6600M Ant RF Gain vs 6500

John K3MA · July 2023

I sold my 6500 which I used for several years and picked up a 6600M. One of the things I noticed was that the 6600M seemed to need much higher settings of Ant RF Gain in order to hear stations. I used the accepted method of increasing Ant RF Gain by one step at a time until a point was found at which no noise floor improvement was realized. At the time I did not think much about it as everything else seemed to be fine. However, after having it for about 6 months a friend sent me his 6500 in order to test it and again I noticed the difference.

Has anyone else that switched from a 6500 to a 6600M noticed the same behavior?

I have not found a situation in which I cannot hear one station on the 6600M that I can hear on the 6500. Rather I just need to run the Ant RF Gain at a higher level to bring the noise floor down below the weak signals for good copy.

AA1SS · July 2023

Yes and I have your 6500 and loving it. Next year will be an upgrade to a 6600. Currently moving so saving money for new home which we purchased with cash. 14 acre horse property. Lots of room for towers

Mike-VA3MW · July 2023

This is an interesting situation.

The only way to do a fair comparison would be to have both units on a test bench and then use a calibrated signal generator to do a comparison.

It also depends on your AGC-T settings if you are going by audio changes as that has an impact.

If you do not think your 6600M is working correctly, you might consider opening a support ticket so we can review in detail.

73

K0FLY · July 2023

The 6600 has sharper front end band pass filters which have more loss than those in the 6500. Sherwood noted this during his measurements.

From Sherwood's Test Notes -------------------------------------------------------snip----------------------------------------

NOTE: Test data for 6600M is after May 2018 PEN (Product Enhancement Notice). Due to the insertion loss of 7-pole bandpass filters on the contest bands, recommend +16 dB preamp during daytime on 80 -17 meters if in a quiet location. 15 - 6 meters may require +32dB preamp for an adequate noise floor.Tested with Alpha v. 2.2.7 software.

---------------------------------------------------------end snip---------------------------------------------------------------

I have both radios setting side by side, I run them both with zero RF gain on the HF bands ( +8 to 10 dB above 12 meters), both hear the same, the 6500 will show a slightly lower noise flow at 0 rf gain.

Hope this helps

Gayle K0FLY

Butch · July 2023

K0FLY and Sherwood's comments are correct, and this isn't first time I've heard the overall RF gain is lower on the 6600 vs the 6500 or 6700 (given the same RF gain setting). Although I would think you should be able to compensate for the lesser amount of front end gain on your 6600 by increasing the RF Gain slider.

Granted some owners might need the contesting filtering on the 6600, but certainly not all owners. It's too bad FRS didn't design the contest filtering to where it could be bypassed when is wasn't needed.

Butch, KF4HR

KD0RC · July 2023

The contest filters can be easily bypassed by opening a second panadapter on the same SCU but a different band. This will cause the "Wide" prompt to appear indicating that the filter is bypassed.

WX7Y · July 2023

The reason there is less gain is because the Filters are tighter than the 6500 or 6700.

Gain is NOT near as important on HF as better filtering on the Lower HF Frequencies and with the extra Pre-amp settings on the 6400 / 6600 the upper HF bands work fine.

6600M Ant RF Gain vs 6500

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