New Project falling together
Well, I checked EMRFD out from the library a few weeks ago. I hoped it would spark some interest. It did.
As an aside, if you are a homebrewer and don't have access to Experimental Methods in Radio Frequency Design you should get access to the book. It is a great book to read and I hope to build out of.
One of the first projects recommended in EMRFD is an RF power meter. It will help with the question, "Is this thing doing anything?" I haven't had one. I have the power meter in my antenna tuner, but normally I have used a NORCAL dummy load with a DVM or my trusty Simpson meter. But the "required hand count" goes up steeply with each probe that needs to be held in place. Pretty awkward.
As I was reading the section on power meters again, I realized that the only thing I use my dummy load for is testing circuits. So why not just build it into an enclosure and include a voltmeter in the box. Then I can just plug in my circuit and the meter just sits there telling me how many watts and providing a load. No hands required. Cool!
Well to keep this story short, I spent last night at my newly cleaned bench picking parts out of the parts bin to produce a power meter. Here is the list pf parts.
- The dummy load from NORCAL provides the 50 ohm load and has the peak detector on it. It also has a mountable BNC jack that adequately mounts the whole thing. The peak detector and dummy load is good for 1-10W in short bursts.
- The meter is a 0-50uA meter I got from my dad. It is brand new in the box.
- A couple of 1.5M ohm resistors in parallel give ~750 k Ohms of resistance in series with the meter to provide a roughly 0-36V volt meter.
- The plastic Hammond case was a surplus hand-me-down from a friend at a testing lab.
Calibration: It will be as accurate as my K2. I intend to plug my K2 into it and energize with varying power levels. Then I will probably just mark the meter face at 1/2 watt intervals.
So when I mount everything I will have a 1-10W power meter that is in a small (but big enough) box to stand on the bench while I am tinkering.
The box will also have emough room to put in a more sensitive milliW meter circuit that reuses the meter at a later date. That will take a little more soldering. I haven't decided whether to just do another uncompensated meter or use something like my compensated RF probe, but that will come later.
So stay tuned and I will get some photos up when it is done.