[Lowfer] LW BCs tonite in EN90xn & recent LF bench tinkering

[jrusgrove at comcast.net]

Michael

LO LPF generally not much value with a diode ring mixer ... the diodes are being switched from full 
off to full on generating their own harmonics. There may actually be some advantage to a square wave 
LO.

I-F port diplexer is definately worth the effort.

Jay W1VD  WD2XNS  WE2XGR/2  WG2XRS/2




----- Original Message ----- 
From: "Michael Sapp" <wa3tts at verizon.net>
To: <lowfer at mailman.qth.net>
Sent: Saturday, May 03, 2014 12:53 AM
Subject: [Lowfer] LW BCs tonite in EN90xn & recent LF bench tinkering


> Hi All: Several LW BCs copied this evening, nice to see the T/A path to EU still open this 
> late.....
>
> https://www.youtube.com/watch?v=HOE5jmqgC5E&list=UUfTfag2dJYGGilPLMs0uVXw
>
>
> The LO filter is a recent add-on and looks like this....
>
> http://i1296.photobucket.com/albums/ag19/wa3tts/isotemp2_zps991e55f2.jpg
>
>
> And the diplexer looks like this....
>
> http://i1296.photobucket.com/albums/ag19/wa3tts/DIPLXR_zpsb092e34e.jpg
>
>
> I looked at the output on the HP141T SA with only the LO filter added to the mixer and the net 
> effect was to lower the 2nd harmonic 3 dB but increased
>
> some of the higher order product levels several dB ---although still 30~40 dB down from the 
> 3.0~3.5 MHz IF of the converter.  Perhaps a second
>
> diplexer for the LO would be a better alternative for mixer IMD improvement vs the LO filter, 
> since the OCXO is already -44 and -62 dB down on 2nd and 3rd harmonic output on it's own
>
> (the harmonics regenerate anyway inside the DBM).....
>
> Also interesting to look at the IF xmas tree output on the SA and see the how sideband products 
> cancelled in the DBM either side of the 2nd & 4th IF harmonics with the converter connected to the 
> antenna....
>
> http://i1296.photobucket.com/albums/ag19/wa3tts/IMG_3760_zpsfcd93207.jpg
>
>
> Sorry I did not get a image capture of the converter output on the SA yet with the diplexer 
> in-line. It did show 30dB return loss from 1.7 to 30 MHz on my MFJ-259B
>
> with the exception of being around 28 dB RL in the center of the 3.3 MHz IF passband.  Insertion 
> loss looked to be about 1/2 to 1 dB range in the IF passband .  LO filter RL was 25dB at 3.05Mhz 
> and
>
> 20dB at 3.0 MHz on the MFJ analyzer, so it still needs a slight capacitor tweek....
>
>
> Sure felt good to melt some solder after several weeks of constantly jockeying federal forms in my 
> not-so infinite "free" time.....
>
> Thanks for the bandwidth, 73  Mike, wa3tts
>
>
>
>
>
>
>
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