Re: low output only on 40m



thanks for communication - I know slightly more about symptom now --

first, it likely can't be what I thought - LPF - as this LPF also is used on 30 meters!  my 30m power is okay. 

I just ran a sweep across all the bands into a dummy load -- every band except 40m is producing a lively output (my power meter is reading 10 watts on 160m * down to 4 watts on 10m -- its got a QRP scale, but it was calibrated a couple decades ago).  So I am convinced I have a substantial dip (reading less than 2 watts now on 40m). 

since I am using a dummy load - I will get some data on the width of this notch.  it is almost like a choke isn't working around 7 MHz. 

brief history: my ubitx has always been weaker on 40m.  I will confess it has one modification - an extra 45 MHz xtal filter placed on the other side of its IF amplifier.  this network made the 40m outage worse.  I saw a tip from Farhan to reduce R26 from 470 to 220 ohms to compensate for this filter loss - I made this mod.  but I can't blame it directly -- I got nice output on all other bands. 

we have 22 other ubitx from the same or recent lot in our club -- maybe mine is acting different that the population -- we are still gathering data from builders. 

the funny thing - these kind of problems always increase education, getting 'me' to examine places I would not be compelled to examine.  let's see if I can learn anything, and get this thing fixed. 

* yes I realize I have no low pass filtering of the second harmonic when operating at 1.8 MHz ... but my 160m vertical presents a dreadful match at 80m.  a nearby RBN receiver conveys I got at least 40 dB rejection by its non-report on 80m!  know your antenna before doing this - but several of us in NA operating a stock ubitx on top band. 

73 Curt

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