How Far on VHF SOTA?
Adam/K6ARK recently posted this video of his 2m SOTA activation in California. Adam does a really nice job with his videos and this one is no exception. During this activation, he worked KE9AJ in Arizona at 256 miles. This was an FM QSO, with KE9AJ running 6 watts and K6ARK running over 120 watts.
In the video, he shows the 8-element 2m Yagi antenna, which has a clever folding boom design (homebrew, I assume). You’ll notice that he is carrying quite a bit of gear in his pack, including a 160w amplifier, a Yaesu FT-857, several batteries, the Yagi antenna, and antenna masts. Adam has posted other videos of VHF SOTA activity, so check out his YouTube channel for them.
Note that at 256 miles, this is definitely propagation beyond line of sight. We’ve talked about this before: The Myth of VHF Line-Of-Sight.
This has me thinking about some of my best VHF SOTA activations, which I will list here.
Sneffels to Pikes
In 2012, for the Colorado 14er Event, Joyce/K0JJW and I climbed Mt Sneffels (W0C/UR-001) at 14,150 feet in elevation. I worked Stu/W0STU on Pikes Peak (W0C/FR-004). We both were running 5 watts on 2m FM, with 3-element Arrow II antennas. I had an FT-817, while Stu used an HT. We made the QSO without too much difficulty, at a distance of 160 miles. Stu put together this video that shows the action on both summits.
Capulin Mountain (W5N/SG-009) is out in the middle of nowhere New Mexico, a long distance from populated areas. My goal was to activate it (and get the points) on VHF, but I knew it would be a challenge. I put the word out to the weak-signal VHF community and used my FT-817 (5 watts) and 3-element Yagi to make contacts. My best DX was with Arne/N7KA at 184 miles. I could hear him fine on SSB but he could not copy me, so we switched to CW to complete the QSO. Arne used a 2M12 Yagi antenna with 700 watts of power vs my 5 watts.
This turned out to be a good lesson in what happens when the two stations are imbalanced with respect to RF power. My 5 watts vs his 700 watts is a difference of 21 dB. No wonder I could hear him just fine but he was struggling to copy me. Flipping over to CW narrows the receiver bandwidth, improving the signal-to-noise ratio, and was enough improvement to make the QSO.
Mount Scott (W5O/WI-002) is a drive-up summit (elevation 2464 feet) in the Witchita Mountains of Oklahoma. It sticks up high enough to have a good radio horizon in all directions. We stopped there to do an activation in March 2018, using the Yaesu FT-90 (set for 30 to 50 watts) and the 3-element Yagi antenna.
We easily worked a bunch of stations on 146.52 MHz FM, including K5RTN in Brownfield, TX. Later, I checked the distance to Brownfield and found that it was 245 miles, which is still my best SOTA DX on 2m FM. There was probably some favorable propagation that morning, perhaps some ducting, for this to occur. K5RTN was operating from home and I am not sure about his power and antenna.
During the 2021 January VHF Contest, we decided to activate Threemile Mountain (W0C/SP-107), which is usually accessible, even in the winter months. Because it is in the Pike National Forest (K-4404), I did a combo operation of SOTA, POTA, and VHF contest. At 10,020 feet in elevation, it is not the highest summit in the region but it has a good radio horizon in all directions.
Also, the hike is relatively short, so I packed the Yaesu FT-991 and a 20 Ah battery, which gave me more power (50 watts) on 2m and 70 cm. Not only that, I actually fired it up below 50 MHz and made some HF contacts, using single-band end-fed halfwave antennas.
I was working a few stations in Denver on 2m SSB when I heard Larry/N0LL calling me from Smith Center, KS. Larry is a well-known Big Gun on VHF with excellent antennas. I’ve worked him in past contests on various bands and modes but I was surprised how strong he was coming in at Threemile Mountain. We probably had favorable conditions on 2 meters that day but nothing exotic, to make a 372 mile QSO. I’ve worked longer distances on 2 meters but this is my best DX for SOTA.
Power and Antenna
Most ham transceivers have decent receivers, so the choice of radio on the receive side is not that critical. (OK, you can add a preamp in front of the receiver to improve it.) The big difference for making QSOs (or not) on 2 meters is antenna and power level.
Improving your antenna is normally the first step in improving your VHF SOTA station, because it helps on both transmit and receive. Joyce/K0JJW and I almost always use the 3-element handheld Yagi from Arrow Antenna. Arrow does not specify the gain, but various sources have measured it at 6 dBd. We have made many QSOs over the years where the extra 6 dB made the difference. An omnidirectional antenna would have come up short. I’ve been looking for a higher gain antenna to use for SOTA but have not found one that I like. Adam’s 8-element antenna is tempting but longer antennas pretty much require a mast, which adds weight to the pack. One of the benefits of the 3-element Arrow is that it is handheld, so we don’t carry a mast. Of course, having two of us activating together really helps…one person can hold the antenna while the other operates and logs. A handheld antenna with a single operator can be a challenge.
Concerning power level, the Capulin QSO with N7KA illustrates what happens when two stations are imbalanced with respect to RF power. After this experience, I did purchase a small 2m amplifier that boosts the 5 watts from the FT-817 to 35 watts. It is compact and not too much of a DC power hog. I think we also heard an imbalance with the QSO between K6ARK and KE9AJ. KE9AJ’s signal was a bit noisy at K6ARK while K6ARK’s signal was full quieting 59 at the other end. This is not a surprise with K6ARK at around 120 watts and K6ARK at 6 watts (13 dB difference).
For higher power on 2 meters, you generally need to bring a bigger radio or an amplifier. The popular HT is generally limited to about 5 watts. For 2m FM, we’ve been carrying the Yaesu FT-90, which is a pretty compact radio and can put out 50 watts of RF power (FM only). On the Threemile Mountain activation mentioned above, we took the FT-991, which is not very SOTA friendly, but it also does 50 watts on 2 meters…and all modes.
Battery capacity also comes into play as higher power requires more DC current. The FT-90 manual says it draws 9.5 amps at full 50 watts of power on 2 meters. (We usually run it at lower power but will punch it up to 50 watts when required.) The FT-991 manual says it draws 15 amps when transmitting at full power on 2m or 70cm. My 160 watt 2m (Mirage) amplifier can draw up to 30 amps on transmit. Wowzy, that’s some real current! The point is that as you increase power, you need to look at your battery situation more carefully.
It might sound like I am suggesting that we should maintain a power balance between the two stations. That’s not the case and is often not even practical. When one station is much stronger than the other, it can be used to advantage. The stronger station is easily heard and the weaker station can point the antenna in the right direction to peak up the signal. The weaker station consistently hears the stronger station, so now the challenge becomes to just get a few seconds of successful transmission in the opposite direction. You keep trying until the weaker station manages to get through. Compare this to having two lower power stations trying to make a contact. They may not even hear each other at all because the antennas are not pointed optimally. When they do hear each other, they are both struggling to hear the other station and complete the QSO. This lowers the probability of completing the contact.
So how much power should you run on 2 meters for SOTA? Of course, More Is Better, except for the extra weight in your backpack. The difficulty of the hike comes into play…on shorter hikes, weight does not matter so much. I am finding that 5 watts is on the skimpy side. On the other hand, going much above 50 watts requires larger batteries, so I am thinking the sweet spot is around 30 to 50 watts. If I do happen to work a base station running 1kW, my signal will be 13 dB lower with 50 watts (worst-case scenario). This is just my opinion, your mileage may vary.
So can we all agree then that VHF signals can go beyond line-of-sight? These examples are basic tropospheric paths and do not include the exotic propagation modes such as meteor scatter, sporadic-e, aurora, EME, etc. I’ve used most of those modes to work longer distances but not during a SOTA activation. Most hams know that SSB and CW are more effective than FM when signals are weak. In fact, FM weak-signal performance is lousy. Still, we see multiple examples of making some long-distance contacts with FM.
73 Bob K0NR
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