The Long Green Tunnel: March 2022

We were in Salt Lake City for a ski trip, and decided to do a SOTA activation on our off day. The weather wasn't looking that great, so we picked an easy looking peak, View Benchmark. This mountain is in the small range that separates the Salt Lake Valley from the one to the south with Provo. We prayed that the weather would hold long enough for an activation.

Parking is just on the side of the road.

The trailhead is at the end of Deer Ridge Drive, with enough space for a dozen cars or so to parallel park. There was even a port-a-potty there. To get to the summit, just follow the main dirt road in front of you. There were a few junctions, but we were able to guess the correct direction to go: uphill. As we hiked, the snow started falling harder and harder.

Hiking up.

As we had guessed, there was no view, being in the cloud with the snow. Once we got into the activation zone we stopped at the first sheltered area to set up. We started putting up the HF antenna, but with the cold and wind decided to just do 2m. Lucky for us, we got our four contacts in a bit less than 10 minutes. It was good we had a rite in the rain notepad, since it was wet. We were cold and a bit miserable, so we didn't stick around.

Operating area.

The hike down was worse, since the wind was now blowing in our faces. The snow really stung. We managed to make a wrong turn on the way down, but realized our mistake pretty quickly. Not a good time to get lost. Back at the car we brushed off the inch or so of snow that had fallen, and blasted the heater as we drove back to the hotel.

Trailhead: End of Deer Ridge Drive.
Website: SOTA Site.
Maps: AA6XA SOTA Hikes map.
Route: Follow the main road up to the summit.
Red Tape: None. Area appears to be ok for off leash dogs too.
Video: ham_bitious YouTube

Background

During our trip to Mt Umunuhm (W6/CC-052) to test radio performance in a high RF environment, we noticed that some people could hear us better on certain radios. At the time we had no way to determine if this was because of the antenna or the radio. This question bugged us, so we decided to find out.

We decided the best way to determine how a radio/antenna combination works was to transmit and use an RF field strength meter to measure the output. (Watch the video here)

Field Strength Meter

A bit of research showed that such a meter is very simple to build, so parts were acquired. We decided to use the VK3YE schematic, which is very similar or identical to others that we came across.

The values for the capacitors and potentiometer are not critical. We used 47n at the antenna, and a 50k pot. The diodes can be any germanium type. We found some 1N34A's for cheap on eBay to use. A regular digital multimeter (DMM) in voltage mode is connected across the 10n capacitor to get the reading. Adjust the sensitivity pot to get the values into a good range. We built ours on a piece of perf board, and used an alligator clip jumper as an antenna.


Testing the meter at home.

Initial tests in the shack were good. Standing above the desk with an HT resulted in up to two volts. From across the room, there were still a few dozen millivolts on the meter.

It is important to note that this meter only gives relative field strength readings. If you don't measure the position of the potentiometer, readings made with it in different positions are not comparable. At the antenna range, once we adjusted it to get an appropriate sensitivity, we did not touch it again.

Antenna Range

Since we're hams we don't have a real antenna range, but the park down the street would work just as well. One Saturday we packed up all the radios and antennas and walked over. We picked a spot in the shade, and got set up. KN6REU volunteered to be the transmitter and AA6XA logged. The radios were on the ground, or used in a sitting position, like we do on SOTA activations. The field strength meter antenna was clipped onto the handle of the tripod we were using to film, with everything dangling, and the DMM on the ground. The tripod was about 7m away from the radios. Far field is generally considered to be three wavelengths or more, so we were measuring in the far field.


Test setup.

We started with the same radio/antenna combinations we had on Mt Umunhum. We had some trouble initially, there was nothing being registered on the meter. We're not sure exactly what the problem was, but it was likely the alligator clip not grasping well. After testing those combinations, we tried each antenna with the TH-F6a, our main SOTA HT.

Radios and Antennas

Radios tested:

Kenwood TH-F6a
Radio Shack HTX-202
Yaesu FT-817
Elecraft KX3
Baofeng UV-5r

All radios were set to their highest power (5W [3W KX3]). All testing was in the 2m band (146.505MHz).

Antennas tested:

OEM Kenwood Whip
OEM Radio Shack Whip
OEM Yaesu Long Whip

The 817 is secondhand, we did not receive the small tip with it.

OEM Baofeng Whip

This has the SMA-RP connector, and we don't have any adaptors, so this antenna could only be used with the Baofeng.

Comet HT-224 tri-band whip
RH-770 extendable dual band antenna
Arrow 2m Yagi, 3 elements
Extended Double Zepp (EDZ), homemade

We also made a ~19.5 inch "tiger tail" counterpoise to test with the whip antennas. (This is about a quarter wavelength on 2m)

Results

First, note that the meter only gives relative field strength readings. A voltage of 10 or 100 is meaningless by itself.

The first test was each antenna with the radio used on Mt Umunhum.

Radio	Antenna	Field Strength (mV)
TH-F6a	OEM Whip	1
FT-817	OEM Long Whip	4
KX3	Comet HT-224	0
KX3	Comet, no right angle	0
HTX-202	OEM whip	13
HTX-202	817 whip	11
Baofeng	OEM whip	0
Baofeng	OEM with Tail	0

Some of these were surprisingly low. The 817 was one of the best transmitters on Mt Um, but here it didn't get out as well as the 202. The zero reading for the KX3 was surprising. We thought the right-angle BNC connector we used initially might be bad, so we tried again with it removed, but this made no improvement. We were not surprised the Baofeng did so poorly here. We tried with the tail here, since we couldn't move the antenna, and it didn't help. It is possible the connector did not make a good connection here since the tiger tail was not quite wide enough to fit around the SMA.

Second, we tried each of the whip antennas with our standard SOTA HT, the Kenwood TH-F6a. Readings are in mV, without the tiger tail counterpoise and with it respectively.

	no tail	tail
RH-770	400	480
Comet	20	160
817 whip	8	320
202 whip	6	180
kenwood whip	1	130

The readings without the tail were not surprising. The RH-770 is much longer than the whips, and we expected it to do better. As expected, the performance with the tail was much improved. The jump in the 817 whip's performance is a bit suspicious. We wonder if one of the two readings is wrong. We were also surprised at how bad the OEM Kenwood whip did. Back in the shack, we put the antennas on the nanoVNA (see below). The SWR of the Kenwood was particularly bad, and we could make it jump as we flexed the antenna. It is likely broken internally.

Finally, we tried the "big" antennas, the Arrow Yagi and EDZ. Readings in mV.

Yagi towards	2200
Yagi 90deg	40
Yagi away	20
EDZ	22

By far, the Yagi was the best performer when pointed at the meter. We also tried pointing it at 90 degrees to the meter, and directly away. As expected, the value dropped a lot, showing it is in fact a directional antenna. We were surprised how low the reading for the EDZ was. We've had good luck with it on summits, and expected a higher reading. One possible issue with the EDZ is that sometimes we hang it from a tree, other times it is vertical next to the pole. Further testing could show if one mounting method is better.

Conclusions

We did not find anything earth shattering. As you'd expect, directional antennas do better, and longer antennas do better.

The best way to improve your signal appears to be the addition of a counterpoise to the HT. Even with the short and possibly broken whips, there was an order of magnitude improvement in signal strength.

We are still stumped as to why the KX3 did so poorly both in this test and the receiving test. We know the internal 2m module works, it has been used to make contacts and as an IF rig for microwave bands.


So many radios and antennas (Mt Umunhum)

ham_bitious video of the testing on YouTube.

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Appendix: nanoVNA plots

These images were captured in the shack, after the antenna range testing, so no plots for the Arrow Yagi or EDZ. We do not have an adapter for the funky Baofeng connector, so no plots there either. All the plots are from 144-148 MHz, the American 2m band. The marker is at 146.52, the US simplex calling frequency. The yellow plot is return loss LogMag (higher magnitude values better), green Smith chart (closer to the center better), blue Phase, and purple SWR (lower values better).

The whips seem very sensitive to how the nanoVNA is held, how close the hand is, etc., and the return loss could easily change a few dB. As you can see, I tried to hold it the same way each time. The Kenwood whip is definitely broken. Moving the top part around would have massive changes in return loss, e.g. from -10dB to -0.01dB. The right angle adapter that we used with the KX3 seems to be fine. The last plot is the Comet antenna with the adapter.