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I did a lot of computer modeling of the 4 bay antenna and others but I didn't learn nearly as much as I did when I was able to do some actual field testing of antennas built from the computer models.
One of the biggest mysteries I was trying to solve was some people had good luck with their DIY builds and others didn't. It appears it has mostly to do with how the elements and phase lines are mounted to the frame and what material is used for an insulator. Mounting antenna elements and phase lines directly to a wood structure appears to be a bad choice.

Range Testing
The range testing was done outside at a height of 25ft. the transmitting antenna and receiving (test) antennas were spaced several wave lengths away but not so far as to introduce ground bounce. I used a series of folded dipoles as reference antennas and all of the other measured antennas were compared to the folded dipole readings. For this test I used a spectrum analyzer with it's own tracking generator as the transmitter. Each antenna was tested at least twice to double check the readings and the same balun was used in all testing.
Field testing
The field testing was done in an open field with all antennas at a height of 20ft. The antennas were all hooked to a Channel Master CM0064 mast amp and then run through 50ft of  coax where the signal was split to a Zeinth DTT900 converter box and a B&K spectrum analyzer. I checked for the ability to lock the signal with the DTT900 and to verify what station I was receiving and used the B&K analyzer for signal readings.
One of the most interesting things I learned was that the range and field testing didn't follow the computer models as close as you might think. Most antennas
overall didn't perform as well as the computer models show and many antennas didn't show max gain at the same place as the computer models. On the flip side there were a few times where the antennas actually beat the computer models.

The 4 bay style antenna frequency response curve appears to peak at a lower frequency than the computer models show. This is not a surprise since the area where the whiskers and phase lines attach is a sensitive area and contact with most anything in that area will detune the antenna.

Here are the results of some of my range and field testing.

UHF Range testing no reflectors

This test was performed on my antenna test range
Here are the frequency curves of some DIY 4 bays, one particular note is how poorly the antenna built with wood stand-offs performed (brown plot line). The wood stand-offs were 1" x 2" wood blocks and were poly coated before the wires were attached. The exact same wires were removed from the wood frame and attached to a PVC fitting frame,  the aqua blue plot line shows the PVC frame. I then cut the whiskers to 9" as shown in the yellow dashed line plot, all these examples peak at a frequency below the computer modeled frequency. On a positive note even though the antennas built on plastic stand-offs peaked lower in frequency they did hold peak gain figures very close to the computer models.


Antenna range DIY and commercial


This test was performed on my antenna test range
This is a comparison of some DIY and commercial antennas, the 2 commercial antennas are not noted for being the best performers but the classic Channel Master CM4221 is a very popular antenna. The DIY 8 bay has a very large 52" wide angled reflector and swept forward whisker elements and 26" spacing between the 4 bay halves. The 4 bay has a 36" wide curved reflector using 2" x 4" fencing and swept forward elements.

Antenna range VHF-hi testing
This test was performed on my antenna test range
2 interesting parts of this data plot is how the CM4221 performs and how well both the DIY 4 bay and the CM4221 work with a large reflector. The stock CM4221 actually works better for VHF-hi through the screen on the lower VHF-hi channels. Adding a large reflector add about 5 db of gain to the CM4221 and has the same effect on the DIY 4 bay. I have yet to test the VHF-HI  resonator rods (NARODS) on the G-H but it's been widely reported to make a huge difference in VHF-hi performance.

PAGE 2 Field Test Data

Page 3 DIY Antenna tests