Sherwood's table. Most of the radios have a dedicated "RX RF amplifier" stage in front
of their mixers to help obtain sensitivity values.
Flex 6000 radios have a dedicated variable -10 dB to +32 dB amplifier stage in front of their
16 bit A to D converter, however, Flex calls this amplifier a "PRE-AMP" not a "RX amplifier".
The Flex PRE-AMP is the same as other manufacturers RX amplifier. The beauty of Flex radios is that you can set the gain that you need per band. I think that we may have gotten hung up over naming conventions.
It would be nice to know what the Rx sensitivity of other radios is with out the fixed gain
RX amplifiers. I know that the FT-5000 can be set to 0, 10 and 17 dB gain. The FT is speced at
.2 uV with 17 dB gain RX amp enabled. Flex 6400 was measured at .6 uV with 16 dB of gain.
Yeah that's down from the FT but we got +24 dB or 32 when needed.
I think that Flex is doing very good with ~-111 sensitivity, and no gain in front of the
16 bit A to D converter. Remember Sherwood measured both sensitivity and close in 3rd order IMD
with 16 dB gain in front of the A to D. (100 dB IMD isn't to shabby)
I'm happy with the sensitivity of my Flex radios.
As others have said, other factors, including IMD, filtering, dynamic range, etc., will quickly overwhelm the putative noise level differences. Radio manufacturers often "trade off" one value for another for marketing or engineering ease. It's not indicative of a "good" radio vs. a "bad" one.
Most of all, your environment affects your receive capacity. If you are experiencing noise in excess of the ITU table, don't be surprised. Noise levels have been increasing steadily in the developed world as more noise sources (switching supplies, a million kinds of devices, energy-saving lamps, etc.) that the real curves probably ought to be revised upward.
Rob Sherwood is a careful professional who provides excellent information. It is our job to read it in context and understand the very real differences between lab testing and the real world.
So after I heard the part and called the interested party, I switched on my Icom IC-9100 radio to see how it would here the station.. This is not an apples to apples comparison, but the Icom was basically useless.. I am not familiar with what other radios can do diversity like the Flex Can, you need two built in independent receivers, but I presume that when you switch to Diversity you need to Phase Lock the two receivers together, and having a 10 MHz reference input probably helps as well.. You hit the A<>B button to assure both are on the same frequency.
I was using the 6600M stand alone, not using SmartSDR external software, that should not matter much.. I think the 6600M can do this, I dont think the 6400M can do the same function as it does not have 2 SCU???
OH!!! I am still on 2.xx software, do we know if 3.xx has any enhancements to diversity reception, I know a lot of folks wanted more flexibility on how it operated..
In another thread Chuck/W9WLX provided a link to an update of the Flex article on setting preamp gain. Apologies if it’s already been discussed and is old news. In any case it's interesting and explains reasons for / differences in preamp gain settings between the Flex radios:
Why is the FLEX-6600(M) / FLEX-6400(M) noise levels +10dB higher vs. the FLEX-6500 or FLEX-6700?
Now to the difference between the FLEX-6500/FLEX-6700 and the FLEX-6600. The FLEX-6600 incorporates 7th order bandpass filters on all of the HF contest bands. The 6500/6700 incorporate 3rd order filters on those bands. The 7th order filters provide greater than 50 dB of band to band isolation between the contest bands at the cost of higher insertion loss. This is excellent for Field Day, SO2R, and other contesting configurations. This additional loss is easily compensated with additional preamp gain if required.
Let's take a look at the default preamp gain strategy for the 6400 and 6600 radios. We used the "Rural" noise floor numbers for our calculations to set the default gain for each band. Note that the 6400 filters have a lower loss on the contest bands because it uses 3rd order preselector filters on all bands just as the 6500 and 6700 do. Below you can see the ITU typical noise power in dBm in a 500 Hz bandwidth with S unit call outs in red.
Given the Rural noise floor for each band and the receiver noise for each band we calculated a the target sensitivity to be 10 dB below the ITU typical. We then picked the preamp or attenuation setting. The table below shows the gain setting and the expected MDS with no antenna attached for that setting on the respective radio. If you need more or less gain for your location, antenna and operating conditions use the procedure above to adjust accordingly.