Sounds a bit rough but gave good repeatable results, and Jeff and I achieved similar results when testing.
So instead I moved each antenna around by hand until I found the peak amplitude, which was captured by the “max hold” function of the spectrum analyser. It’s hard to place a 17mm printed monopole in the same position as a 80cm colinear antenna as their sizes are so different. When I swapped antennas the results differed wildly in exactly the same position.
However the tripod and clamp didn’t work very well.
I fashioned a clamp on a tripod to hold the antennas: It wasn’t a very good antenna range but after some experimentation we did get surprisingly repeatable results when we compared our antennas to several control antennas. The antenna under test was placed about 6m away and a spectrum analyser used as the receiver. I used a Nanostation 2 at the transmitter, sending continuous 802.11b broadcast pings as described here. I constructed a test range in my back yard, along the lines discussed by Erwin. This is probably due to the dielectric constant of the insulation on the wire affecting the wavelength. I started with a length of 31mm (free space quarter wavelength at 2.4 GHz) but found a good SWR at 26mm. I tuned the wire monopole to a low SWR by snipping off bits of wire, 0.5mm at a time. The PCB dipole and PCB biquads don’t look so great. The 17mm and 20mm monopoles look good, close to the reference 50 ohm load and commercial off the shelf router antennas (which have sleeve dipole construction internally). Unlike Erwin I couldn’t null it down to 0V with a reference 50 ohm load but it did give indicative readings that enabled me to compare our antennas to reference antennas and determine if they had a reasonable match to 50 ohms. When tested it gave sensible results once I fitted a decent microwave detector diode. I constructed the bridge from double sided PCB and cut the microstrip (3mm wide on 1.6mm thick FR4) with a Dremel tool to save time. SWR head, microwave PCB made with a Dremel tool
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