Since our recent antenna analyzer “bake-off,” I purchased and built a Box73 FA-VA4 antenna analyzer kit. It was fairly easy to assemble, and so far, I’m impressed with it.
When I told my friend, Rick, KA8BMA, that I was going to try to make some measurements comparing the measurements made by the FA-VA4 to the measurements made by the Palstar ZM30, he said he’d bring over his Rig Expert AA-55 ZOOM, and we could compare all three.
My idea was to choose frequencies in the various HF bands, then adjust the antenna tuner to different complex impedances, and then make measurements with each of the analyzers. Here are the measurements we made last night:
Box73 FA-VA4 | Palstar ZM30 | Rig Expert AA-50 ZOOM | |||||||
SWR | Z | X | SWR | Z | X | SWR | Z | X | |
7100 kHz | 1.05 | 52.4 | -j0.6 | 1.0 | 49 | -j3 | 1.02 | 50.4 | **1 |
2.02 | 24.8 | -j2.6 | 2.0 | 24 | +j3 | 2.04 | 24.4 | ||
4.27 | 12.9 | -j15.4 | 4.9 | 11 | +j14 | 4.21 | 29.6 | ||
14200 kHz | 1.09 | 47.7 | -j3.9 | 1.0 | 46 | +j3 | 1.06 | 50.5 | |
2.17 | 49.7 | -j39.2 | 2.1 | 57 | +j40 | 2.1 | 62 | ||
5.24 | 150 | +j125 | **2 | 5.1 | 196 |
**1: The RigExpert didn’t indicate the reactance like the FA-VA4 or the ZM30. I wrote down some of the readings, but I’m still puzzling through them.
**2: When I started making this measurement, the ZM30 started acting flakey, as though the batteries were dead. Upon inspection, I found that one of the eight batteries had leaked, so I didn’t make this measurement.
Here are some observations:
- I think that the three meters mostly agree on SWR measurements. The Palstar seemed to be a little off when measuring SWRs around 5.0:1.
- I need to do more research on what the reactive component measurement really means. For example, look at the measurement made by the FA-VA4 at 14200 kHz and 5.0:1 SWR. The measured SWR was 5.24, but the Z is only 150. That doesn’t make sense to me.
- My test method could probably use some improvement. I was relying on adjusting my antenna tuner to generate complex impedances. It would have been better to have test loads with known complex impedances. I Googled “antenna analyzer test loads,” and the only relevant link it came up with is a page showing some load measurements for the SARK-110 Antenna Analyzer. Unfortunately, the page does not describe the loads in detail.
I know this is all kind of half-baked, and I really debated whether or not to post this, but I thought I would anyway to get some feedback. Can any of you explain the discrepancy between the Z and SWR measurements at 5.0:1 SWR?
Also, do any of you have a good suggestion for better test loads to use? I’m going to load up the Palstar with batteries again and try this experiment again once I come up with better test loads.