I’ve been whining about the fact that for many years the 2m FM calling frequency, 146.52 MHz, was prohibited for use in VHF contests and Field Day. See The One Frequency You Should Never Use on Field Day. Well, the ARRL removed this restriction in 2015, so that issue has been resolved.

The CQ WW VHF contest also prohibited the use of 146.52 MHz, and up until now stuck with it. During the reconfiguration of this contest into two separate contests:  analog contest (CW/SSB/FM) and digital contest (FT8, FT4, etc.), the 146.52 rule was dropped. The rules now say:

Use of commonly recognized repeater frequencies is prohibited. Recognized FM simplex frequencies such as 146.49, .52, .55, and .58, and local-option simplex channels may be used for contest purposes.

Of course, this change is only relevant to the analog contest, as FM is not allowed in the digital contest.

This is a relatively minor change, not earth-shattering at all, but it cleans up an outdated rule in the CW WW VHF contest. This eliminates the need for me to explain to new VHF contesters that you can’t use the calling frequency.

73 Bob K0NR

The post CQ WW VHF Contest Allows 146.52 MHz appeared first on The KØNR Radio Site.

This weekend is the ARRL Field Day, a great opportunity for individual hams, small groups, and radio clubs to get on the ham bands and have some fun. But what is Field Day all about? The ARRL says this:

Field Day is ham radio’s open house. Every June, more than 31,000 hams throughout North America set up temporary transmitting stations in public places to demonstrate ham radio’s science, skill and service to our communities and our nation. It combines public service, emergency preparedness, community outreach, and technical skills all in a single event. Field Day has been an annual event since 1933, and remains the most popular event in ham radio.

I have always thought that one of the great things about Field Day is that it can be tuned to whatever interests you or your club. It can be a Radio Contest, an Emergency Communications Exercise, a Radio Campout; a Food Fest, a Beer-Drinking Party, a Social Event, a SOTA or POTA activation,  a Public Relations event, an Educational Event, a Mentoring or Training event, or (very likely) some combination of these ideas. Or insert your idea here. In other words, “season to taste” and make it your own.

Always remember the Universal Purpose of Amateur Radio:

The Universal Purpose of Amateur Radio is To Have Fun Messing Around with Radios.

If you’re not having fun, you’re not doing it right.

73 Bob K0NR

The post Field Day: Season to Taste appeared first on The KØNR Radio Site.

See Part 2 of this report.

Ofu Island is not easily accessible, so it was a key decision on whether to include it as part of the trip. The more I read about American Samoa, the more I noticed that many of the best photos were from Ofu Island. It has a huge beach that stretches along the south side of the island, located within the national park. Not only that, Ofu has an attractive SOTA summit with an excellent view. So, yeah, we needed to go there.

Getting There

Flights from Pago Pago to Ofu are scheduled for Tuesday and Thursday mornings on Samoa Airways. We wanted more than two days on Ofu, so we arrived on a Thursday with a return flight on the following Tuesday. These are small planes with strict weight limits on baggage: 5 kg (11 lbs) for one carry-on bag and 15 kg (33 lbs) for one checked bag. The airline weighs everything and everybody going onto the flight. You can pay for extra luggage, but you risk having it left behind for a later flight if your flight happens to be overweight.

We opted to take only the essentials to Ofu, repacking our gear to fit into just a few bags. Only the lightweight SOTA station went with us, along with snorkel gear and minimal clothing. Everything else was stored at the Tradewinds Hotel.

Lodging

There are limited lodging options on Ofu. We chose to stay at the Vaoto Lodge, right next to the airstrip. The rooms at the lodge are very basic but do have air conditioners. There are no restaurants on the island. The lodge offers a shared kitchen for its guests to prepare their own meals, as well as a limited but adequate selection of groceries for purchase. This may not work for everyone, but Joyce was able to come up with some excellent meals for us.

Four people were staying at the lodge when we were there, including us. One person was there to work on a government-sponsored project. The other was a tourist from New Zealand. So there were probably only three tourists on Ofu at that time.

The best information I found concerning Ofu is: The Ultimate Guide to Ofu Island, American Samoa. This was very helpful, but also double-check the details concerning lodging and airline flights, as things do change with time. Based on the advice of the locals, we concluded that Tumu Mountain was our only SOTA option on Ofu. Sunuitao Peak and Piumafua Mountain (on Olosega Island, connected to Ofu by a bridge) are not considered hikeable.

Tumu Mountain (KH8/MI-003)
The trail to the summit is 3 miles one-way, with 1500 feet of elevation gain. This trail used to be a road, starts out wide and narrows as the elevation increases. It is overgrown in spots, and there is a rope assist in one difficult spot. This video provides a good overview of the climb. This trail is not in the national park.

Our host at Vaoto Lodge dropped us off at the trailhead and picked us up afterward. The hike begins in some 18-inch-high brush that includes some plants with stickers. I wore shorts and accumulated quite a few scratches on my legs. If I do this hike again, I would start with long pants or gaiters and switch to shorts at the first trail marker, about one-half mile up the trail. This trail marker indicates a left turn that starts the climb up the side of the mountain. As the map shows, there is a big switchback that keeps the slope of the trail reasonable.

Near the summit, we noted a sign indicating a trail to the left for the viewpoint, but we continued to the summit. The actual summit is covered by dense vegetation, so we stopped where the trail faded out, labeled “Operating Location” on the map, within the activation zone. There is a small radio installation here. To get to the actual summit would require a serious bushwhack through the tropical forest.

We set up the SOTA station using our smaller antenna mast (fishing pole) and fired up the IC-705 on 17m FT8. Conditions were not great, but we both worked four stations on HF plus each other on VHF/UHF. We were running behind schedule for our pickup time, so we did not operate any longer than necessary.

On our descent, we took the side trail over to the viewpoint, which was fantastic. This is the best photo we took in American Samoa. We are accustomed to hiking in the Rocky Mountains, where reaching a high summit always provides a great view. Tropical forests are a lot different…the vegetation may not allow you to see anything of interest on a summit. Finding a good viewpoint can be challenging.

POTA (AS-0001)

We found a nice spot on Ofu Beach (-14.17776, -169.65428), about a one-mile walk from Vaoto Lodge that is a great place to snorkel and operate ham radio. There is a little shelter there that provides some protection from rain. We did seven POTA activations from this location using the smaller SOTA station with 10 watts. These QSOs were mainly on 15m and 17m, using digital transmissions (FT8 via the iPhone app and the IC-705).

We were supposed to leave Ofu on Tuesday morning, but our flight was delayed until the afternoon. We were aware that flights to/from Ofu can be delayed or cancelled, and we planned some flexibility into our schedule to mitigate this risk. We still made it to Pago Pago that day, returning to the Tradewinds Hotel. After our wonderful stay on Ofu, this felt like a welcome return to civilization.

We were delighted to have visited Ofu Island and highly recommend it. However, it did add six days to the trip, so it may not work for travelers with a more limited schedule.

Wrap Up On the Whole Trip

This concludes our KH8 trip report. Joyce and I had a fantastic time in American Samoa and enjoyed the ham radio aspect of the trip. The only stations we worked on VHF/UHF were each other, which was not a big surprise, but still disappointing. Oh, well, I guess that’s why we have access to the HF spectrum.

Some additional travel notes here:
K0NR Guide to American Samoa

73 Bob KH8/K0NR

The post KH8 SOTA/POTA (3) – Ofu Island appeared first on The KØNR Radio Site.

See Part 1 of this report.

We arrived at Pago Pago (pronounced “pango pango”) around 9 pm and were met by the shuttle van from Tradewinds Hotel. We stayed there for three nights, then took our 5-day side trip to Ofu Island, returning to Pago and the Tradewinds for another 6 nights.

The next morning, we rented a small SUV from the Tradewinds Hotel, which worked out great. Our first stop was the National Park of American Samoa Visitor Center, a 30-minute drive from the hotel. We received some good information about hiking trails and potential summits. The visitor center is located outside the park, so we made a point to drive a bit further to actually set foot in the park. We were thinking that if our trip got cut short unexpectedly, we wanted to make sure we checked the box on being in the park.

Olotele Mountain (KH8/TI-004)

The next stop was Olotele Mountain. My research on this summit was not conclusive. To start with, I found that some maps showing its location incorrectly, something we worked out when creating the KH8 Association Reference Manual (ARM). Some websites suggest that the summit could be hiked, but they did not provide any details. By studying a variety of maps and satellite photos, I concluded there was probably a road to the top, to support a developed radio site. This summit is not in the national park.

We headed toward Aasu on Route 2 and turned off at (-14.31473, -170.76616) to follow the road leading south to the summit. The road is not well-marked, but easy to spot once you know it’s there. This road passes through a residential area with plenty of barking dogs (they seem to be everywhere in KH8). At the top is a well-developed radio site.

We planned to set up the HF SOTA station and make some contacts from the summit, but the clouds moved in, producing heavy rain. At this point, we opted for a quick VHF activation, just working each other with handheld radios, checking the box on activating the first KH8 summit, but without points. Again, the thought was to get the first KH8 activation in the log, just in case. We also figured we would come back another day and do a more proper activation, earning the 4 points for this summit. And we did return to this summit after our visit to Ofu. We both worked quite a few stations on 10m and 15m using FT8.

Both times we activated Olotele, crews were working at the radio installation. We just chatted with them about what we were doing, and they were fine with that. One guy asked me what frequency we would be on and I said 21 MHz. He replied, “no problem.” We also saw a tour guide bring a group of tourists to the summit, which surprised us because the view is mostly blocked by high vegetation.

Mount Alava (KH8/TI-003)

The next day, we activated Mount Alava. This is a well-known summit and hiking trail, promoted by the national park. The trailhead is relatively well-marked, starting at Fagosa Pass. The trail to this summit is 3.9 miles one-way, with 1,300 vertical feet of elevation gain, located inside the national park. This trail used to be a road, generally wide but overgrown in spots, narrowing as the elevation increases.

While planning the trip, I noticed that the National Park Service had posted an alert on its website that said the trail to Alava was closed. Later, information was posted stating the trail is open, but the summit is off-limits. During our visit to the visitor center, the NPS staff told me that the main trail from Fagasa Pass is usable, with no problems. The specific thing that is not allowed is ascending the broken-down stairs that go up about 30 feet to an old structure, which provides an excellent view of the area. Often, this structure is referred to as “the summit,” and folks will simply say that “the summit is closed.” Trail conditions do change frequently in the tropical climate, so it is best to inquire locally for the latest information.

We activated Alava from near the bottom of these stairs, inside the activation zone. We saw some local folks climb over the locked gate and go up the stairs to get a better view, but we opted not to do the same. I am sure it provides a better view, but we were mostly after radio contacts.

As shown on the maps above, Alava sits on a long ridgeline that the trail follows, making the activation zone quite broad. We stopped about 500 feet west of the actual summit location indicated by the SOTA ARM. The trail seemed to end at this point, at the bottom of the stairs mentioned above. There should be a path that continues to the east, but I was unable to find it. No worries, we were within the activation zone, so we set up and made radio contacts.

This was a challenging hike due to the muddy conditions and the overgrowth of vegetation on the trail.

POTA (AS-0001)

When we arrived in Pago Pago, I expected to find many suitable locations for POTA activations. It turned out to be not quite that simple. Many of the roads skirt the national park instead of going through it. After studying the map a bit more, we settled on the Pola Island Viewpoint on the northeast side of the island. This is a convenient turnout on Route 6, heading to Vatia, also known as the Lower Sauma Ridge Trailhead.

We did seven activations here as KH8/K0NR and KH8/K0JJW. Most of the activity was on 15m and 17m, using FT8, FT4, and SSB. We tried 20m, but the propagation wasn’t all that great and we would get covered by stateside QRM. Bob/W0BV was usually listening and gave us valuable feedback on band conditions and whether our frequency was clear in the US. This was extremely helpful when operating from a remote location. We worked plenty of stateside stations, VK, ZL, JA, HL, B, South America, and the Caribbean.

W0BV recorded some audio of me working POTA on 15m SSB, quite a bit of fading at the time.

The POTA radio setup had the FT-991 in the back of the SUV, connected to my notebook computer for logging and digital operating. We just stood at the back of the vehicle under the hatch, which provided rain cover during the occasional storm. This was not super convenient, but we managed.

We used the power analyzer shown above to monitor the battery voltage, so we didn’t run down the battery. The end-fed antenna was supported by the SOTAbeams pole and connected to the radio using 50 feet of RG-8X coaxial cable. We kept the antenna as far away from the radio as possible and inserted a common-mode filter in line with the coax. This avoided the EMI issues we experienced in Hawaii, so we were able to use the notebook computer running WSJT-X.

The number of POTA contacts (including Ofu Island, described in Part 3) were:
KH8/K0NR: Phone 39, Data 213, Total= 252
KH8/K0JJW: Phone 18, Data 21, Total= 39

Next stop is Ofu Island.
On to Part 3

The post KH8 SOTA/POTA (2) – Tutuila Island appeared first on The KØNR Radio Site.

For decades, Joyce/K0JJW and I have working towards visiting all 63 of the US national parks. We are nearing the end of the list, with just a few parks left. One of the most challenging places to visit is the National Park of American Samoa, located in the only US territory south of the equator. That would be number 61 for us, with only Crater Lake NP and Lassen Volcanic NP left to visit.

Obviously, if we are going to travel to a distant island, we should consider doing a Slacker DXpedition. American Samoa is a US territory, so FCC radio licenses are valid there. It is also a separate entity for DXCC, with the prefix KH8. KH8 is listed at #87 (out of 340) on the Most Wanted list at Clublog, so it is a bit rare in terms of DXCC. Parks On The Air (POTA) has already been set up for KH8 and the national park there has been activated a number of times. I checked into the Summits On The Air (SOTA) situation and discovered there were summits that qualified for the program, but that a KH8 Association did not exist. The next thing you know, I am the KH8 Association Manager working with the SOTA Management Team to establish the KH8 association.

Travel

We usually try to pack light when traveling. On a typical airplane trip, we can generally get by with each of us having one carry-on bag. But once you add snorkel gear, camera gear, binoculars, hiking boots, radio gear, and a few other items, it becomes necessary to check a bag — or two. Still, we focused on keeping the amount of luggage to a minimum so we could navigate the airports without assistance.

To get to KH8, we connected through Hawaii, to catch the main flight to Pago Pago on Hawaiian Airlines. This flight only goes two or three times a week and is the only option coming from the 48 states. We decided to enjoy four days on the island of Kauai, which turned out to be an excellent idea.

Radio Gear

We normally only use frequencies above 50 MHz for SOTA, but given the lack of VHF activity in KH8, we compromised and took along HF gear. Our Icom IC-705 is a good choice for that as it also has the VHF/UHF bands included. We also packed a pair of handheld radios, which were useful for basic communications on and off the trail.

We had two main radio setups: a backpackable station for SOTA and a higher power station for POTA. Scoping out our likely SOTA summits, we definitely needed a compact station that could be carried up some summits that would involve a challenging hike. For this station, we used the IC-705 (10 watts output) driving an end-fed multiband wire antenna from PackTenna, supported by a carbon fiber fishing pole. The IC-705 does not have a built-in antenna tuner, so a small, manual external tuner did that job. A Bioenno 4.5 Ah battery supplied the power to the radio.

The antenna system travels in a small pouch and consists of the Z-match tuner, RG-174 coaxial cable, and the end-fed wire antenna. The antenna can cover 30m up through 10m, using a tuner, so it was an efficient way to cover the bands we planned to use.

With the remote location and QRP power levels, we concluded that SSB might be a limitation. Our solution was to utilize digital modes (FT8 and FT4) to enhance our weak-signal performance. I sometimes operate CW, but I don’t think I can handle the pileups we expected at KH8. Joyce doesn’t do CW at all. Our plan was to use my Windows laptop, running WSJT-X, for digital processing. I would have taken this computer along on the trip anyway, so it made sense to have it do double duty, even though it’s a bit large to carry up the summit—more on that below.

POTA Station

We could have used the SOTA station for POTA as well, and we did in a few situations. However, we opted to take along a Yaesu FT-991, with 100 watts output, thinking that would help us when running SSB and if band conditions are poor. This is our normal POTA radio, powered by a 20 Ah Bioenno battery that can supply 30 amps continuously, providing a decent margin for the FT-991 (max current spec is 23 amps). However, FAA regulations don’t allow large batteries to be taken on an aircraft. I am used to carrying smaller batteries while flying, so this was all new to me. The short story is that you can carry on two lithium batteries, each limited to 160 watt-hours. (Read the regulations carefully yourself to understand the fine points.) For a 12-volt battery, 160 watt-hours corresponds to 13 amp-hours. So maybe I could carry two 13-amp-hour batteries and get by with that. Well, the Bioenno battery, which is the closest in size (12 amp-hour) has a maximum continuous discharge of 20 amps, which is a little light for the FT-991 keyed down at full power. I was also worried about the battery capacity and how long we would be able to operate. (In retrospect, this approach might have worked and deserves further consideration in the future.)

Another option was to take an AC power supply along, which might have been useful, but AC power was not likely to be available at a typical POTA spot. Ultimately, our solution consisted of a power cable with battery clips that connect to the battery in our rental car. We already had our radio gear set up with powerpole connectors, so crafting a cable with battery clips and powerpoles on it did the job. From experience, I know that it is possible to get excited about making radio contacts and overlook the fact that your car battery is now depleted. To avoid this, I inserted a 12-volt power analyzer inline with the DC cable, allowing us to monitor the battery voltage. I was vigilant in monitoring the voltage and running the car engine regularly.

Rounding out the POTA station were two 25-foot lengths of RG-8X coax and an end-fed long wire antenna from MyAntennas. This antenna was needed to handle the higher power level of the FT-991. For antenna support, we used a SOTABeams 32-foot Travel Mast.

The National Park of American Samoa is POTA AS-0001. This park had already been activated 33 times, primarily by KB2FMH and KH8RRC. There are two other POTA parks in KH8 (both unactivated), but we did not operate from them.

Alerts and Spots

Our operating schedule was fluid, so we used the SOTA and POTA websites to post our activations once we decided to go out,  and to spot ourselves once we were on the air. Some of this could be done from our hotel room using an internet connection but at the operating location, we typically did not have a network connection.

We did have a Garmin Inreach satellite communicator that works anywhere on the planet, so we sent messages via the SOTAmat system. This requires some preplanning to set up access and learn the system but it performed well. The only disadvantage to this method is that Inreach messages can take 5 or 10 minutes to send, depending on when the satellite passes over.

Summits On The Air

Complete KH8 SOTA information can be found here in the Association Reference Manual:
https://www.sotadata.org.uk/en/association/KH8

There are 11 SOTA summits in KH8. Many of these are not accessible due to rugged terrain and dense tropical vegetation. The most accessible summits are listed below. See the SOTA database for more information and specific activation tips. In all cases, assume the trail condition can change and inquire locally for the latest information.

Tutuila Island

Olotele Mountain (KH8/TI-004) – Drive Up Summit.
Olotele Mountain is a developed radio site with multiple towers on it. There is a single-lane paved road to the top, making this a drive-up summit. This is the easiest summit in American Samoa. It is NOT in the national park.

Mount Alava (KH8/TI-003) – 3.9 miles one-way, 1300 vertical feet, in the national park.
This is a well-known summit and hiking trail, promoted by the national park. The trailhead is relatively well-marked, starting at Fagosa Pass. This trail used to be a road, generally wide but overgrown in spots.

Matafao Peak (KH8/TI-001) Steep trail, 1500 vertical, 1.5 miles one way
The highest summit in American Samoa. There are widely varying reports on whether the trail to the summit is hikeable or not. Trailhead is at Fagosa Pass. We did not attempt this summit.

Ofu Island

Tumu Mountain (KH8/MI-003) 3.0 miles one-way to the summit with 1500 feet of elevation gain. This trail used to be a road, generally wide but overgrown in spots, rope assist in one spot.

Let’s Go!

So that was the basic plan. Fly to Hawaii, hang out there for a few days, then continue on to American Samoa. Activate a few summits on Tutuila and then travel to Ofu Island to activate one more. Interspersed would be POTA activations, lots of snorkeling, and sightseeing.

More to follow in Part 2.

73 Bob KH8/K0NR

Side Note: Kauai SOTA

We were not focused on SOTA in Kauai, but I looked up what summits were available and discovered the answer to be quite straightforward. Out of the 11 SOTA summits on the island, only one has been activated: Nounou Mountain (KH6/KU-011). The rest are very difficult to access.

So Joyce and I decided to do the summit. As advertised, the trail turned out to be muddy and had some difficult sections requiring some minor rock scrambling. The weather was hot and humid, making this a good warm-up for KH8. In particular, I discovered that my SOTA station had serious EMI problems. I thought I had worked this out back home, but my notebook PC was producing a high level of noise that was interfering with the receiver, and the RF from the transmitter was disrupting the USB data connection. This messed up the activation of Nounou, but it caused me to work on the problem before arriving in KH8.

The workaround I came up with was to use my iPhone with the SDR-Control Mobile  app, connecting to the IC-705 via Wi-Fi. This eliminated the need for the USB cable, which was acting as an EMI radiator. The iPhone display is relatively small for running FT8, and the app has a few anomalies, but it did the job. On the plus side, the iPhone is a lot less to carry up a summit.

The post KH8 SOTA/POTA (1) – The Plan appeared first on The KØNR Radio Site.

Today, Joyce/K0JJW and I activated Kaufman Ridge (W0C/SP-081). This was my 10th activation of this summit and the 8th for Joyce. Kaufman is an easy summit near our cabin, so it is a favorite when we want to do a Summits On The Air (SOTA) activation. I’ve posted about how to activate this summit in the past, but a few things have changed over the years, so this update seems appropriate. Because of the off-trail hiking, we always seem to take a different route each time, but the specific route is not critical. We have learned a few things to avoid on the hike, which are reflected in this post. The one-way hiking distance is about 1.4 miles with 1000 vertical feet.

Getting There

There is no trail and no trailhead. To reach the recommended parking spot, turn south at the top of Trout Creek Pass and follow Windmill Drive (also marked as County Road 318) southeast to San Isabel National Forest. As you enter the forest, you will be on FS318, which has a gate normally closed from Dec 1 to Apr 30. You can still activate the summit when the gate is closed, but you’ll have to hike in on the road.

Pass through the gate going south on FS318 and take a sharp left (almost a U turn) onto FS308. Later, turn right onto a side road, FS308B, which should be marked. Drive a short distance on FS308B until the road is closed to motor vehicles. These roads are easy 4WD and high clearance 2WD will probably work fine. The FS road continues but is closed to motor vehicles at this point. There is a dispersed campsite here, so you may encounter campers. Park here at 38.85979, -105.93318.

The Hike

The hike up Kaufman starts on the old Jeep road, which is easy to follow. Later, this road ends, and the off-trail hiking begins. In the past, we’ve tried just heading straight for the summit (which works), but it can take you into significant downed timber and difficult rocky areas. It is better to head due south, hook around to the west and approach the summit from the east/southeast as shown on the map. This avoids the large aspen grove directly NE of the summit, with lots of downed timber.

There is a medium-sized rock (maybe 2 by 2 by 3 feet) sitting in the open that is a useful landmark to aim for. This waypoint (The Rock) is particularly useful for orienting yourself on the descent. Keep heading south past The Rock and turn slightly southwest toward a ridge that runs NW/SE from the summit. A good place to intersect this ridge is marked as the waypoint Trail on Ridge. Here you will intersect a game trail that runs along the ridge, which you should follow to the summit. This waypoint is also useful on the descent, to let you know when you need to leave the game trail (which continues on SE for a while).

Once you get onto the ridge, you will have a fantastic view of the Collegiate Peaks to the west. A cairn is at the summit with the typical summit register in a jar.

We had a fantastic time today on the summit. Great spring weather, blue sky with a few clouds. We worked a number of stations on 2m and 70 cm: KF0RIG (On Spinney Mountain, W0C/SP-118), KD0MRC, K8QWR, W0XC, K0MGL, K0LTH, W5PYB (mobile), W0BV, K0PF (mobile), and KD0RRD (mobile).

73 Bob K0NR

Waypoints
End of Old Jeep Trail (38.85545, -105.93519)
The Rock (38.85545, -105.93519)
Trail on Ridge (38.84937, -105.94055)
Summit (38.85050, -105.94280)

The post Activating Kaufman Ridge (W0C/SP-081) appeared first on The KØNR Radio Site.

At first, I was just looking around on the web for some simple Rules of Thumb that compare the weak-signal performance of commonly used analog and digital modulation types. I was mostly focused on FT8 and FT4 but I also wanted to compare SSB and CW. I failed to find a simple comparison of these modes but I did find a number of good articles that compared some but not all of them. This article is my attempt to aggregate the available information into something easy to understand.

Disclaimers

I decided to leverage the work of others and to not try deriving everything from basic principles. I am telling myself that I am perfectly capable of doing the analysis but that I would never find the time to actually complete it. (Yeah, that’s my story, and I’m sticking to it.) Where the articles disagree, I tried to identify which one(s) had the most convincing analysis or rationale and used those values.

My goal is to compare common modulation types primarily in terms of weak-signal performance. This means focusing on how well a signal can be detected with low signal-to-noise ratio (SNR). I have ignored other factors, such as signal fading, frequency drift, multipath distortion, etc. Also ignored are factors such as the information rate provided by the modulation type and the required signal bandwidth. This is focused on having the ability to pass just enough info to make the contact.

Literature Survey

Searching the internet provided me with a number of good articles that have examined this topic, listed below in the References section. My approach is to compare the results of these articles and aggregate them into a concise summary. These minimum SNR values are listed in the table shown below, along with my aggregated conclusions in the righthand column.

Most of these articles presented SNR data in terms of a 2500 Hz bandwidth, with the goal of providing an easy comparison between modulation types. SSB is the widest signal discussed, and it roughly fits into a 2500 Hz bandwidth, which is often the IF bandwidth of the receiver being used. Some authors make this explicit by tagging this SNR as SNR2500.  It is common practice in communications work to normalize the bandwidth to 1 Hz, which indicates the modulation’s bandwidth efficiency. However, we’ll stick with SNR2500.

I started with the article by PA3FWM [Ref 1], which provides a look at many of the modes I was interested in comparing. Unfortunately, this article does not include FT4 and FT8. N6MW [Ref 2] has a good treatment of FT4 and FT8 as well as minimum SNR values for SSB and CW. These lined up well with the PA3FWM values, so that was a good sign. N6MW referenced the foundational article about FT4 and FT8, published in QEX, written by the FT4 and FT8 developers [Ref 3]. The KB9II article [Ref 4] focuses on VHF weak-signal performance and provides minimum SNRs for SSB, RTTY, CW, and PSK31. He introduces the concepts of SNR (average) and SNR (peak). I used the SNR (average) numbers in the table. The KF6HI [Ref 5] article provided another set of SNR values that lined up pretty well. Finally, I came across a presentation by K0LB and KK4SNO [Ref 6] that includes a slide summarizing SNR performance. Because it is slideware, it does not include much about the sources of their numbers, but it seems useful to include them in the table.

The authors have somewhat different approaches to determining their SNR2500 numbers, mostly related to the assumptions used. You may want to read through these papers to gain a better understanding of the fine points. Overall, there is good alignment on results, with a few exceptions.

SSB

The single-sideband SNR2500 values are a mix of 10 dB and 6 dB. Frankly, I think 10 dB is a bit high for “minimum SNR” because I’ve spent quite a bit of time making weak-signal VHF/UHF contacts with the signal right at the noise level. I’ve squeezed out radio contacts with SNR much less than 10 dB. I looked at the rationale supplied in the articles for this value and it is mostly just assumed. So I went with my own experience and chose something smaller, 6 dB, aligning with KB9II and KF6HI. Even this number might be a bit conservative.

RTTY

I found only four values for RTTY, and they vary quite a bit. After studying the articles, I judged KB9II to have the best justification, so I went with -9 dB. I suspect that the actual decode performance may vary depending on the type and quality of the detector.

CW

The SNR2500 numbers for CW varied significantly, over a range of 10 dB. One way to estimate CW performance is to use the bandwidth of the receiver and compare it to 2500 Hz. Using a typical CW filter bandwidth of 200 Hz, SNR2500 = 10 log (200/2500) = -11.0 dB. However, it is well-known that the human ear/brain combination provides additional signal processing. The classic article by W2RS [Ref 7] covers this topic quite well. Using actual on-the-air tests, the article explains that the skill of the operator can introduce a variation of 3 to 6 dB. Another interesting note is that if the operator knows in advance the type of information they are expecting (such as the callsign of the other station), it provides a 3-dB advantage.

We can and probably will debate the SNR2500 value for CW until the cows come home, but I decided to adopt -12 dB in the right-hand column. This is probably conservative for a highly skilled operator.

FT8, FT4

For FT8 and FT4, I used the N6MW values, which come directly from the FT4 and FT8 paper [Ref 3]. I rounded off to the nearest decibel to be consistent with the rest of the column.

JT65

The JT65 values are quite consistent. An article by K1JT [Ref 8] says JT65 SNR is “roughly -28 to -24 dB in 2500 Hz,” so I put -24 dB in the righthand column.

WSPR

WSPR is a popular beacon mode and the king of weak-signal reception. Signal reports are collected worldwide and shared via WSPRnet.org. WSPR performance will vary depending on the specific settings used on the software and we have some variation in the table. The K1JT & W1BW article [Ref 9] says, “The WSPR protocol is effective at signal-to-noise ratios as low as –28 dB in a 2500 Hz bandwidth, some 10 to 15 dB below the threshold of audibility.” So I used -28 dB in the aggregated column.

Conclusions

The rightmost column in the table provides a reasonable comparison of the listed modulation types. I don’t claim that the values are perfect, but they should be helpful in understanding the performance of these modes. These data show that SSB is the least sensitive mode, followed by RTTY and PSK31. As mentioned earlier, the CW number is open to debate but it performs better than RTTY and PSK31. This brings us to FT4 and FT8, which are commonly used WSJT protocols with reasonable throughput. (FT4 and FT8 using 7.5 and 15-second transmit/receive intervals.) JT65 operates at lower SNR, but it is really in a different category, It is designed for Earth-Moon-Earth contacts, using one-minute intervals. WSPR is also unique as a beaconing system and not designed for two-way radio contacts, but it does have the best SNR performance on the list.

When using this data, keep in mind that most of these modes degrade slowly so there may not be a sharp cutoff at an exact signal level. The values are Rules of Thumb, accurate to within a few dB.

Thanks to Jim/K5ND and Bob/WØBV for reviewing this article and providing feedback.

73 Bob K0NR

References

1. Signal/noise ratio of digital amateur modes – Pieter-Tjerk de Boer, PA3FWM

2. FT8 Modulation and Decoding – A Dive into SNR interpretation N6MW

3. The FT4 and FT8 Communication Protocols – Steve Franke, K9AN- Bill Somerville, G4WJS – Joe Taylor, K1JT

4. A Comparison of Common Digital Modes for Weak Signal VHF Communications – John Matz, KB9II

5. Signal to Noise Ratio, definition and application to Radio Communications – KF6HI

6. Digital Modes in Amateur Radio – Larry, K0LB and Scott, KK4SNO

7. The Weak-Signal Capability of the Human Ear – Ray Soifer, W2RS

8. EME with JT65 – Joe Taylor, K1JT

9. WSPRing Around the World – Joe Taylor, K1JT, and Bruce Walker, W1BW

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