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What gives?

Ai4i

Ai4i

I park where a particular FM station has some low signal hiss but it pops right into HD and holds HD, of course the hiss vanishes.
Elsewhere, that same station is absolutely full quieting with the volume cranked up but not the slightest trace of HD.
Seems counter-intuitive (sp?).
 
They might be using separate antennas for analog and HD. That could result in signal dropouts in different locations.
 
ai4i said:
I park where a particular FM station has some low signal hiss but it pops right into HD and holds HD, of course the hiss vanishes.
Elsewhere, that same station is absolutely full quieting with the volume cranked up but not the slightest trace of HD.
Seems counter-intuitive (sp?).
Click to expand...

Is it possible that your parking area is in a location where that station has multipath issues? In other words, your radio is not only picking up the signal, but 'echoes' of the signal as it bounces off of nearby buildings/walls/terrain/etc.? I ask because there are a couple of Chicago stations on which the signals can sound poor due to multipath (depending on where I am); yet those stations sound crystal clear in HD. You go from hearing staticy analog audio to perfect HD and it's quite impressive. Apparently, digitizing the signal does prevent multipath signal reception from degrading the audio that you hear. However, in such a case, your issue isn't a weak analog signal as much as it's too strong of a signal.

This is probably HD radio's best asset, though it's not worth Ibiquity 'selling' it because the HD signal drop outs happen probably 10000 times more often than the analog signal being 'saved' by being digitized.

Also, I am not aware of any stations using different transmitter sites for analog and HD signals - nor do I believe that's even possible, regulatorily.

It certainly happens under the British DAB system - but their digital radio is in a different band than FM.
 
Yep, you can have two separate antennae/transmitters, but I believe that they have to be at the same "site" - not even the same tower, but just the same site. Seems to me to be more energy efficient to have one analog system and then one HD-only transmitter/antenna than waste power into a dummy load, and it would be really easy for those stations to implement the power increase with immediate results. Anybody know of these sites?
 
JohnnyElectron said:
Yep, you can have two separate antennae/transmitters, but I believe that they have to be at the same "site" - not even the same tower, but just the same site. Seems to me to be more energy efficient to have one analog system and then one HD-only transmitter/antenna than waste power into a dummy load, and it would be really easy for those stations to implement the power increase with immediate results. Anybody know of these sites?
Click to expand...

The FCC policy for dual antenna IBOC requires that the antenna be within 3 seconds of Lat/Lon and the digital antenna must be within 70-100 % of the height of the analog antenna.

http://fjallfoss.fcc.gov/edocs_public/attachmatch/DA-04-712A1.pdf

However, in cases where the digital antenna is mounted on a different part of the structure than the analog (for example, on a tower leg or face rather than a pole), the patterns may vary several dB in certain directions, causing coverage disparities.

Also, many of these dual-antenna facilities require the station's only aux antenna to be used for digital, so whenever maintenance work is performed on or near the main antenna, the analog transmitter must be patched into the aux and the digital goes bye-bye.
 
audioguy said:
They might be using separate antennas for analog and HD. That could result in signal dropouts in different locations.
Click to expand...

I believe that is what is being done for some if not all the HD enabled FMs on Chicago's Hancock... one mast is about 150 feet from the other.
 
If you don't co-locate the digital and analog antennas as closely as possible, the potential for self-interference increases dramatically. Since it's impossible for separate antennas to occupy the same space at the same time (or so I was taught in high school) there's always the self-interference problem in IBAC. It's just a matter of degree.

The only comprehensive solution is the interleaved purpose-specific IBAC digital-analog radiator. Big buck$$...but at least, there's one serious HD Radio problem solved. ONE down....946 to go.... :D
 
During DX I sometimes can get a completely different station on HD than analog on the same frequency. Even if both the local and the DX station are running IBOC.
 
Savage said:
If you don't co-locate the digital and analog antennas as closely as possible, the potential for self-interference increases dramatically. Since it's impossible for separate antennas to occupy the same space at the same time (or so I was taught in high school) there's always the self-interference problem in IBAC. It's just a matter of degree.

The only comprehensive solution is the interleaved purpose-specific IBAC digital-analog radiator. Big buck$$...but at least, there's one serious HD Radio problem solved. ONE down....946 to go.... :D
Click to expand...

Jampro makes a couple of interesting antennas for this purpose. One series has dual inputs for analog and HD to feed the same bays, and their interleave spins the circular in the opposite direction from the analog.
 
Nick said:
During DX I sometimes can get a completely different station on HD than analog on the same frequency. Even if both the local and the DX station are running IBOC.
Click to expand...

I received the analog signal from WRBI from Batesville Indiana, but my car radio momentarily locked onto the digital signal from WXEG from Dayton. Both stations are on 103.9.
 
I know of an ERI dual-feed job that one broadcaster on the system shut off their ibuz because it worked so well... Not. The other broadcaster is still running theirs. I can take the whip on my spectrum analyzer and move it around, getting all different analog to digital ratios. On a car radio it's pretty easy to hear some self jamming within the first several miles away from their stick. This thing is the equivalent of a 12 bay and pretty much parked right in town. Nope... Not such a great idea in my opinion indeedeee...
 
The station to which I first refered recently moved to a new stick two, maybe three miles from their old one.
I wonder if just maybe...???
 
OKCRadioGuy said:
I know of an ERI dual-feed job that one broadcaster on the system shut off their ibuz because it worked so well... Not. The other broadcaster is still running theirs. I can take the whip on my spectrum analyzer and move it around, getting all different analog to digital ratios. On a car radio it's pretty easy to hear some self jamming within the first several miles away from their stick. This thing is the equivalent of a 12 bay and pretty much parked right in town. Nope... Not such a great idea in my opinion indeedeee...
Click to expand...
I'm not saying I recemmend them, or any other product that goes to the purpose of getting the sham crap moving electrons through the ether, I'm just saying the hardware is out there if you want to play.
 
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