Kuhne G3 Ext Ref level

The Kuhne MKU xx G3 432 transverter modules have inbuilt OCXOs LOs (Oven Compensated Crystal Oscillator Local Oscillators), and whilst very good, they can be locked to an external 10 MHz reference from a GPS Disciplined Oscillator (GPSDO), such as a Trimble ThunderBolt.

Kuhne quote +10dBm as the minimum level for the 10 MHz feed, but what is the real minimum level required?

To determine this minimum level, I used the following;

  • 10 MHz @ +12dBm from a Trimble Thunderbolt GPSDO, fed via a DEMI 10-4 Splitter/amp
  • Windfreak SynthNV signal generator, locked with the GPSDO
  • a number of small value DC-GHZ rated SMA attenuators

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Without taking the covers off, it’s easy to determine when the G3’s internal OCXO locks to the external reference, by listening to a known (ie; locked) signal source.

(And if you do take the top cover off, you will find a “Lock” LED inside.)

If we tune to carrier frequency – 1 kHz on USB, we expect to hear a 1000 Hz beat note.

When the OCXO is free running (ie; not locked), the 1 kHz beat note may be found some kHz away instead, depending on how close the OCXO was set.

So, the Windfreak SynthNV was locked with the ThunderBolt and tuned to 1920 MHz (3rd harmonic is 5760 MHz)

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Above: Windfreak SynthNV set to 1920 MHz, in low output power mode (ideal for front end testing)

 

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Above: SynthNV locked to GPSDO, pipe cap filter on output allows us to pick off the 3rd harmonic, and remove the 1920 fundamental

 

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Above: IF rig (432 MHz IF) tuned to receive a 1 kHz beat note

 

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Above: 10 MHz into the 5.7 GHz G3 module, via the attenuator ladder

 

The various attenuators (values available: 2dB, 3dB, 4dB, 5dB) could be arranged to provide attenuation of 2dB – 14dB in 1 dB steps.

Once the minimum value of 10 MHz was found for the MKU 57 G3 432, the exercise was repeated for the MKU 10 G3 432 module.

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Above: SynthNV running on 3456 through a 10 GHz pipe-cap filter, so that a clean 10368 signal is presented to the front end

 

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Above: 10 MHz into the 10 GHz G3 module, via the attenuator ladder

 

And what was the end result?

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Both of these 5.7 and 10G G3 modules required a minimum of +0.5dBm each.
So based on the results and to allow for headroom, I would suggest a minimum 10 MHz level of +3dBm for a Kuhne G3 transverter module.

 

As Iain VK5ZD also found (+4dBm), the Kuhne specification of +10dBm appears to build in a substantial safety margin!

 

If you recall, I had +12dBm available, and the Kuhne spec only required +10dBm.
Why would I bother looking into this, in the first place?

Well, it means I can feed the 10 MHz to two Kuhne modules at once, with only a simple (cheap!) T-piece split.

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With a simple split like this, I’d expect a 3dB drop in level, with +9dBm appearing at each Kuhne module… no problems!

🙂