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This Curious Phenomenon

Ai4i

Ai4i

Star Participant
I am so used to digital components dropping out while the analog is still very listenable
that this experience caught me off guard:
A station is unlistenable multipath distortion throughout the living room,
but as soon as the receiver locks onto the HD part of the signal,
it's HD-1, 2, and 3 remain locked in perfectly throughout the room.
 
A local country stations tends to do maintenance overnight late on Sundays or early Mondays and they always shut the big 100 kW transmitter off… but leave the HD on. It's weird going from complete static to perfect signal in seven seconds.
 
I've experienced the same "phenomenon" as you mentioned. I've even had a weird DX'ing experience while listening to an AM station over 1000 miles away. Out of the blue the HD light came on, locked and the station got completely clear. It stayed like that for nearly 20 minutes until eventually it faded away.

And there inlies that truth of digital. When it's threre, it's there. As long as the one's and zero's make it to their intended destination without too many re-transmits you're golden. :)
 
It happened last night I picked WWRZ 98.3 from Lakeland and was able to get all three HD channels on that frequency. I live in St.Pete near Gandy Boulevard. Easily 50 miles from where the tower is. I guess it was a good night to go HD surfing.
 
Tea Men said:
It happened last night I picked WWRZ 98.3 from Lakeland and was able to get all three HD channels on that frequency. I live in St.Pete near Gandy Boulevard. Easily 50 miles from where the tower is. I guess it was a good night to go HD surfing.
Click to expand...

"HD Surfing" - You should copyright that. :)
 
stewie said:
I've experienced the same "phenomenon" as you mentioned. I've even had a weird DX'ing experience while listening to an AM station over 1000 miles away. Out of the blue the HD light came on, locked and the station got completely clear. It stayed like that for nearly 20 minutes until eventually it faded away.

And there inlies that truth of digital. When it's threre, it's there. As long as the one's and zero's make it to their intended destination without too many re-transmits you're golden. :)
Click to expand...

Which station was it, Stewie? As I live in the West, I'm just curious. 1000 mi from Sacramento could be KSL or possibly a station in AZ?

My Sony XDR will show the HD indicator blinking on KSL, but so far, no HD has come through.
 
boombox4 said:
Which station was it, Stewie? As I live in the West, I'm just curious. 1000 mi from Sacramento could be KSL or possibly a station in AZ?

My Sony XDR will show the HD indicator blinking on KSL, but so far, no HD has come through.
Click to expand...

You got it, KSL it was. Hasn't happened since but to be honest, I don't try very often. Wish I had a Sony XDR though. :)

I tuned KSL on a Pioneer "Super Tuner" (if they still call it that) in my truck.
 
The advantage to HD is the separate digital signal can handle multi path better than analog. So as long as the digital can decode it will stay locked. Now I have one for you that was strange. There was a station that had an issue for 2 weeks were the receiver would switch to the HD signal and never go back to the analog. I understand this with HD2,3,4 etc but this was HD1. When the HD faded audio would go silent and just buffer. I would have tune up/down or turn HD off/on to hear audio again. It is the lowest rated station in market so no one cared.
 
WJPYFM said:
The advantage to HD is the separate digital signal can handle multi path better than analog. So as long as the digital can decode it will stay locked. Now I have one for you that was strange. There was a station that had an issue for 2 weeks were the receiver would switch to the HD signal and never go back to the analog. I understand this with HD2,3,4 etc but this was HD1. When the HD faded audio would go silent and just buffer. I would have tune up/down or turn HD off/on to hear audio again. It is the lowest rated station in market so no one cared.
Click to expand...

Believe it or not, I've encountered a station that did that same thing, but I can't for the life of me remember where it was.
 
I find it fascinating during tropo when local 99.5 WBAI out of New York, locks in WJBR out of Wilmington, DE's HD signal. What's interesting is I'll continue to hear WBAI for about 10 seconds after the HD lock and then WJBR just comes in crystal clear and the side channels are there as well! WBAI is only 10 miles East, from my location.

I imagine a lot of the same phenomenon happens daily, throughout Central New Jersey with 100.3 and 101.1 sharing a frequency with New York and Philadelphia.
 
WJPYFM said:
The advantage to HD is the separate digital signal can handle multi path better than analog. So as long as the digital can decode it will stay locked. Now I have one for you that was strange. There was a station that had an issue for 2 weeks were the receiver would switch to the HD signal and never go back to the analog. I understand this with HD2,3,4 etc but this was HD1. When the HD faded audio would go silent and just buffer. I would have tune up/down or turn HD off/on to hear audio again. It is the lowest rated station in market so no one cared.
Click to expand...

That's a setting in the station HD Exporter. If they're using a Nautel Exporter, there is a tab in the setup firmware which comes from the factory as (to paraphrase): "Tell receiver to stay in digital mode". (factory default) There is a check box on that same tab where the exporter gives the receiver permission to return to analog if the digital signal is unstable.

I could tell our local NPR station replaced their Exporter, forgetting to check that box when installed because my HD radios wouldn't go back to analog when the HD reception wasn't holding up. I sent the CE several E-mails, even giving him screen shots of the page, tab, and box to check, but it took them about two months before they either read my E-mail, or finally figured it out.
 
Last edited:
We use HD on our LPFM. Listeners tell us about that benefit a lot. LPFM stations, with low antennas and low wattage, can really be plagued with multi-path interference in various tiny spots in town. A listener in a car could stop at a light and experience a degraded analog signal -- move up a few inches and it's back again. However, with our HD1 there is much less of that phenomenon. It actually maintains a "lock" where the analog signal fails.
 
But does the LP HD go more than 2 or 3 miles in a car?
 
ai4i said:
But does the LP HD go more than 2 or 3 miles in a car?
Click to expand...

It generally matches our service contour - depending on the listener's car and radio, though I've never experienced it going past our analog signal. Where it seems to excel is in resisting multi-path.

I'm not an engineer, but I believe receivers use both the upper and lower HD Radio side-bands as an added redundancy. That my uninformed guess.
 
Ralph Martin said:
...I believe receivers use both the upper and lower HD Radio side-bands as an added redundancy...
Click to expand...
It would be nice if someone had thought of delaying one set of sidebands more than the other,
so listeners in moving vehicles would benefit from frequency, time, and spatial diversity.

It must be expensive for an LPFM to be able to transmit HD;
How much HD power is a 100 watt FM at 100 feet allowed to put out,
and is it the same for all stations?
 
My understanding of the HD technology is that there is some sort of time delay redundancy at play on the digital sidebands. If there wasn't, any little dropout that the error correction could not fix would result in a dropout.

As far as I know the limit for HD transmission power is 6% of the main analog signal, so that'd be… 6 watts for a 100 watt LPFM? Yikes.
 
The HD ERP power for a LPFM would be between 10 and 4 watts depending on 1st adjacency spacing. (4 to 10 percent of analog power.)
 
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