My plans for getting onto 24GHz have been on the drawing board for some time now. Like most people I followed the typical approach of acquiring surplus bits in the vein hope they will connect together and magically work.
My initial plans were to use modules from a 23GHz P-Comm transverter which is documented on the SBMS website. The two challenges this modification had were waveguide feeds (with a circulator) and the need for a 3GHZ IF. These complications could be overcome, but it wasn’t an elegant solution to the problem in my mind.
When the Kuhne MKU 24 G3 transveter was launched earlier this year offering 2W output and 3.5dB noise figure I decided it was a worthwhile investment. After a 3 week wait it finally arrived and being my first Kuhne purchase I was impressed with the build quality.
For the LO I used a ADF4351 based ZLPLL driving a DG0VE Ver11g5-12g5-10mW multiplier. According to the label (see pic) the multiplier required ~15mW drive between 2.3 and 2.5GHz (multiply by 5), and the website listed it as 2.875-3.125GHz (multiply by 4).
Frequency multiplication is not an exact science, as it can depend on the level and phase of the harmonics of the driving signal. When the driving device is near saturation, which is often the case from a MMIC or signal generator, it will produce some harmonics but often it is level of the harmonics that is more important than the fundamental level itself. As a result some trial and error is required to match the levels for any multiplier.
In order to find the best solution I attempted all multiplication factors in the frequency range of the ZLPLL from x3 to x8 and found that x4 mode gave the best power output from the multiplier.
The final LO lineup comprises of a ZLPLL V4 PCB with a ERA-2SM MMIC (2988MHz @ +13.3dBm) -> DG0VE Multiplier (11952 @+9.3dBm)-> Kuhne MKU 24 G3
The transverter had SMA outputs with the same spacing as most coax realys. The transverter provides a +12V output to switch the relay for transmit mode. However looking through my collection of relays all I could find was latching type. After pondering for a while I decided the best solution was to deploy my sequencer to look after the relay switching. A full sequencer was overkill but the firmware has always been hard coded making it difficult for others to use. So I have invested some time in the firmware to make it more general purpose (I’m not there yet, but moving in the right direction…)
To add some “appeal” to the project I added a Nextion LCD display which is programmed with a basic set of HMI instructions that adds a nice GUI to the front panel to show status of the transmitter, supply voltage etc. More time could have been spent adding more and more features that ultimately reduce the chances of making a contact, so I have declared the project complete for now.
Several options were explored until I finally settled on the Jaycar HB5050 diecast Aluminum box measuring 222mm x146mm x 55mm. This matches my 10GHz transverter which I expect to be used alongside this new 24GHz setup.
The master reference is a CTS OCXO that is underneath the ZLPLL in the photo. The performance of the OCXO is great – after 15 minutes warmup from a cold oven I found the frequency to be within +/- 10Hz on 24GHz. This included the TCXO reference of my FT817.
The frequency stayed within the +/- 10Hz envelope for over 2hours before I gave up and repeated the test the following night, only to fine it still on frequency.
This OCXO was previously run in for a week, which is why it performed so well.
Power output is just under 2W out on 24GHz and not having a noise source calibrated at 24GHz I could not make an accurate measurement, but could verify the front end worked.
Regretfully there are no locals on 24GHz so I now have to play the waiting game until the ZL1’s and I are able to arrange a suitable time to make a contact. Stay tuned!