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I've made a CQ-TV253 PIC controller and programmed it to command a 400 MHz signal from an ADF4351. I want to use this with my receive upconverter that I've finished [except for attenuation for LO signal] . This is a power levels question in relation to the Mike G0MJW's requirement in his article "Measure your LO power and chose suitable values for the LO attenuator so that the mixer sees 7 dBm."
I followed the good instructions in CQ-TV 259
Initially I chose -1 dBm output power. 50Ohms setting and No PAD in use. This resulted in the following trace:- -1 dBm came out as -7 dBm. I didn't fancy mixing those harmonics either. I reprogrammed the PIC for +5dBm - its highest value which gave the following result:- Minus 0.5 to 0.7 dBm.
For the upconverter circuit do I put a 0R resistor/link in for the input attenuation?
Will the upconverter work ? What did other constructors do with this project?
Here is the official advice: See the Graph on page 6 and comments on LO drive. It looks like performance of this mixer will start to drop quickly below 4 dBm drive. With 5 dBm the loss is minimal, though it won't handle strong signals quite as well.
5. LO DRIVE POWER AVAILABLE.
The LO drive is critical since the function of the LO drive is to switch the mixer diodes fully on and off for lowest distortion. So, for optimum performance, select the mixer level to match the LO drive. Mini-Circuits conveniently identifies its mixer levels by the LO drive requirement; thus a Level 7 mixer refers to a LO drive level of +7 dBm. If there are constraints on the LO power available, select the closest mixer level that is lower than the available LO power. For example, if +12 dBm LO drive is available, select a Level 10 mixer.
I put together the chain of modules pictured.
The code asks for 400 MHz at 5dBm. [Analyser levels in brackets].
The ADF4351 outputs today 405MHz and -1.6dBm [Analyser 0 dBm ref at 10dB].
Adding an amp gives 21.4dBm [25dBm ref at 40dB]
Adding 9dB attenuation gives 12.2 dB [same as before]
Adding an EBay low pass filter gives 11.75dBm pictured.
The upconverter has a 6dB attenuation fitted.
Have I understood my analyser correctly i.e. auto attenuation selected and the displayed powers are true? I hope I'm going about this ok. I'll bring the upconverter and LO units to CAT 19 South for the clinic and a tutorial.
- Spectrum at 405MHz at the LPF
- PhotoPictureResizer_191103_111613042-567x1008.jpg (234.68 KiB) Viewed 854 times
- ADF4351, club programming board, amp, attenuator and EBay LPF
- PhotoPictureResizer_191103_111530520-567x1008.jpg (250.29 KiB) Viewed 854 times
All looks sensible to me, although the ADF4351 should be on 400.000 MHz if programmed correctly. Analyser frequency calibration? You could take a look with an RTL-SDR and SDR Sharp.
I finished the project and used a pair of Mini-kits coax relays to give bypass or up conversion control.
It worked first time. Also works fine with Minitioune .
My video of the new kit in action is https://youtu.be/D9r-Zb_YhsU