I recently change my antenna cable and noticed I didn’t have a dummy load (“carico fittizio”) rated for VHF/UHF, so instead of buying or borrowing I decided to make one.
I mostly do QRP: power rating isn’t really an issue, but I didn’t want to risk the RFP. I just bought a 50 ohm RFP (specifically this one) and started to make a suitable heat sink. Reading various interesting links (this, albeit not suitable for VHF, this, this, albeit that big bad red piece of wire gave him headaches raising the frequency…,as this one. This uses different (Wire bound?) resistor ). The one I loved? This video, that besides some impressive engineering also makes some measurements (I love measurements!) .
Standing on the shoulder of the giants I marched on to make my YADL (Yet Another Dummy Load).
I tried to avoid using those fat inductive wires by placing the RFP close to the BNC connector, and used coax core elsewhere. The center connection could be better, could be a microstrip, but it works.
Heatsink is an old heatsink from coolermaster with a working fan.
The fan wires comes into the box, where a ferrite ring is placed to avoid RF traveling to the PSU. The yellow wire is not used, the jack feeds 12v. I was tempted to use an insulated plastic jack panel connector, but for now I will not touch it
One could dream of more screws securing the heatsing to the box. I prefer to have some real estate to add three more RFP and get a parallel+series 50 ohm compound resistor (50||50+50||50) should I need them.
This is the finished dummy load.
And now for some measurement. I fired up the nanoVNA and calibrated a SOLT for VHF and another for UHF ham band, zeroing with the whole coax attached as I didn’t have a BNC <->sma connector.
And now some measurements. I am fairly novice with nanoVNA so it is possible that my measures are wishful thinking. I am confident they are OK, but hey, drop a note if you have any suggestion.
