160M BCB Intermod

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  • Updated 4 years ago

I live about 1.5 miles from a 50KW AM broadcast station (770 khz). With my Flex 5000 I was able to enjoy image free operation (even on 160 m) by using an external filter connected to the looping in / out. Since upgrading to the 6500, I’m amazed that the filter is no longer required – NOT EVEN ONE TRACE OF ANY AM BCB DEGRADATION.

Last night I switched to 160m and was alarmed to see dozens of strong images scattered across the 160 m band. Switching in that optional filter immediately removed them, but the question was “why are they back”? I discovered that the preamp was now set to +10db (another bug)?. Changing back to my default “0FF” setting returned the 6500 back to normal operation.

Can the Flex guys explain what happened? Does the preamp remove some sort of band pass filtering? Not necessarily a problem, but I was not able to find any mention of this preamp related degradation in the owner’s manual.
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WA2SQQ

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Posted 4 years ago

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David Decoons wo2x, Elmer

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Hi Bob,

if your panadapter bandwidth is set to show frequency range out of the 160 amateur range (too wide) the internal bandpass filters are automatically switched out on receive.

Try zooming in on the panadapter to show only the 160 amateur frequency range and the crap should go away.

I'll call you later tonight

73

Dave, wo2x

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WA2SQQ

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I might be mistaken, but I believe this occurred even when zoomed in. I'll try it again this evening.
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Tim - W4TME, Customer Experience Manager

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This is an easy question to answer.  What you observed was most likely the ESD protection diode on the SCU rectifying the strong BCB signals due to a signal overload condition when the +10 dB RF preamp was enabled.

It was enabled because you had most likely enabled it when you were listening to a higher frequency band.  The FLEX-6500 has only one SCU and the RF preamp is associated with the SCU, so when you tuned the panadapter to the 160m band, the RF preamp was still enabled.  The RF preamp state is not part of the band level persistence settings since you can chose to have multiple panadapters on multiple bands at the same time.  This is by design, as the RF preamp is under positive user control and it does not change based on the frequency of one panadapter. 

The SCU has band pass filtering (preselectors) and they are enabled when the panadapter is not showing WIDE in the top right hand corner.
(Edited)
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Ken - VE5KC

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I"m still very new but slowly getting use to my 6500. I was noticing the 'wide' showing on my display from time to time.. I wasn't quite sure what it meant or why it showed up.. It was on my list of things to look up but you have answered this one,

In my case I had a second panadaptor monitoring 6 meters while I was 40 meters. So now I understand this.. any time you are receiving more than just one ham band, the band pass filter is disabled and you will see wide on the display.. 

TNX .. 73 - Ken - VE5KC
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WA2SQQ

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Noted. As I stated it's not necessarily a problem since I still have my ICE filter that can be switched in as required. In general, the 6500's received is head and shoulders above the 5000, which was itself an incredible receiver. I'm amazed on what I'm receiving down below 540 khz! So happy I can get back to my roots doing some BCB DX'ing! On that band, I'm using the Kiwa loop with the 6500.