Longwave reception of Flex6400

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Hi,

I found that longwave reception of Flex6400 is only okay with the RF gain at 0. If RF gain is increased sensitivity drops a lot but not linear with the gain. Signal meter reading also drops for example from S9+6dB to S7 , S8, S5 and S5 with RF gain changed from 0 to 32dB. The sensitivity roll off starts at about 350kHz.

73
Thomas
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Thomas Berner

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Posted 2 weeks ago

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Thomas Berner

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Hello,

Maybe someone from Flexradio can give a comment?

Additionally I would be interested in the MDS or similar sensitivity specification for the stated RX frequency range of 30kHz - 54MHz. The Hardware Reference Manual says Nothing about that.

Thank you!

73
Thomas
DF1TB
(Edited)
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Thomas Berner

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Hello,

last try here. 

Is anybody from Flexradio reading this and able send an answer?

Next stop will then be the Helpdesk or my Distributor.

73
Thomas
DF1TB
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HCampbell WB4IVF

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These responses from Flex to previous questions may also address your concerns:

https://community.flexradio.com/flexradio/topics/6700_am_sensitivity_below_1_6mhz_3khz_bw

“The FLEX-6000 series has the same sensitivity on MW as it does on the higher bands. With the preamp off, this is a -122 dBm MDS in 500 Hz. You can do the math to convert that to other bandwidths. You can also use the 20 dB preamp on MW if you have a low gain antenna. I have not measured the preamp on MW, but it will probably reducte the noise figure down there by as much as 15 db. With something like a Pixel loop, you will get great MW reception without the preamp.”

https://community.flexradio.com/flexradio/topics/s-meter-still-not-correct-on-flex6600m-with-version-2-3-9?topic-reply-list%5Bsettings%5D%5Bfilter_by%5D=all

“Most radios don't adjust for the gain in the preamp when you turn it on.  As a result, the gain makes the noise floor RISE.  This is actually not what is happening in the radio.  A preamp should lower the noise floor.  All FlexRadio transceivers account for this and so the noise floor will generally go down, like it actually does, when you enable the preamp.”  

Also, Adam Farson’s test report of the 6700 included MDS measurements:

http://www.ab4oj.com/test/reports.html

Howard

(Edited)
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Thomas Berner

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Thanks Howard,

but I am complaining about longwave recetion belowe 350kHz and it is not the noise floor that I used for the above example but a real signal from a broadcast Station on 252kHz.

73
Thomas
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Thomas Berner

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I checked Adam Farson ́s report: he measured MDS on 3.6MHZ and above only.
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N8SDR

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Thomas, I would email flex support with the question, lately I haven't sen much activity by FLEX on the community site, its just mainly consumer to consumer responses.
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HCampbell WB4IVF

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Have you tried a "factory reset" yet?
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Thomas Berner

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This I would only do if some other user tells me that his 6400/6600 is not showing this behaviour. But so far nobody took the effort. 
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N8SDR

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Thomas I'd try and see what happens here, But  I can't I have an AN broadcast station about 700 feet away and it overloads the front end . I wouldn't be able to give you any good info becuase of that.
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Thomas Berner

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Thank you, we no longer have this Problem
 in Germany, all AM broadcasters are gone since several years.
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HCampbell WB4IVF

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Took me a while to find a real signal in all the locally generated noise here.  Finally found a CW signal on 350kHz:

 @ -8dB gain, CW signal strength shows -70dBm  / S9+

@ +32dB gain, noise floor drops and CW signal strength shows -90dBm / S7+

So probably normal Flex preamp behavior at those frequencies.

(Edited)
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Thomas Berner

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Here are screenshots to show my Problem:
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Thomas Berner

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Hello again,

thanks for the help and confirmation of my observation.

For me it is quite clear that the  current Flex Series has a poor performing preamp on longwave. There is even some degradation on AM band of about 3dB at 1.5MHz, 160m seems to be okay.

73
Thomas
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Thomas Berner

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Hello,

I finally found what I was looking for in the ARRL test report on Flex6400M , available in the download area. They measured the noise floor (MDS) with -115dBm at 137kHz (no preamp) and -98dBm (+32dB preamp) and at 475kHz with -117dBm /-115dBm (0/32dB).  The preamps seem to work normal from 3.5MHz up (1.8MHz not tested).
It is a pity that nobody from Flexradio took the small effort to leave a short comment here.
Clarified for me now albeit quite disappointing result.
73
Thomas

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