VHF SOTA Antenna Tests
A perpetual ham radio question is always which antenna is best? I have several different antennas and antenna configurations for working VHF SOTA and decided to do some comparisons.
To test out some of our 2m SOTA antennas, Joyce/K0JJW and I went to Eagle Rock (W0C/SP-113) with an elevation of 9710 feet. I did the radio operating while Joyce collected the data. Eagle Rock pokes up out of South Park, which is a broad, high plain in central Colorado. This summit is kind of “mid-range” for Colorado…not as high as the 14ers but with significant elevation and prominence (~500 feet). It also was close enough to a number of SOTA chasers so I could get some good S-meter readings to compare antennas. On the summit, there is a clear 360-degree horizon, dropping off quickly in all directions.
Antenna A is our GO-TO antenna for VHF SOTA is the 3-element Yagi from Arrow Antenna, handheld so the boom is about 5 feet off the ground. Arrow does not specify the gain on this antenna but it has been measured at the Central States VHF Society conference to be ~6dBd.
Antenna B is a dual-band J-pole manufactured by N9TAX, supported by a telescoping fishing pole commonly used by SOTA activators. A J-pole has a halfwave radiator, so the gain is about 0 dBd, the same as a dipole.
Antenna C is an RH770 telescopic antenna mounted on a monopod, using a bracket that I made. See VHF/UHF Omni Antenna for SOTA Use. This antenna is a halfwave on 2 meters, so again we’d expect the gain to be ~0 dBd. The antenna is supported by a monopod which I usually just stick into the ground or strap to a bush.
The three antennas being tested were driven with short coaxial cables fitting with BNC connectors for easy changes. The transceiver was a Yaesu FT-90 powered by a small Bioenno battery.
I put the word out that I’d be doing some antenna comparisons and five chasers showed up to assist. (There were are few other chasers that were too close to Eagle Rock such that the S meter readings would have all been “full scale” and not useful.)
Most of these stations were not line-of-sight because there is mountainous terrain blocking the direct path. This makes for a good test because this is often the situation when doing SOTA activations in Colorado. We often have mountains in the way, even on the high summits. Said another way, line of sight contacts are easy-peasy and the antenna performance is not critical. Getting the signal to punch through or around mountains is when the antenna really matters.
WZ0N was line-of-sight from Eagle Rock. KN0MAP was not line-of-sight and he had his Yagi antenna pointed at Pikes Peak (away from Eagle Rock). This is a common technique on VHF…point at a high summit and hope you get enough of a reflection to make the contact. The chasers are listed below.
|W0BV||Icom IC-2730, X200A antenna, 35 watts||42 miles, blocked by a ridge|
|AD0WB||Kenwood TH72A, X300A antenna, 5 watts||39 miles, blocked by mountains|
|KN0MAP||Yaesu FT-857, 10-element Yagi pointed at Pikes Peak||35 miles, reflecting off Pikes Peak|
|WZ0N||Baofeng HT, 5 watts||29 miles, Direct line of sight|
|K0MGL||Yaesu FT-8900, 1/4-wave ground plane antenna, 10 watts||32 miles, blocked by mountains|
Your typical FM VHF/UHF radio doesn’t have a real S meter, just a bar graph display, so we worked in terms of “number of bars”. This does not give us a calibrated measurement but it does provide for a valid comparison. A signal that is 5 bars is stronger than one with 3 bars, but we don’t really know how much better (in terms of dB or S units). We recorded meter readings at both ends of the radio contact. My Yaesu FT-90 meter has 7 bars as full scale. On transmit, I was running the FT-90 at 20 watts.
|Callsign||Report Sent by K0NR||Report Received by K0NR||Report Sent by K0NR||Report Received by K0NR||Report Sent by K0NR||Report Received by K0NR|
|AD0WB||5||Full scale||3||Full scale, a little noisy||4||Full scale|
|K0MGL||7||6||1||1, very noisy||1||0, very noisy|
A quick look at the Antenna A column shows that the Yagi had consistently better signal levels than the other two antennas. For each contact, I did point the Yagi in the direction of the strongest signal, taking care to maximize the signal. This is an advantage and disadvantage…you have to point the antenna but you do get a stronger signal.
The two omnidirectional antennas (B and C) did not require pointing and they performed about the same. My impression is that Antenna B had slightly better overall performance based on listening to the FM noise. But note that the AD0WB readings were slightly better with Antenna C.
As is very common in the mountains, we experienced multipath distortion. This occurs when the signal takes multiple paths to the other station (reflecting off mountains) and then recombines at the receiver creating distortion and variation in signal level. Small changes in antenna position can cause a change in the signal level and amount of distortion. Multipath distortion was much more noticeable on the omnidirectional antennas. The Yagi antenna exhibited multipath but at a much-reduced level. This is a well-known phenomenon: directional antennas reduce multipath effects.
Another factor that I believe is important is that Eagle Rock pokes up quite dramatically compared to the surrounding terrain. Compare this to a large, flat summit that could shadow your signal at some angle of radiation. Antenna height relative to the immediate summit terrain might be more important. Another factor is that Eagle Rock is pretty much granite and not very conductive. So there is not much difference between having an antenna 5 feet off the ground (rock) vs putting it up on a mast.
Previously, I wrote about Charlie/NJ7V’s video that compared a roll-up J-pole with a 3-element Arrow Yagi antenna on two meters. Charlie’s results were a bit different, indicating that the J-pole was about the same or in some cases better than the Yagi.
The Yagi antenna clearly outperformed the two other antennas. So the Arrow 2m Yagi will continue to be our antenna of choice.
The paths to K0MGL and KN0MAP were the most difficult and this is where the Yagi performance really came through. For KN0MAP, we were both pointed at Pikes Peak and working off the reflection. This method worked well with the Yagi but had significant signal loss such that the omni antennas could not make it. Working K0MGL on the omni antennas was not much better but we did squeak out two contacts.
I was a bit surprised that Antenna B did not do significantly better than Antenna C, due to antenna height. This all seems to indicate that once you are on top of a rocky SOTA summit, additional antenna height does not matter. (It would be interesting to do some experiments with the same antenna set at different heights.) I do like having an omni antenna available so that we can monitor in all directions while eating lunch, etc. If we only have the Yagi at lunch time, it is usually laying on the ground or stuck into a tree, certainly not effective in all directions. Antenna C is so easy to deploy, it will probably be my preferred omnidirectional antenna.
This is just one test and one set of results. It will be interesting to do some further comparisons from other locations. Thanks to the chasers for assisting with these tests.
73 Bob K0NR
Test data in Excel spreadsheet: Antenna comparisons – 2m FM Eagle Rock
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I’ve had a HF dipole on the ground on a rocky (Yorkshire Grit) summit in dry conditions and found contact signal was still strong. It’s as if the summit wasn’t there and I had an antenna about 600m up in the air!
I’m told that when things get wet, signals completely change. This is most notable for mobile phone users in the area.
How well does the Arrow pack down? Is it easy to put in a backpack?