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Military Monitoring Forum - Discussions regarding monitoring military communications on the ground, in air and at sea. Please keep USCG discussion to this forum also.

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Old 04-22-2017, 9:43 AM
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Default What is the primary transmission protocol for the UHF military aircraft band ?

For voice communication, is it standard AM (double sideband), as is used in the VHF civilian aircraft band ?

If not, what do they use ? Do they use any other protocols for voice communication on that band ?

Does anyone know of a radio service where SSB with a Pilot Carrier is commonly used ?
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Old 04-22-2017, 6:54 PM
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Standard AM for voice transmissions
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Old 04-23-2017, 12:49 AM
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There is a satellite sub-band within this range that uses FM. Most of it is encrypted, I believe, but occasionally you will hear some clear voice, as well.
Satellite reception is best accomplished with an antenna specifically designed for it.

John
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Old 04-23-2017, 4:47 AM
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Default Re: What is the primary transmission protocol for the UHF military aircraft band ?

Thank you.

Does anyone have any idea why - when hams and commercial radio manufacturers switched from AM Double Sideband to AM Single Sideband - they did not include a pilot carrier ?

When I had an HF rig, when I listened to other hams using SSB, I sometimes tuned their signal so their voices sounded higher or lower in pitch than they did in person. I did that because it was sometimes easier to understand them. And since some of my older receivers did not have selectable upper or lower sideband, just a Beat Frequency Oscillator, they were harder to tune.

I've never seen an SSB transmitter that transmitted a pilot carrier. Is transmitting an SSB signal without a pilot carrier technically superior than transmitting a signal with a pilot carrier ?

If so, how ?
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Old 04-23-2017, 9:06 AM
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Quote:
Originally Posted by pandora36 View Post
Does anyone know of a radio service where SSB with a Pilot Carrier is commonly used ?
ACSSB (amplitude companded single sideband) uses SSB with a pilot tone but it never really caught on in the US. I don't know about other parts of the world. There were a few non-military ACSSB conventional systems on VHF high band and trunked systems in the 220-222 MHz band but I don't know if they are still around and I don't think anybody makes the equipment any longer.
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Old 04-23-2017, 9:52 AM
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Default Is SSB with pilot tone superior to SSB without

Good question. SSB without carrier is more power efficient, since the carrier "wastes" a great deal of the overall
power of the signal, but does not convey any voice information. ACSB (which includes one side band with carrier), was up and coming in the early 80's as requiring less bandwidth, and being power efficient. The carrier/pilot tone helps the radio tune the signal without having to fiddle with a fine tuning knob, since being off frequency slightly in SSB changes the pitch of the audio.

My recent reading on the related topic of why AM radio was used (for radio station broadcasting) was cost. Double side band SSB with carrier, which is regular am, was used, even thought it was not terribly efficient, because at the time, it made
for more affordable receivers.

With regard to military aircraft there is another reason to favor AM. Again, from my readings the doppler effect
can be significan if aircraft are closing each other at speed. On an FM signal, since it is frequency modulated
changes in frequency would make undesirable noise on the signal.

There were (and perhaps a few linger)/are a few 220 mhz commercial ACSB systems out there. I recall reading about a wide area system somewhere
up the east coast. A small utility near me lists a 220mhz trunked system on the FCC listings, but I believe they are filing to go with a more modern digital mode. My reading indicates that there were cost/performance issues with these systems. The allowed power levels were not very high. The channels, I believe used on these systems were close together in frequency. This required using more costly and "lossy" filtering systems, which further sucks up the already limited power. Net results was a system that was challenging to provide good coverage with. For example when you have a repeater its nicer to have the user transmit 5mhz or more away from the repeater output, then say .25 mhz away. The former is easier to filter then the latter.

Last edited by kb5udf; 04-23-2017 at 10:04 AM..
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Old 04-23-2017, 10:10 AM
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Quote:
Originally Posted by kb5udf View Post
. The channels, I believe used on these systems were close together in frequency.
That is correct. The 220-222 MHz band has 5 kHz channel spacing but I don't think the trunked systems were assigned adjacent channels in the same system.
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Old 04-23-2017, 10:17 AM
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Quote:
Originally Posted by pandora36 View Post
Thank you.

Does anyone have any idea why - when hams and commercial radio manufacturers switched from AM Double Sideband to AM Single Sideband - they did not include a pilot carrier ?

When I had an HF rig, when I listened to other hams using SSB, I sometimes tuned their signal so their voices sounded higher or lower in pitch than they did in person. I did that because it was sometimes easier to understand them. And since some of my older receivers did not have selectable upper or lower sideband, just a Beat Frequency Oscillator, they were harder to tune.

I've never seen an SSB transmitter that transmitted a pilot carrier. Is transmitting an SSB signal without a pilot carrier technically superior than transmitting a signal with a pilot carrier ?

If so, how ?
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According to the Wikipedia article on ACSSB, it is superior to SSB, and backward compatible with standard SSB radios.
See https://en.wikipedia.org/wiki/Amplit...and_modulation .

Aircraft radios use AM instead of FM because of FM's "Capture Effect."
See https://en.wikipedia.org/wiki/Capture_effect .

But that doesn't affect AM DSB, SSB, or SSB w/pilot carrier.

They may not have changed to SSB on VHF/UHF aircraft and land mobile freqs because of the large installed base.
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Old 04-23-2017, 1:35 PM
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The Canadian Time signal uses USB with a carrier so that it can be received in either AM or USB (but not in LSB), HF Aviation frequencies add a carrier when transmitting SELCAL (Selective Calling) to ensure that the tones are received correctly. There was a lot of SSB with carrier during the changeover of Aviation HF from AM to SSB but once everyone had SSB capability most, if not all, stations dropped the carrier.
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