There's no heterodyne (squeal) on SSB when multiple people talk because there's not multiple carriers mixing. SSB is also usually preferred over AM because it concentrates all your power into the single sideband carrying your voice, where AM splits it up into the carrier and two sidebands. So SSB can be heard farther, and uses less bandwidth allowing more signals to be packed into the same space.

I’m a structural engineer, we were taught it this way: AM = Almost Magic FM = F’n Magic There, see how easy that was! 😂 Great video Callum! 73 my friend!

Just to put a name to it, what we're talking about on FM is called the "capture effect." It's not so much a function of the waveform in the RF realm as it is the way the FM decoder works in your radio. All FM receivers, by necessity, contain an RF limiter to prevent overmodulation. This limiter attenuates everything but the strongest signal at the antenna. So, when you're traveling down the highway, listening to the radio, and you hear two stations fluttering back and forth on the same frequency because you're on the fringes of both signals, that's the FM capture effect rapidly switching back and forth between whichever is the strongest at that moment in time. By contrast, AM (and, by extension, SSB) does not exhibit the capture effect, because in AM, the strength of the signal is what being modulated to produce audio, so you get the additive effect instead.

Callum, I’m still new with AM/SSB with ham radio, but I’ve been licensed to fly for the past 18 years, working professionally for the past 8 years. Aircraft radios most definitely don’t allow two pilots to be heard at the same time. On a busy frequency, it’s very common to hear loud squeals when two key up at the same time, and usually either transmission can’t be deciphered (happened a few times today). Sometimes, if one is much closer than the other, but usually not. It’s common for another person also on frequency to call out “Blocked!” any time there’s a “pileup” on an aviation frequency, sometimes causing another squeal when multiple pilots call it out. I still appreciate AM over FM because I’d rather not get the message but know one was trying to be sent rather than have a closer aircraft transmit over ATC and I miss their message entirely due to capture effect.

Thanks Callum. Isabella smashed up that pile up!😊💪

Good explanation Cal. SSB is "kind of" AM, or half AM without a carrier. That's why we hear everything and are able to pick YL's easy. 🙂 Same with AM, when everyone have the same carrier frequency.

On the install of your Genius 8X2 do try to ground the chassis , you can tap an earth electrode into the ground & connect it with a simple earth cable .

FM has a thing called the 'capture effect' which as Cal explains well, means a receiver will only demodulate (i.e. convert to audio) the strongest signal. AM doesn't, so two transmissions can be heard at once. If, however two AM transmitters are going at the same time but are not quite on the same frequency, the carriers will 'beat' with each other causing a 'heterodyne' - which is a squeal or whistle the audio frequency of which is actually the difference in frequency between the two transmissions. At night, on the AM band, sometimes American AM stations' signals make it across the Atlantic. But they're on multiples of 10kHz, whereas European AM stations are on multiples of 9kHz. So if you listen to, say, 909kHz in the UK you'll hear Radio 5 Live. However, if a US AM station on 910kHz is making its way across, you'll hear a 1kHz whistle under the probably stronger Radio 5 Live. AM like this is properly called Double-Sideband Full Carrier. Other versions exist, such as DSB reduced or suppressed carrier, and of course good old single sideband which doesn't transmit the carrier at all, so it's more efficient at the transmitter and doesn't cause heterodynes if more than one signal is received at once. However its audio quality isn't as good as DSB AM, which is why most international HF broadcast stations still use DSB full-carrier AM. But perfectly good enough quality for voice. I did some experiments a few years ago transmitting music on SSB - I used to have an experimental licence that allowed me to do this. Here's a vid of music being transmitted on SSB - it's possible to make it sound pretty good, but the quality depends on really well set up transmitters and properly tuned receivers. kzfaq.info/get/bejne/ZrmCiMelyJ-zhnk.html By the way, I'm not for one second disagreeing or countering Cal's excellent explanation, just expanding upon it a bit for those interested. If you're not interested, don't read this!

When you mix two frequencies you get three products. Like when you mix 3KHz with 27MHz, you get 27MHz minus 3KHz you get the 27MHz and you get 27Mhz plus 3Khz. This is what a normal AM signal looks like. The minus is the lower sideband, the middle is in this example the carrier and the plus is the upper side band. So when you talk in your microphone you get the carries plus two sidebands. Now the carrier does not have any information. The information is in the two sidebands. And since the two sidebands contain the same information, you only need to transmit one sideband, the lower our the uppere sideband. So what you do with a balanced modulator is surpress the carrier, since the carrier does not contain information. So you left with only two sidebands. Now what you need to do is surpress one sideband. This is done with a crystal filter. You either surpress the lower sideband our you surpress the upper side band. Leaving you with one sideband to transimt and you can put all your HF power in the one sideband. This is single sideband. The carrier is only needed to demodulate the signal and can be provided in your receiver and this is done with a circuit called BFO (Beat Frequency Osaclillator) and should be placed at the exact spot as you should expect the carrier to be. This is why you have your clarifier on your cb-rig. to put the BFO at the exact spot as it should be. Now to make this story more interesting, there is a reason why radio-amateurs use LSB on the bands lower then 10MHz, and USB on the bands higher then 10MHz. Now to use an example we build a radio with a MF (middle frequency) of 9MHz. We mix this with a mixing frequency if 5MHz. This will give us 5+9=14MHz and this will give us 9-5 is 4MHz. If we make this 5MHz variable from 5-5.5 Mhz this will guve is 9+5-5.5= 14 to 14.5 MHz the 20m band. And it will give us 9-5 to 5.5MHz = 4 to 3.5MHz this is the 80m band Now if we mix our LF our voice with the 5MHz signal you will see that if will produce the lower side band on 80m, and the upper side band on 20m. And if we choose to surpress the 14MHz our the 4 MHz you will see that with a few components we can easy build a dual bander. Only the sideband will change because of up, our down mixing. Now you know why we use Lower sideband our Upper side band on some bands. The professionals do not do this.

Hi Callum, thanks for a valiant attempt to explain this very interesting subject! Just to mention what I think was a slip of the tongue: The conventional frequency-deviation, on (narrow) FM communications is about 2.5 kHz I think; 12.5 kHz is the channel-spacing. (This is because the RF bandwidth, of FM, can be much greater than the deviation of the carrier). I wish I could find an on-line version of the great book, about modulation formats, which my dad gave me as I started my Degree in Communication Engineering! Hopefully, those, who would like a better explanation, can find a suitable professional publication on-line; maybe the Institute of Engineering and Technology, in the UK, have something to offer non-members. 73 all!

Just a few days ago I had a visual of how SSB works. I knew how it workded, but I tuned into one of the time broadcasts from WWV. I was set to USB and in the waterfall I could see the signal to one side, I switched to LSB and it moved to the other side of my frequency marker, then switched to AM and watched the same signal take up twice the space in the waterfall on both sided of my frequency marker. It added a visual to what already knew was happening.

Here's a good one.. what is the difference between a "linear" & an "amplifier"?.. linear means straight line & in a linear if you put 2w in & get 20w out if you put 1w in you will get 10w out & this is needed for all the modulation modes where the magnitude/shape of the envelope is important.. that is AM & SSB. This is clean but not very efficient. If your amplifier goes non-linear you will start transmitting spurii & harmonics & you cannot get rid of them so am & SSB amps MUST be "linears". On FM what really matters is the number of zero crossings & the amplitude shape doesn't really matter. You can put FM through a totally non-linear amplifier (that is more efficient) then slug it through a big filter to get rid of all the sproggies & you are still ok. Based on this if you have a 2m FM amp it won't be a linear so don't put SSB through it.... & If you have a 2m linear that is obviously good for ssb & although FM could go through it it probably isn't spec'ed for a 100% duty cycle mode like FM (or am or some data modes) so you would only be able to run it at a fraction of its max rating to stop it melting down. Be wary not all amplifiers are linears (& if you are trying to boost a hotspot watch what type of amp eBay sends you & what data mode needs what.. it isn't always obvious).😮

I haven't seen FT8 mentioned in this thread. Love it or hate it, it makes full use of the benefits of SSB that are being discussed here. In particular, on one dial frequency, in one 15-second period theoretically there could be a 'pile up' of >50 simultaneous transmissions, each being individually identified and decoded at -20dB thanks to the magic of SSB (and some cool software).

Thank you for sharing as always . I wanted to mention that I've recently been researching the huge benefits of coax cable through copper tubing , amazing noise reduction & very low RF loss , the copper tubing has to be grounded to prevent electrolysis , but coax in copper tubing under ground will be ideal within your location .

I do AM on 75m an 40m, every once in awhile I will be on 10m calling CQ around 29.050. It's a fun mode when conditions are good.

You could do a test on the air- switch between ssb am and fm on a 10m qso with a station and see how it changes.

Nice simple explanation Callum, makes perfect sense. I wonder why UK CB went FM in that case?

Imagine my surprise this morning, when I was having my coffee, that I hear you call out my "handle"! Now, I understand the difference between Amplitude Modulation (AM) and Frequency Modulation (FM), and that sideband is just that: either the upper or lower "side" or half of the wave. Now that just made me wonder: Can you "sideband" on both AM and FM? My experience is with CB (so far), which until recently, has been strictly AM. What I"m still not understanding is why the "squeal" occurs when two operators key-up at the same time. I understand that proximity is a factor, but Is it the squeal caused by the two transmitted frequencies being in-sync or out-of-sync with each other? Here's a musical analogy: I play a 12-string guitar, and when I'm tuning a pair of strings to the same note, they will clash at various rates until they are perfectly in-sync. So then, is the radio squeal (heard by someone beside the two transmitting parties) created by two nearby transmitters that are just a bit out of sync? Thanks for answering my question in a video Cal! 73!

I’m guessing this is why they have the concept of ‘channels’ on FM radios so that 2 signals don’t collide as it were ?

"They've got very high quality pieces of kit, everybody's locked on the right frequency because it's all calibrated right" Not the radio in my aeroplane! :-) Admittedly these days I use a handheld for the 8.33kHz spacing which is a lot better than my old radio in the aeroplane.

FM receivers also don't pick up or respond to atmospheric static or electrical interference, such as lightning, that AM and single sideband receivers pick up. To produce a transmitted modulated AM signal with two sidebands, only one sideband is required to modulate the carrier. I have a couple of old vacuum tube single sideband radios that have a manual carrier control knob on the front panel. In AM, only the upper sideband is produced to modulate the carrier, but you can hear the lower sideband that is also produced when the carrier is modulated by only one sideband. The carrier has to be powerful enough to handle the modulation being produced by the one sideband though. With those old radios, when I reduce the carrier below a certain power level, only the upper sideband is transmitted.As I introduce more carrier power, both upper and lower sidebands are transmitted with the modulated carrier.

Technically (at @2:00 and around). Both AM and FM are "de facto" modulated carriers. The difference is the way of modulation. FM modulates the FREQUENCY of the carrier, AM modulates the AMPLITUDE of the carrier. The real reason why many AM (and SSB with suppressed carrier) stations can be heard at the same time without an issue, is rather simple: If there is no carrier (or there are many carriers on the very same frequency), you can DEMODULATE all (added) AM modulated sinusoidal waveforms without a problem. The key is the ability of demodulation. When general AM or not-suppressed carrier SSB sinusoidal waves are added in a crowd, the problem is: that you'll not be able to demodulate it correctly, because the carrier of the off-frequency transmission will corrupt the "good"/useful part of the other transmission. On FM, the situation is even more complicated. FM "silence" is a clean single-frequency carrier with a pure sinus waveform. The receiver will _always_ lock to the signal with the bigger amplitude (the stronger one) and will try to demodulate the speech (or data, or whatever) relative to the stronger signal's carrier frequency. If there is any, the stronger signal will win and the receiver will clearly demodulate the information, even when the other signal is slightly off-frequency and may corrupt one side of the FM modulation. This is called the FM Capture effect. That's why FM has way better sound quality and is used on commercial radio broadcasts. BTW, there is a very good video explanation of it somewhere here from Tall Paul.

Do you have any videos about elevated verticals? I have went back through and watched a bunch of your videos trying to.find info but can't seem to find any. Thanks

AFAIK, AM is not allowed on 60 meters in the US... There's an AM net on Saturday mornings on 80 meters near me, though... The Midwest Classic Radio net. I've listened in a couple times, but never checked in.

an ice storm just kinked my old cushcraft 40-10 meter vertical so I have a dx commander all band (40 up) on order to come to me friday. opportunity to make an improvement.

One of these days i want to pit a 12 watt SSB cb against a 50 watt GMRS FM radio. Should make an interesting video.

Let's go back in time to the late 1950s. Amateur radio was just seeing the then-new SSB mode. Although AM was still widely used it became relegated to rag-chewing because SSB was proving itself superior for DX. VHF hams were still using AM by a wide margin. FM wouldn't become popular until the early 1970s, when repeater operation became legal, and a flood of abandoned commercial radios hit the markets. Speaking of commercial radio... While the AM vs. FM debate was largely settled, there was still a few users of AM in the 25-30 MHz region. FM was winning because of its ease of use and its simplicity. Truck drivers turned the radio on, set the squelch, and didn't have to fiddle with it again. When skip became an issue CTCSS systems were implemented to deal with the problem.

This is probably a silly question, but could a signal both use AM and FM simultaneously?

And here I was thinking it was the spelling.......

So what s this Lora stuff? Digital mayhem?

AM is ancient modulation!