Confused about HD signal strengths

[ai4i]

I was surprised / confused to recently find that some channels within a digital stream are more receivable than others.
I tuned into a local HD3 which was choppy, tuned to the same station's HD2 and it held rock solid.
Of course channels within a digital stream have different bandwidth, frequency response, volume, but they also seem not to be equally receivable. My test station (WEAT-FM) runs stereo music on HD2 and is testing with sportstalk on HD3.

[BroadcastDoc]

It could be that way if the station is using Extended Hybrid mode and placing their HD3 in the extended partition. The extended partition is adjacent to the analog signal, and if the station is regularly overmodulating it will degrade the carriers.

[ai4i]

This is precisely what the CE at the station told me, that the HD3 suffers much more from the main carrier than the HD1 or 2 would.

[BroadcastDoc]

I am now running an HD3 here, but I'm not using Extended Hybrid mode. All of the digital signals are of equal strength - all I'm doing is re-allocating the bits!

[NECRAT]

how do they sound?

[BroadcastDoc]

Good! As long as you process it correctly, you can use a low bit-rate codec pretty successfully. I'm running the AM on HD3 using 16k, and I've rolled off the audio at 8k. That eliminates a lot of artifacts.

I do hear a lot of FM HD done poorly, which does live up to the horror stories. When you do it right, however, it works great.

[skugger]

this thread is probably the best fit for the questions i have, regarding our HD transmitter. i'm a little hesitant to put this out there - my apologies to any unemployed or underemployed engineers out there - but i'm an IT guy whose been hired to do my usual IT duties, as well as to start working my way into the role of broadcast engineer as well. i have a bit of an electronics education, but this is still proving to be a challenge. i have no mentor to speak of.

we have a BE fmi1405 transmitter running in iboc-only mode, and it's broadcasting HD1, HD2, HD3, and HD4. right next to it in the shack is an aging analog transmitter putting out 100kw ERP on the same frequency. we're suffering from frequent and persistent signal dropouts on all four HDs, where signal losses will occur every few minutes & last 5 - 15 seconds each, on average. as you might imagine, we have HD receivers scattered all over the building here, 2.5 miles down the hill from the tower, & they all seem to drop out at different times. it's just as bad in my car, even when driving past the tower.

in my opinion, the dropouts got worse when we added HD4, and it's HD4 that seems to suffer from dropouts the most. we have a Belar HD monitor that i've recently gotten working again, so i have some actual data to look at & work with, i'm just not sure (yet) how to interpret it. when i look at the spectrum, it looks like the analog occasionally swells loud enough to overpower the HD sidebands.

i don't want to be an example of HD horror stories anymore if anyone has any thoughts, knows of a decent troubleshooting resource, or has other advice, i'm all ears!

[ai4i]

Why or when would one use the Extended Hybrid mode?
Does it put more power into the HD 1 & 2 by taking it from the 3 & 4?

[BroadcastDoc]

Skugger-

That may be exactly what's happening. In extended hybrid mode, the digital carriers begin to enter the analog audio carrier space. If your modulation exceeds about 110%, the analog audio encroaches into the digital sidebands...that could certainly result in loss of acquisition if it's extreme enough.

ai4i-

You do further de-rate the transmitter when you go into extended hybrid mode, since you are adding more digital carriers...so if you are at full power on your digital transmitter, and turn on the extra partitions, your average power drops a bit. You would use extended hybrid mode if you want to have a few more bits available for your audio. Hybrid mode gives you 96kbps, while extended gives you 112kbps.

[Sam Buca]

this thread is probably the best fit for the questions i have, regarding our HD transmitter. i'm a little hesitant to put this out there - my apologies to any unemployed or underemployed engineers out there - but i'm an IT guy whose been hired to do my usual IT duties, as well as to start working my way into the role of broadcast engineer as well. i have a bit of an electronics education, but this is still proving to be a challenge. i have no mentor to speak of.

we have a BE fmi1405 transmitter running in iboc-only mode, and it's broadcasting HD1, HD2, HD3, and HD4. right next to it in the shack is an aging analog transmitter putting out 100kw ERP on the same frequency. we're suffering from frequent and persistent signal dropouts on all four HDs, where signal losses will occur every few minutes & last 5 - 15 seconds each, on average. as you might imagine, we have HD receivers scattered all over the building here, 2.5 miles down the hill from the tower, & they all seem to drop out at different times. it's just as bad in my car, even when driving past the tower.

in my opinion, the dropouts got worse when we added HD4, and it's HD4 that seems to suffer from dropouts the most. we have a Belar HD monitor that i've recently gotten working again, so i have some actual data to look at & work with, i'm just not sure (yet) how to interpret it. when i look at the spectrum, it looks like the analog occasionally swells loud enough to overpower the HD sidebands.

i don't want to be an example of HD horror stories anymore if anyone has any thoughts, knows of a decent troubleshooting resource, or has other advice, i'm all ears!

You know what's interesting? I'm having the same problem on completely different hardware using Harris gear. MPS, SPS1 and SPS2....the SPS2 will randomly drop out. I think it may be related to the sync between the importer/exporter. We don't use GPS and I don't sync the AES clock so the SPS2 encoder program will give "dropping audio" notices. We solved part of that problem on the SPS1 by syncing the exporter's clock to the importer's audio card clock input.