I live about 30 miles from most of the FM sticks in my area. I have not had any trouble receiving the HD stations on my car radio, but indoor reception is another matter. However, 2 stations recently raised their digital power to -14 dbm, which has helped with building penetration at the edge of the stations analog service area. Another poster mentioned that mobile reception varies by several decades and a power increase wouldn't make much of a difference, but I never had issues with mobile reception - only indoor reception. The same poster said there would be problems near airports, but I never encountered those problems.
-
Get involved.
We want your input!
Apply for Membership and join the conversations about everything related to broadcasting.
After we receive your registration, a moderator will review it. After your registration is approved, you will be permitted to post.
If you use a disposable or false email address, your registration will be rejected.
After your membership is approved, please take a minute to tell us a little bit about yourself.
https://www.radiodiscussions.com/forums/introduce-yourself.1088/
Thanks in advance and have fun!
RadioDiscussions Administrators
Increasing to -14 dbm seems to help reception problems.
- Thread starter Geographer
- Start date
Dry Ridge Kentucky. About 30 miles south of Cincinnati.
You don't have problems down in the valleys where there's not a clear line of sight to the transmitters? That's pretty impressive for being so far out.
Granted, I don't know the Cincy market well, so maybe the terrain is different than I remember.
I'll admit I'm confused by the power levels expressed in terms of HD radio. Early on it seemed everyone used percentages, as in "1% of analog power" at the start, now everyone uses dBm which unfortunately is over my head. Can you or someone tell me in terms of dBm what the 1% equivalent would be (-20?) versus the maximum allowed by the FCC now (-10)?
Granted, I don't know the Cincy market well, so maybe the terrain is different than I remember.
I'll admit I'm confused by the power levels expressed in terms of HD radio. Early on it seemed everyone used percentages, as in "1% of analog power" at the start, now everyone uses dBm which unfortunately is over my head. Can you or someone tell me in terms of dBm what the 1% equivalent would be (-20?) versus the maximum allowed by the FCC now (-10)?
1% = -20 dBm. 10% = -10 dBm. The highest current maximum represents a tenfold increase in digital power. Sounds like a big deal until you consider the realities of FM reception. As you drive around and among manmade and natural obstructions and terrain it's not uncommon to encounter 50 or 60 dB variations in signal strength, which any well-designed and built receiver handles without any fuss whatever. You hear minimal effects - maybe a little picket-fencing or noise pops, but nothing objectionable. (Objective and level-headed) experts have looked at the vaunted tenfold increase and have estimated in office buildings the maximum injection level now allowed, will afford possibly 15 feet better penetration measured from exterior walls.
And in a big percentage of cases, the maximum possible is indeed a 6 dB increase to -14 dBm. So: does the power increase help? Sure. Does it elevate HD to the status of a robust, dependable broadcast service? Hardly. It's yet another band-aid on a system with incurable problems, offered more for PR value than for actual accomplishment.
And in a big percentage of cases, the maximum possible is indeed a 6 dB increase to -14 dBm. So: does the power increase help? Sure. Does it elevate HD to the status of a robust, dependable broadcast service? Hardly. It's yet another band-aid on a system with incurable problems, offered more for PR value than for actual accomplishment.
Savage said:
To clarify this a bit further, the digital power is split between upper and lower adjacent channels -- so at 1% injection, each digital sideband has 23 dB less power than the FM analog carrier, and at 10%, the ratio per sideband is -13 dB.
In other words, a Class B or C2 station operating "10% digital" would be allowed an ERP of 2.5 kW in each of the adjacent channels, based on a standard 50 kW/150 m facility. (In comparison, a full Class A analog station at the same HAAT would be licensed 2.75 kW)
I'm still not sure how 10% (or even 4%) hybrid digital complies with the ITU definition of occupied bandwidth that requires 99% of the energy to fall within the assigned FM channel of 200 kHz. Our friend Jonathan Hardis ponders the same question in his recent comments to the FCC, but I haven't seen the official response.
Also, I have no idea of the proper "emission designator" for hybrid operation, but I do know that the FCC will return STL and RPU applications that don't enter this information correctly on a Part 74 license form.
"dBm" is technically an incorrect term for this purpose. -14 dBm is another way of saying 0.06 milliwatts. -14 dB is a ratio, in this case referenced against the analog power, and is as explained by Savage.
I can't speak for the big percentage of cases, but for me, FM HD is a robust and dependable system. When I turn on my radio and tune into an HD-2, the system works as intended on my car radio, and the stations broadcasting at 4% analog provide good indoor service. I am at or near the 60 dBm contour of most of the FM stations in the nearest market. If the system works for me, I think I can safely say that it works well inside the 75 dbm contour - where most of the listeners are located. The system isn't defective, its merely underpowered! Bring on asymetrical power.Savage said:
PTBoardOp94 said:
I believe it should be "dBc," or dB referenced to the analog carrier level.
The HDs on the big 100kw class C stations in the Minneapolis/St Paul market seemed to carry quite a distance. I could hear them 30 miles away without it dropping out, 40 miles away with dropouts, and gone after 60 miles. That area is pretty flat and the band is clear, with not many stations on the first adjacents. Compare that to the NYC market in which the HD signals are gone after 35 miles and start dropping out after 15 miles.
6kw with a -14dBc HD signal from Empire would provide a 240HD watt signal. A 6kw with a -20dBc HD signal would provide a 60 watt HD signal. Like Mr. Hair said: The dBc equals the power ratio of the HD to the analog carrier. For HD; it's best to think -20dBc as 1% of (analog) carrier power, -14dBc as 6% of (analog) carrier and -10dBc as 10% of analog.
Decibel measurements can be tricky if you don't understand what dB is referenced to and/or representing.
-
Decibel measurements can be tricky if you don't understand what dB is referenced to and/or representing.
-
R
rbrucecarter5
Guest
Nick said:
I do a LOT better than that when I visit Minneapolis, well over 100 miles - maybe 120. Granted that is a Pioneer Supertuner 3D, but still. Maybe - it has something to do with car antennas. Somebody decided 31 inch whips didn't look "cool" and now we only have cute little nubs or elements hidden in windshields. Which equals LOUSY reception. Too bad that movement in cars coincided roughly with the introduction of HD radio. HD could have really benefitted from those whip antennas.
rbrucecarter5 said:
I recognize there's no substitute for the bigger antenna on the fender but I've seen some good results from stubby antennas if they are coupled with a good amplifier. The one in my car (which has since corroded and quit working) did fantastically well for such a small piece of metal, but even it's foot+ length is much bigger than the shark fins I see a lot of newer cars sporting.
I can only imagine the complexity of pairing something like that with a second antenna in the windshield (a la "Diversity Antenna" in old Nissans) with HD.
And thanks to everyone for the dB discussion; it helps put things in perspective.
- Status