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

The post Weak-Signal Performance of Common Modulation Formats appeared first on The KØNR Radio Site.

I caused a minor kerfuffle on Twitter recently, when I posted this:

This connector, properly called a PL-259, is the most common RF connector for ham radio use. The female counterpart is called the SO-239 connector. While these connectors are often “UHF” connectors, they actually don’t perform very well at those frequencies (300 to 3000 MHz). So I feel justified in disparaging that name.

The tweet generated a large number of replies, mostly in support of my anti-UHF-naming sentiment. It seems that other highly-educated and thoughtful radio amateurs agree with me. (It seems that the wise hams out there always agree with me.) You should be able to view the thread here: https://twitter.com/K0NR/status/1653575723838492672

Some people pushed back on the anti-UHF sentiment, usually saying that it is the common name for this connecter. A few folks pointed out that Amphenol calls these things “UHF Connectors”, which did surprise me. Who am I to disagree with this manufacturer of high-quality connectors? Of course, Amphenol also says this:

Originally intended for use as a video connector in radar applications, UHF coaxial connectors are general purpose units developed for use in low frequency systems from 0.6 – 300 MHz. Invented for use in the radio industry in the 1930’s, UHF is an acronym for Ultra High Frequency because at the time 300 MHz was considered high frequency. They can be used when impedance mating is not required.

Well, there you have it: the connector was named UHF back when UHF meant up to 300 MHz. (Today, UHF means 300 to 3000 MHz). I particularly like the comment “They can be used when impedance mating is not required.” What? That does not sound good for RF applications. I do agree that these connectors can generally be used to 300 MHz, but these days the ITU calls that VHF (30 to 300 MHz).

Wikipedia provides a more complete explanation, worth reading.

OK, so the name “UHF” is archaic but it has kind of stuck, the way old terminology sometimes does. I am still going to avoid using this term because it really should be deprecated.

And don’t use these connectors above 300 MHz (UHF frequencies). Unless you have to. Which I did last weekend when the only cable available for my 440 MHz antenna had a PL-259 connector on it.

73 Bob K0NR

The post About That UHF Connector appeared first on The KØNR Radio Site.

I have my opinion on ARRL asking FCC to grant more HF privileges to Technician-class licensees.

I verbalize them in this video:

[embedyt]https://www.youtube.com/watch?v=BWSAvDWE3Js[/embedyt]

After you hear my comments, please leave your comments.

Thanks, 73 de NW7US dit dit

I got a Skype call a few weeks ago from Eric, 4Z1UG–the creator and host of the QSO Today Podcast–during which he asked me about how and why I got into amateur radio.  Here’s the result.

Eric writes,

We talk a lot about the band conditions due to the Sunspot cycle. Most of it on Facebook and other places is about how “dead” the bands are at this point. We all can’t wait until the cycle starts to rise and we will be making contacts with little effort. I remember in my conversation with Chuck Adams, K7QO in Episode 58, that he really enjoys operating is “Pigrig”, one watt, CW transceiver on 20 meters. When I asked him, (I liberally paraphrase) “but Chuck, the bands are dead. How does that work for you?”. His reply was that while most hams are listening to the bands, he calls CQ until he gets a reply. Works every time.

My QSO this week is with Tomas Hood, NW7US, who has years of expertise in propagation and Solar activity. He is the propagation editor of more than a few radio magazines and websites. In our post-recording conversation we discussed this phenomenon of listening and not calling CQ. I even had this idea that maybe one of the reasons that the digital modes are so successful is because they “beacon”, as part of the whole digital experience, the same as calling CQ. This is why they make contacts. From what I see, looking at PSK Reporter, hams are making lots of contacts worldwide using the digital modes. While SSB may not be working so well, CW and the digital modes seem to work fine.

I like to work on my bench or make the podcast while listening to the bands. Jeff Damm, WA7MLH, in Episode 177, says that he will put his keyer in CQ mode while he is working on a new radio. Invariably, sometimes after many minutes, he gets a reply. Great idea Jeff!

73,

Eric, 4Z1UG

Episode 184 can be found here: https://www.qsotoday.com/podcasts/nw7us

Highlights of Episode 184:

Tomas Hood, NW7US is the propagation editor of a number of shortwave and amateur radio magazines, and has a wide variety of websites, that grew out of his love for all things radio, and for listening on the bands to far off DX and commercial broadcast stations. Tomas shares his understanding of propagation and the lessons we can learn from listening, really listening to the QSOs and exchanges during contest operation.

All of the QSO Today episodes are great.  I enjoy hearing about many different hams.  Do check out all of the episodes that Eric has published.

73 de NW7US dit dit

 

What got you interested in radio? What hooked you?

I’ve been asked, “What got you interested in radio, space weather, and the science of radio-wave propagation?”

Here’s a short answer as to why (and when) I became a radio enthusiast. It all started…

[embedyt] https://www.youtube.com/watch?v=0XBth62JgwA[/embedyt]

https://www.youtube.com/watch?v=0XBth62JgwA

The following picture is of my first shortwave radio, discovered in my home sometime between 1971 and 1973: a Sony portable transistorized four-band radio receiver. This was my very first shortwave radio (well, truthfully, it was my dad’s). This radio is responsible for my love of radio, electronics, and communications.

I still use this, sometimes, when listening to late-night AM-broadcast-band-radio DX. It is horrible for shortwave radio listening, as it has no noise blanker. For MW (Medium-wave) AM Broadcast DXing at night, it is excellent. The internal bar antenna is very directional so I can rotate the radio around until I get the best reception of some station. Back when I was a child, that made the radio very fun to use.

This next radio is a really capable military surplus radio circa WWII or shortly after (the late 1940s, early 1950s). This radio was my world starting around 1975. From Medium-wave to Shortwave, this radio could hear a pin drop around the world! Many late nights when I was supposed to be sleeping, I was up with the light dimmed and the tubes singing signals from exotic places.

What is your story?73 de NW7US

Addendum:
https://www.youtube.com/watch?v=y8bBM9Dy38o

[embedyt] https://www.youtube.com/watch?v=y8bBM9Dy38o[/embedyt]

Are you interested in starting out with the amateur-radio digital modes on the high frequencies? Have you heard of FLDigi? FLDigi is a software control and modem suite that interfaces with your transceiver, your computer sound card, and other input/output interfaces so that you can receive and transmit one of many digital modes. For example, FLDigi allows you to operate using the Olivia digital mode.

Unlike the JT/FT digital modes–modes that do an incredible job under marginal propagation conditions–there are other modes that offer keyboard-to-keyboard conversational QSO opportunities that can overcome rough shortwave radio propagation conditions. (The meaning of QSO on Wikipedia: An amateur radio contact, more commonly referred to as simply a “contact”, is an exchange of information between two amateur radio stations.)

While making quick work of getting DX stations into your logbook by exchanging callsigns, a signal report, and a grid square, the JT/FT modes (JT stands for Joe Taylor, the fellow that pioneered these modes) are limited. They cannot handle any additional communications beyond a callsign, a signal report, a grid square, and a very limited set of acknowledgments and sign-off messages.

When you desire to get to know people from other areas of the world, or if you need to establish networks around the world for passing information–perhaps an emergency net in support of the Red Cross–or if you are motivated by any other of a myriad reasons to establish a keyboard-to-keyboard conversation by way of the ionosphere, modes like Olivia are great candidates for your consideration.

In this video, contributing editor with CQ Amateur Radio Magazine, NW7US shares some starting points in the FLDigi software for Olivia keyboard-to-keyboard chat mode.

[embedyt] https://www.youtube.com/watch?v=ejSNfXiT8FE[/embedyt]

Current CENTER Frequencies With 8/250 in MHz:

1.8269, 3.5729, 7.0729, 10.1429, 14.0729, 18.1029, 21.0729, 24.9229, 28.1229, and so on. See the pattern?

By the way: The current suggested CENTER frequency With 16/1000 or 32/1000 on 20 meters is 14.1059.

(Why the …9 frequencies? Experts say that ending in a non-zero, odd number is easier to remember!)

Q: What’s a ‘CENTER’ Frequency? Is That Where I Set My Radio’s Dial?

For those new to waterfalls: the CENTER frequency is the CENTER of the cursor shown by common software. The cursor is what you use to set the transceiver’s frequency on the waterfall. If your software’s waterfall shows the frequency, then you simply place the cursor so that its center is right on the center frequency listed, above. If your software is set to show OFFSET, then you might, for example, set your radio’s dial frequency to 14.0714, and place the center of your waterfall cursor to 1500 (1500 Hz). That would translate to the 14.0729 CENTER frequency.

The FLDigi Manual of Operation is found here: http://www.w1hkj.com/FldigiHelp/

FLDigi can be downloaded here: https://sourceforge.net/projects/fldigi/

Join the Olivia movement:

1. Subscribe to the mailing list: https://Groups.io/g/Olivia

2. Join the Facebook group: https://www.facebook.com/groups/olivia.hf

For additional information on Olivia, check out:

http://blog.nw7us.us/post/168515010062/olivia-digital-mode-great-compromise

http://blog.nw7us.us/post/169114702522/are-you-an-amateur-ham-radio-operator-check-out

73 de NW7US

Some HF digital modes were designed for long-distance (DX) radio-wave propagation via the ionosphere. One such keyboard-to-keyboard digital mode is Olivia.

Friday evening, 8 December 2017, at 0200 UTC {9-DEC}, Larry, N7ZDR, called an Olivia-mode 80-Meter digital roundtable net. The following video is a snapshot of about nine minutes of on-air net operations as received at my location in Omaha, Nebraska.  My antenna is a wire run from an SEA marine autotuner mounted under the three-story-high roof’s eaves.  I live in a high-RF environment within two miles of eight high-powered broadcast antenna facilities–TV, FM, AM–as well as business and public-service transmitters.   All that RF desensitizes my receiver.  The noise floor is also affected by industrial-level man-made RF noise.

No, Olivia is not lightening-fast keyboard-to-keyboard chatting, but it can get the job done. This following video shows some real-world operation in which the very weakest signals did not decode well. However, even with the 80-Meter band (center frequency is 3585 kHz) really difficult to work with, it did well in terms of what was available for the Ham Radio Deluxe DM780 software to decode.

Example QSO in Olivia Video:

[embedyt]https://www.youtube.com/watch?v=G7TlGEuStx4[/embedyt]

In 2005, SP9VRC, Pawel Jalocha, released to the world a mode that he developed starting in 2003 to overcome difficult radio signal propagation conditions on the shortwave (high-frequency, or HF) bands. By difficult, we are talking significant phase distortions and low signal-to-noise ratios (SNR) plus multipath propagation effects. The Olivia-modulated radio signals are decoded even when it is ten to fourteen dB below the noise floor. That means that Olivia is decoded when the amplitude of the noise is slightly over three times that of the digital signal!

Olivia decodes well under other conditions that are a complex mix of atmospheric noise, signal fading (QSB), interference (QRM), polar flutter caused by a radio signal traversing a polar path. Olivia is even capable when the signal is affected by auroral conditions (including the Sporadic-E Auroral Mode, where signals are refracted off of the highly-energized E-region in which the Aurora is active).

Currently, the only other digital modes that match or exceed Olivia in their sensitivity are some of the modes designed by Joe Taylor as implemented in the WSJT programs, including FT8, JT65A, and JT65-HF–each of which are certainly limited in usage and definitely not able to provide true conversation capabilities.  Olivia is useful for emergency communications, unlike JT65A or the newly popular FT8. One other mode is better than Olivia for keyboard-to-keyboard comms under difficult conditions: MT63. Yet, Olivia is a good compromise that delivers a lot.

Join us — not just on the HF waterfall, but by joining our email-based group at:

–> https://Groups.Io/g/olivia

or, on Facebook at:

–> https://www.facebook.com/groups/olivia.hf

Thanks for spreading the Olivia love!  See you on the waterfall.

Addendum: 

Current CENTER Frequencies With 8/250 (eight tones, 250-Hz bandwidth): 

1.8269 MHz
3.5729 MHz
7.0729 MHz
10.1429 MHz
14.0729 MHz
18.1029 MHz
21.0729 MHz
24.9229 MHz
28.1229 MHz

See the pattern?

The current suggested CENTER frequency with 16/1000 or 32/1000 on 20 meters is 14.1059.

(Why the xxx…9 frequencies? Experts say that ending in a non-zero odd number is easier to remember!)

Q: What’s a ‘CENTER’ Frequency? Is That Where I Set My Radio’s Dial?

For those new to waterfalls: the CENTER frequency is the CENTER of the cursor shown by common software. The cursor is what you use to set the transceiver’s frequency on the waterfall. If your software’s waterfall shows the frequency, then you simply place the cursor so that its center is right on the center frequency listed, above. If your software is set to show OFFSET, then you might, for example, set your radio’s dial frequency to 14.0714, and place the center of your waterfall cursor to 1500 (1500 Hz). That would translate to the 14.0729 CENTER frequency.

The standard Olivia formats (shown as the number of tones/bandwidth in Hz) are 8/250, 8/500, 16/500, 8/1000, 16/1000, and 32/1000. Some even use 16/2000 for series emergency communication. The most commonly-used formats are 16/500, 8/500, and 8/250. However, the 32/1000 and 16/1000 configurations are popular in some areas of the world (Europe) and on certain bands.

These different choices in bandwidth and tone settings can cause some confusion and problems–so many formats and so many other digital modes can make it difficult to figure out which mode you are seeing and hearing. After getting used to the sound and look of Olivia in the waterfall, though, it becomes easier to identify the format when you encounter it. To aid in your detection of what mode is being used, there is a feature of many digital-mode software implementation suites: the RSID. The next video, below, is a demonstration on how to set the Reed-Solomon Identification (RSID) feature in Ham Radio Deluxe’s Digital Master 780 module (HRD DM780).

I encourage ALL operators, using any digital mode such as Olivia, to TURN ON the RSID feature as shown in this example. In Fldigi, the RSID is the TXID and RXID; make sure to Check (turn on) each, the TXID and RXID.

Please, make sure you are using the RSID (Reed Solomon Identification – RSID or TXID, RXID) option in your software. RSID transmits a short burst at the start of your transmission which identifies the mode you are using. When it does that, those amateur radio operators also using RSID while listening will be alerted by their software that you are transmitting in the specific mode (Olivia, hopefully), the settings (like 8/250), and where on the waterfall your transmission is located. This might be a popup window and/or text on the receive text panel. When the operator clicks on that, the software moves the waterfall cursor right on top of the signal and changes the mode in the software. This will help you make more contacts!

RSID Setting:

[embedyt]https://www.youtube.com/watch?v=lBIacwD9nNM[/embedyt]

+ NOTE 1: The MixW software doesn’t have RSID features. Request it!

+ NOTE 2: A problem exists in the current paid version of HRD’s DM780: the DM780 RSID popup box that lists the frequency, mode, and configuration with a link to click, does not work. HRD support is aware of the problem. You can still use the textual version that shows up in the DECODED TEXT window, a feature of RSID that you can select in the HRD DM780 program settings. This setting ensures that the detected RSID details appear in the receive text area. If you click the RSID link that comes across the text area, DM780 will tune to the reported signal, and change to the correct settings.

Voluntary Olivia Channelization 

Since Olivia signals can be decoded even when received signals are extremely weak, (signal to noise ratio of -14db), signals strong enough to be decoded are sometimes below the noise floor and therefore impossible to search for manually. As a result, amateur radio operators have voluntarily decided upon channelization for this mode. This channelization allows even imperceptibly weak signals to be properly tuned for reception and decoding. By common convention amateur stations initiate contacts utilizing 8/250, 16/500, or 32/1000 configuration of the Olivia mode. After negotiating the initial exchange, sometimes one of the operators will suggest switching to other configurations to continue the conversation at more reliable settings, or faster when conditions allow. The following table lists the common center frequencies used in the amateur radio bands.

Olivia (CENTER) Frequencies (kHz) for Calling, Initiating QSOs

It is often best to get on standard calling frequencies with this mode because you can miss a lot of weak signals if you don’t. However, with Olivia activity on the rise AND all the other modes vying for space, a good deal of the time you can operate wherever you can find a clear spot–as close as you can to a standard calling frequency.

Note: some websites publish frequencies in this band, that are right on top of weak-signal JT65, JT9, and FT8 segments. DO NOT QRM weak-signal QSOs!

We (active Olivia community members) suggest 8/250 as the starting settings when calling CQ on the USB frequencies designated as ‘Calling Frequencies.’ A Calling Frequency is a center frequency on which you initially call, ‘CQ CQ CQ. . .’ and then, with the agreement of the answering operator, move to a new nearby frequency, changing the number of tones and bandwidth at your discretion. Even though 8/250 is slow, the CQ call is short. But, it is narrow, to allow room for other QSOs nearby. It is also one of the best possible Olivia configurations for weak-signal decoding.

– End of Addendum –

73