#1493

[@mikesradiorepair]

Here is a trick for using "cheap" spectrum analyzers to tune duplexers and get much more dynamic range out of your instrument. Set it up as you did originally and do a rough tune to get your attenuation dip. Then set your span as narrow as you can set it or zero span of the frequency you want to notch/attenuate. Fine tune it at this very narrow span and you will see you can usually get much lower readings. Wide spans on a spectrum analyzer raise the noise floor drastically.

[@digitalradiohacker]

The problem is, now you can't see the attenuation across a wide range of frequencies, which is one of the whole points of using a spectrum analyzer. At the end of the day, these Chinese plastic boxes are a scam. What am I supposed to do with -60db dynamic range? Even an appalling duplexer will achieve -80db nulls if the screwdriver twister does their part. We have a pretty sad looking HP unit at work - I forget the model number, but it's early 90's at best. For well in excess of 3 decades, untrained chimps have been plugging just whatever they want into the front of it - You should see the N-types! No connector protectors here. It is in such a state that I won't plug anything of mine into it without intermediate patch leads to protect MY gear! With a 1GHZ span, it will still EASILY display nulls down at -80db. Don't even get me started on the Nano VNA.

[@mikesradiorepair]

@@digitalradiohacker It's actually very easy to tune a duplexer with a modern Chineseium spectrum analyzer. They have plenty of dynamic range to do the job. I can tune a duplexer on my Siglent or Rigol SA's for dips down well past -110db and when tested on my R&S 20GHz VNL vector network analyzer there is no more improvement to be had. Just takes a little longer with the SA's. Nano VNA's are another thing. They are great for the hobbyist but are useless for tuning duplexers.

[@markusberg2770]

@@digitalradiohackerUntrained chimps! What an endearing description.

[@digitalradiohacker]

@@markusberg2770 Not really. If you put enough chimps into a room with a spectrum analyzer, one of them will figure out that the connectors have a lifespan eventually. Meanwhile, most of THESE mutants have had 30 odd years to figure it out and still fall short. For this, I apologize to chimps everywhere for my gross mischaracterization.

[@pglick123]

It's either this way or that way, now I'm not sure! I'll get back to you on it.

[@amham48]

Great stuff! I've got the Siglent and for my Amateur/Ham purposes it's fine...although one can always lust!

[@byronwatkins2565]

Cavities can have very high Q. Typically, they are tuned about one bandwidth apart to broaden the observable spectrum and to increase the information rate. If you narrow the sweep, you can remove attenuation since the cavity dips there anyway and increase input power.

[@asadmarwat6445]

any idea whats the maximum wattage limit this duplexer can handle ? i intend to add a small 25 watts amp to it. will it handle 25 watts?

[@__--JY-Moe--__]

good job Abe Normal ! ;) nextime use a shop-vac !

[@andylawton2638]

Turning the -20dB attenuator off (or reducing it) on your Siglent SA when you’re measuring the duplexer will improve what you can measure to. I’ve successfully measured to -100dB tuning a duplexer with my Siglent SVA1015X which has a few dB less dynamic range than your SSA3000

[@joeteejoetee]

@1:00 THAT IS TUNED-UP GREAT !!! if those are the frequencies that you wanted...

[@davidjh7]

That duplexer really represents our times---low (quality) is high (price), and less is more. Note: I'm not reoffering to the quality of this repeater, which actually seems decent from your review.

[@RonDogInTheHouse]

Imsai, don't get me wrong, the videos is interesting and informative, but I'm always intrigued with the bits and bobs on your workbench. Are you building a copper box? Another question, what is the normal/abnormal device at the start of each of your videos?

[@IMSAIGuy]

the bits are usually from an older project, or a new project I'm working on in parallel with the present one. the 'box' will appear in the future Abnormal: kzbin.info/www/bejne/hIfKXoicmrGGodk

[@RonDogInTheHouse]

@@IMSAIGuy Don't know how I missed that video, that thing is cool, 26th week of 1970, it's smaller than I thought. Abby, Abby Normal, now that intro means soooo much more now. THANKS!

[@californiakayaker]

You must be familiar with measuring desense ?

[@jeremycyclist6269]

Very interesting and disappointing to see the dynamic range difference between the HP and Siglent. The tracking generator in the SSA3021X has (or should have) 90dB dynamic range...

[@mikesradiorepair]

The dynamic range gets lower the wider you have the span set. If he set it to a very narrow span or zero span the readings would show a much lower attenuation.

[@IMSAIGuy]

3:00

[@mikesradiorepair]

@@IMSAIGuy I'm not talking about RBW or VBW, I'm talking about frequency span. These do have a effect on dynamic range but so does frequency span. Turn on your SA and adjust nothing but the frequency span. You will see as you decrease the span the analyzer has to look at the dynamic range increases because the noise floor drops significantly.

[@IMSAIGuy]

@@mikesradiorepair yes, I did reduce the span significantly at 3:00

[@mikesradiorepair]

@@IMSAIGuy Yes but it's not like I described. Do the rough adjustment like you did and then change your center frequency to the frequency of the notch and change your span to either zero span or the narrowest span it has. The analyzer is then looking at either one frequency's amplitude over time or a very narrow (10 to 100Hz) span and sweep time is no longer a issue. Adjust it again for maximum attenuation.

[@TimPerfetto]

Thank you