Electronics > RF, Microwave, Ham Radio

Microwave frequency counter

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MaxFrister:
I see these sorts of meters go by on ebay occasionally.  Can anyone explain how they work?  They seem to be mechanical.

eBay auction: #http://www.ebay.com/itm/Hughes-45716H-1000-Microwave-Frequency-Wavemeter-75-to-110-GHz-WR10-Waveguide-/201535315639?hash=item2eec70deb7:g:i5MAAOSwZ8ZW2iQR

edpalmer42:
Have you ever used a grid-dip meter?  These are similar.  Connect one side to your signal source.  Connect the other side to a level meter.  Tune the counter and watch the meter.  When you tune to the input frequency, you'll see a small (1 or 2 db) dip in level on the meter.

Basically, this unit is a tuned cavity that's adjustable and has a nice calibrated scale on it.

Ed

lewis:
KF5OBS has a video on them (he's on this forum somewhere):



Krytron:
I used to work on big satellite earth stations, and we had to sweep a lot of microwave devices after repair to confirm they worked and met specs.  It was common to use a microwave sweeper signal generator, attenuators, the frequency meter, a microwave diode, and a o'scope.  If one was checking a amplifier, you would set the sweeper's output to an attenuator that was set to be equal to the gain of the amplifier being tested, and then put the frequency meter on the attenuator output, and then put the microwave diode on the attenuator output, and then take the DC output of the diode to a vertical channel on a o'scope.  The sweeper also had a sweep signal output that was sent to the o'scope horizontal channel.  The scope is operated in the X-Y mode.  The frequency meter is a cavity with a high "Q" and causes a very pronounced dip on the display.  The microwave sweeper has two frequency adjustments, a start frequency and a stop frequency.  If you were sweeping 3.7 to 4.2 Ghz, you might set the sweeper to generate 3.6 to 4.3 Ghz.  You would set the frequency meter for 3.6 Ghz and then adjust the sweeper start frequency so that the display starts on the left of the scope, and then set the frequency meter for 4.3 Ghz and adjust the sweepers stop frequency for the right side of the scope.  The scope is adjusted so the vertical sweep is centered on the scope trace.  One would use a grease pencil on the scope display to make a reference trace.  You would adjust the attenuator to -1 db and then use the grease pencil to make +1 db reference trace.  Then adjust the attenuator +1 db of the required gain and make a -1 db reference trace with the grease pencil.  You remove the attenuator and replace it with the amplifier and now you can see the gain of the amplifier across the band.  You can use the frequency meter to find the frequency where the amp drops by one DB, or to zero in on serious deviations.  HP published an application note on this setup, you can find it by searching the 'net.

Electro Fan:

--- Quote from: Krytron on March 29, 2016, 08:25:47 am ---I used to work on big satellite earth stations, and we had to sweep a lot of microwave devices after repair to confirm they worked and met specs.  It was common to use a microwave sweeper signal generator, attenuators, the frequency meter, a microwave diode, and a o'scope.  If one was checking a amplifier, you would set the sweeper's output to an attenuator that was set to be equal to the gain of the amplifier being tested, and then put the frequency meter on the attenuator output, and then put the microwave diode on the attenuator output, and then take the DC output of the diode to a vertical channel on a o'scope.  The sweeper also had a sweep signal output that was sent to the o'scope horizontal channel.  The scope is operated in the X-Y mode.  The frequency meter is a cavity with a high "Q" and causes a very pronounced dip on the display.  The microwave sweeper has two frequency adjustments, a start frequency and a stop frequency.  If you were sweeping 3.7 to 4.2 Ghz, you might set the sweeper to generate 3.6 to 4.3 Ghz.  You would set the frequency meter for 3.6 Ghz and then adjust the sweeper start frequency so that the display starts on the left of the scope, and then set the frequency meter for 4.3 Ghz and adjust the sweepers stop frequency for the right side of the scope.  The scope is adjusted so the vertical sweep is centered on the scope trace.  One would use a grease pencil on the scope display to make a reference trace.  You would adjust the attenuator to -1 db and then use the grease pencil to make +1 db reference trace.  Then adjust the attenuator +1 db of the required gain and make a -1 db reference trace with the grease pencil.  You remove the attenuator and replace it with the amplifier and now you can see the gain of the amplifier across the band.  You can use the frequency meter to find the frequency where the amp drops by one DB, or to zero in on serious deviations.  HP published an application note on this setup, you can find it by searching the 'net.

--- End quote ---

Thanks for sharing the process.
Nice use of tools and techniques to make a full solution.
Old school but effective school :)
These days we probably don't see a lot of screen captures and measurements with grease pencil markings on displays - but that part of the process can still be useful :)

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