For a non 50 ohm antennas, does the Flex receiver work well without needing a RX tuner?

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My existing Yaesu FT-991 and FT450D rigs seem to work best when the receive antenna is connected to an antenna tuner that can create a 50 ohm match, so, I have two large MFJ antenna matchers on my gear shelf. Both radios (approx) 3:1 TX antenna tuners will tune for transmit but the receive seems to suffer without an inline tuner. I currently just skip the radios tuner and use the externals. I use a 30 foot wire vertical, base inductance set for 40 meters (lots of ground radials) and a CP610 vertical. Any comments on the degradation of the Flex receive without a matched antenna? I am assuming that the Flex's internal antenna tuner/matcher only tunes on the TX path. My 6600M is a few days from arrival and I am just wanting to figure out how much space I can clear up, hopefully a lot. Thanks. de Ken K6WGX
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Ken Miller

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Posted 3 months ago

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HCampbell WB4IVF

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“I am assuming that the Flex's internal antenna tuner/matcher only tunes on the TX path.”

I believe the 6600M’s main antenna (ANT1 and ANT2) signal chain goes thru the ATU for BOTH transmit and receive (unless of course the ATU is set for bypass).   The signal chain for the receive only ports RXA and RXB does not go thru the ATU.

There’s a signal flow diagram in Section 12 of the Flex 6000 Hardware Reference Manual (available on the Flex site) that shows the architecture of the 6500 and 6700. There are differences of course, but I believe this part of the diagram applies to the 6400 and 6600 models also.


As far as using the internal vs an external tuner, I found that the internal tuner worked quite well most of the time, but occasionally does not find a match.  In that case I switched to an external tuner, making sure the internal tuner is in bypass.  Now that I have my PG XL, I use a manual external tuner, until my Tuner Genius arrives, hopefully this year.  (-:

Howard
(Edited)
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Ken Miller

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The 6400/6600 reference manual shows a little different setup. It looks like the ATU is only connected to the QSK PIN Diode switch.


I guess I'll find out how much the RX impedance matters tomorrow after I get the radio set up. I have a feeling the RX impedance will not be as critical with a SDR. Worse case I still have my tuners ;)
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HCampbell WB4IVF

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Interesting - thanks for posting the diagram.  Wonder why the change from the previous 6000 generation?  Maybe because you might not want to go thru the ATU on rx for all slices using the same ANT? I’m pretty sure they wouldn’t have made it if it was going to degrade the sensitivity of the new radios.  From what I’ve read, if needed the preamp can compensate for losses in the new BPFs.  That probably holds for the lack of ATU on ANT1/ANT2 for receive in the new radios too.  In the 6600 test reports that I’ve seen the noise and sensitivity figures with preamps engaged look pretty similar to those of the older 6ooo series, so I don’t think there’s any issue.  

Enjoy your new 6600M!

Howard


(Edited)
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Ken Miller

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I set my 6600M up this evening. This is one fine rig. When I am using my 40 meter resonate vertical, I can receive from 17 meters (and probably higher, havn't tried it) on down into the AM broadcast band with excellent results. I havn't even played with the CP610 antenna yet, other than it works great on AM broadcast band. The answer to my question is; This rig will work fine on RX with most any antenna you have, impedance seems to have very little effect. de K6WGX