Bandwith and isolation of preselectors and ADC overload of 6700 for SO2R

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  • Updated 1 year ago
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In my remote contest station I have a tower with a 3 el 40 m yagi (DIS 7-3) which is  no more than 70 feet from aan other tower with  5 over 5 el 20/15 m stack (JK 2015). Unfortunately I discovered that the 3 el 40 has broad resonances at  16,6 and 22,5 MHZ (< 1.4:1) which couples strongly to 20 and 15 m bands of   JK20/15 yagi. Of course putting in band pass filters and stubs could diminish these artifacts a 60 dB + 25 dB = 85 dB but still produce considerable signals into either 40 m or 20 m ham bands of the 6700. 
I understand that the preselector add 20 db of isolation per ham band. How broad are these filters per ham band? How are the RX inputs (A and B) protected?
I have read about the ADC overload indicator with the protection relay- has this function been improved anyway?     
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Kari Gustafsson SM0HRP, Elmer

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Posted 1 year ago

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Craig K9CT

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Hi Kari

You should be ok with the filters. I assume you are considering full duplex and SO2R operation. Here is the isolation sheet for calculating the isolation.

http://www.flexradio.com/downloads/fl...

Low power filters between between the radio and amplifier are needed. High power if you are concerned about the level of harmonic content. Amplifiers contribute significantly to the harmonic content and you must consider this as well.

Good luck

73, Craig K9CT
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Kari Gustafsson SM0HRP, Elmer

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Thanks Craig. It will be good advice along the road. I will be having both low power and high power filters to get some good isolation despite some extra half a dB of insertion loss.
See you in the CQ WW 160 contest! GL.