter readings like many legacy/analog rigs 
That's not true , on 6m all I do is raise the preamp gain and the s-meter lowers 'At a -8 S=Meter =1.5 , each step up in gain the S-Meter lowers until I get to a +16 @ S zero 

mikeatthebeach .

Yes, the IC-7851 is great but check the price !!!!!

Ken - NM9P

Are you talking about the S-Meter level of the SIGNAL or of the background noise?  or both?

Bill -VA3WTB

Ken, 6m is the only band were the ant gain effects both the noise floor and the S meter 

Ed Stallman

Manuel Maseda

Great post Gayle. For those that don’t know him Gayle is a highly respected retired Rockwell Collins employee.

Ken - NM9P

On my 6500, I always use the max preamp (+20 dB) for best noise factor on 6 meters.  It is standard operating procedure for any of these rigs.  

As I understand it, the standard test for whether you need the preamp (and how much you need) is to switch between your Dummy load and your antenna.  If the switch to antenna makes the noise floor rise by 8 dB or more, then your receiver noise figure (which is improved by the preamp gain) is low enough so that the signal from the antenna is overcoming the internal noise generated in the receiver.  If not, you need to add preamp.  

On lower bands the preamp is not necessary and their use only reduces the dynamic range by roughly the same amount as the excessive preamp that is being used.  

Needing to use 24 or 32 dB of preamp gain on 6 meters is not a design flaw, it is part of the system gain distribution.

Another crude way I check it, is as I move the preamp from 0 to 10 to 20 dB with the antenna connected, if the noise floor drops appreciably, I needed the gain.  If it doesn't drop more than 5-8 dB, then I may not need the extra notch.

s-meter variations is something I will need to examine.....

Ken - NM9P

Michael Wheatley

George KF2T