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

[Pat Bunn]

I have used square waves with diode ring mixers at LO port and had good results. I believe Mini Circuits says it is a good practice. Much easier to generated higher power LO signals also. My current LF receive converter uses a +17 dBm Mini Circuits BNC mixer with a digital buffer supplying a square wave LO signal

Pat
N4LTA

Sent from my iPhone

On May 3, 2014, at 7:22 AM, <jrusgrove at comcast.net> wrote:

> 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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