We are talking about completely different things.
Not really. I'm talking about a serious effort to improve FM reception quality - the topic of this thread. A run-of-the-mill translator system was WAAAAY too noisy because of adjacent-channel HD radio interference on the input (not self-interference, I'm speaking of the HD carriers from 89.3 landing on 89.5). Legally we're required to receive the primary station off-air. So we went looking for another method. The two choices were:
1. Receive and rebroadcast the HD transmission.
2. Try to eliminate the noise on the received analog signal
Option number two provided better quality audio, and that's what we chose to do.
There should be no reason for a properly programmed, installed and set up HD to HD link to have objectionable artifacts. Is the HD equipment from the importer to transmitter of factory design or is it an ad hoc assemblage? Something is incorrectly set. I suggest that you seek professional HD guidance because your HD should easily make this link. 1st adjacent HD digital/ HD digital sideband interference is not an issue. The upper/ lower adjacent sidebands have a net 90 degree differential and have reasonable rejection in the QAM detector. A knowledgeable person should comb and correct your HD. Otherwise you are not getting the performance from your system that you have paid such a goodly sum for!
When the interfering signal is that of another station the upper-lower sideband problem is a big one indeed. That's our issue, and in fact that is the entire reason we secured this translator. It brought back thousands of listeners that were lost with the implementation of HD Radio. While I wasn't part of the original implementation, it was done as a turnkey by Harris with an Omnia and it's all reasonable.
Your definition of "objectionable artifacts" is certainly up to the individual listener. I know I can hear the clanky-swooshy sound of an AAC codec that I first became familiar with on XM - especially when airing cell phone calls. Whether 1%, 5%, or zero listeners would notice if we used the HD signal for the translator rebroadcast, I'm not sure. But why should we retransmit a compromised signal when a better one exists by simply taking the analog broadcast from the primary station?
Let me try it from this angle: We now know that Harris installed a turnkey HD operation for your station. We can safely assume that your HD equipment is properly chosen, compatible and correctly installed. I agree with you that it is all reasonable. The Omnia of and by itself is not an issue whatsoever in the HD sound quality. The Omnia's SETTINGS
OTOH... I am certain that a phone call to Omnia would provide a default setting to start and the counsel needed to advise you on it's correct setup for your operation. It sounds to me that your HD "artifact" problems could be as simple as a level that is slightly too high. You were presented two options. One involved using a HD signal that needs little more than a tweak for a quality feed to the translator. The other option was to settle for an expensive, jury-rigged analog feed. It appears that you decided to settle. I would have performed all tweaks possible and gone with the superior digital HD feed. My question to you is: Why should you hack and retransmit a compromised analog
signal when a better one exists by simply taking the superior HD digital broadcast from the primary station?
You and I approach the situation differently. 1st thing I would do is get the HD tweaked for clean audio. Good equipment and install here so there is no reason for less than 100% HD quality audio. 2nd I would discuss the signal issues at the next station meeting and request a morning to kill 88.5 for a couple or three hours. With 88.5 off-air I would drive the 88.3 signal and - using garden variety radios - determine just exactly what extent both 88.3's "directional" analog AND digital signals encroach 88.5's 60 dBu contour. I would drive the 88.3 contour areas where 88.5 allegedly interferes to see how 88.3 does on its own. I would then activate the 88.5 signal in analog mode only and replicate the first drive and observe 88.3's hybrid signal's effect on 88.5's analog only signal and vice versa. Finally I would kill the 88.5 analog, fire up 88.5's HD and again redrive the route. This time you determine the 88.3 hybrid/88.5 pure digital interplay over their respective coverage areas. You now know exactly what you have and where you stand on this issue.
The 88.3 upper HD sideband interferes with the 88.5 analog signal in 88.5's weaker signal areas. 88.5's lower HD sideband interferes with 88.3's analog signal in 88.3's weaker signal areas. 88.3's upper HD and 88.5's lower HD digital sidebands do not affect each other in that manner. Find a spot where 88.3 and 88.5 both provide strong signals. Both stations should lock on HD and provide perfect HD digital sound.
I understand that 88.3 and 88.5 both run HD at -14 dBc. I believe that 88.3 and 88.5 can lower their adjacent HD sidebands to -20 dBc. How did that work out?
Mechanical beam tilt for both 88.3 and 88.5 as compensation for the unique terrain between the 2 stations is another possible option.