Using Using a Flex 6500 to Help Align Home Brewed Filters

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  • Updated 7 months ago
Hi, no doubt many others have done this but it only just occurred to me.
I have been impressed with how easy it is to align the frequency response of a filter when connected to the receive loop on my 6500.
I wait for the band to die so there is just flat noise. Connect the filter between RX in and out, engage the loop in the antenna selection menu, adjust the visible bandwidth to a little more than the bandwidth of the filter and simply adjust the variable L's & C's in the filter to get the required response on the panadaptor.

This obviates the need for an expensive spectrum analyser with tracking generator. It enabled me to successfully align some home brewed 7 pole receive filters for 160, 80 and 40m.

IMHO it's a shame the newer radios do not have the RX loop.
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Posted 7 months ago

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Jim Gilliam

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Very interesting and innovative way of using your Flex. Thank you for sharing.

Jim, K6QE

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If you have a simple noise bridge, like
You wont have to wait for the bands to die down.
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New radios in the same price range have a RX loop.
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Len: yes that's true. Along those same lines, I developed the idea a little and used a spare tx on an adjacent band (into a dummy load of course) the resulting phase noise was more than sufficient for the purpose.

Varistor: fair comment, as do many legacy radios. What I should have said was the newer FLEX radios don't have the RX loop.

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It's definitely one reason why I won't even think about upgrading to the 6600. I use my "loop" connection for several different purposes. 6500 may have been the best Flex radio ever made.