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Skip wipes out HD

R

rbrucecarter5

Guest
The Gulf Coast FM skip season began pretty much on schedule this morning. From Houston, the usual targets in Austin, San Antonio, and Victoria. The skip also wiped out almost all local Houston HD. Yet another consequence of putting the sidebands on adjacent frequencies.
 
Have you ever gotten any HD DX? I've experienced it a few times, mostly just the PAD decoding call letters, which RDS can do without as much fanfare. But at least on one occasion, I got one of the Albuquerque stations in rock solid HD for several minutes whilst in Mississippi. (A few months later I was actually in Albuquerque and couldn't get that station to decode reliably to save my life.)
 
I once had an analog FM station "hijacked" by an HD Radio decoding a completely different station's HD data on the same frequency. It was interesting to listen to it blend back and forth between analog station #1 and digital station #2, on the same frequency. The receiver was also showing station #2's info on the display even when it was receiving station #1's analog audio.
 
The Jersey Shore should be a good test for cochannel between Philly stations to the Long Island stations.

The density of the Ocean frequently wreaks havoc with FM.

Can't wait to find out this Summer...

Jeff in Sa-ra-so-ta!
 
satech said:
I once had an analog FM station "hijacked" by an HD Radio decoding a completely different station's HD data on the same frequency. It was interesting to listen to it blend back and forth between analog station #1 and digital station #2, on the same frequency. The receiver was also showing station #2's info on the display even when it was receiving station #1's analog audio.
Click to expand...

Yes that happens quite a bit on my Sony XDR-F1HD. I have three locals or semi-local analog FM's that, if I point the antenna toward them, they are 100% clean. But if I aim toward the co-channel HD on a decent Tropo day, it can be quite the listening experience.

My affected FM's are

Local analog 88.9 WDNA vs HD WQCS
Local analog 89.7 WKCP vs HD WUSF
Local analog 107.9 WEAT vs HD WSRZ

Was even blessed last year to have semi-local WVUM 90.5 overridden, by one split second, XEDA Mexico City with HD 1 & 2.

cd
 
After KIXS had to downgrade in Victoria for KQQK, I often get KQQK's HD signal over KIXS. What I like best about the HD-1x tuner I can disable the HD part and have all analog. When KSBJ took over 96.9 in Bay city they cut the HD off.
 
It hasn't happened to me yet, although Seattle isn't exactly the FM DXing capital of the world.
I believe that last year's reception of KJZZ-91.5 from Phoenix fel only a decibel or two short of rendering 91.3's HD unusable.
We don't have very many frequencies to work with, so if something comes in on its main frequency, the HD sidebands are likely covered by locals.
The DX also isn't as intense here as in other parts of the country.
Thus, so far I haven't logged any HD audio via skip.
But I'll keep trying on the few frequencies that remain. If I succeed and I capture the audio, I'll post a link to it.
 
^ If TX was caught from OH, especially for 1 minute, that had to be E-skip, not Tropo. Oh Tropo is possible, but it would have to be super duper, especially over a land path. But, getting the HD to decode is pretty good!

cd
 
I heard that if you're listening to AM HD in the car and slam on the brakes, that HD decode drops.
Is this true? I'm not going to try it in our Hyundai, which would probably roll, but maybe someone in a BMW should try this for
us. It sounds like a problem with interference form the ABS braking system.

A field service guy on a visit where I work made this claim.

So not only does skip wipe out iboc, skid does, too.
 
My Chrysler ABS even slows down the defrost blower when it's activated, so I don't know if that's by design or because it takes that much electrical power to actuate all the ABS solenoids or computing power of the processor? It's very noticable though - I'll have to see what it does with the radio next time its slippery out.
 
I know there's a lot of data analysis going on in the ABS, and there's certainly a lot of pulse modulation going to the
brake pressure modulator, but I can't see why so much noise would go into the 12 volt source, or be be passed through
to the radio.....maybe whatever does the pulsation is somehow not "grounded" close enough to a common DC ground with the radio in that particular car. I also wonder if the ABS modulator had any kind of filtering
( capacitor bypassing or choke/capacitor combination.)
If it's just raw 13.8v power to the modulator, it can probably kick back enough noise to do this, but then
I wonder if the overall shielding/filtering in maybe just this one car had a problem.
Maybe the radio just had a bad rf ground, and there was a lot of noise in all the AM anyway.

I just may call him up and find out what kind of car he was driving, and a few other questions.

Now that I think about it, our Hyundai only as HD (a Kenwood), but no ABS, so I can't check anyway.
 
My outboard Sirius/XM (plugged into 12V adapter) seems to do the same thing when I brake. But it does not have to be braking fast either.
 
Tom Wells said:
I know there's a lot of data analysis going on in the ABS, and there's certainly a lot of pulse modulation going to the
brake pressure modulator, but I can't see why so much noise would go into the 12 volt source, or be be passed through
to the radio.....maybe whatever does the pulsation is somehow not "grounded" close enough to a common DC ground with the radio in that particular car. I also wonder if the ABS modulator had any kind of filtering
( capacitor bypassing or choke/capacitor combination.)
If it's just raw 13.8v power to the modulator, it can probably kick back enough noise to do this, but then
I wonder if the overall shielding/filtering in maybe just this one car had a problem.
Maybe the radio just had a bad rf ground, and there was a lot of noise in all the AM anyway.

I just may call him up and find out what kind of car he was driving, and a few other questions.

Now that I think about it, our Hyundai only as HD (a Kenwood), but no ABS, so I can't check anyway.
Click to expand...

It just goes to show - analog design is a dying art. Nobody knows how to design a passive power filter any more, and even if they did it would add a few cents to the cost of a car, so that would be out. Car electrical systems are a joke, massively conflicting CAN Bus problems, ring networks that go down if one of 75 microcontrollers gets locked up. Nobody bypasses components on PC boards properly, assuming the PC board layout person was actually knowing what they were doing and not a glorified artist. Don't even get me started on the selection of transistors and op amps, and RF components. You better hope they actually bothered to prototype the system before then started a production run, just trusting the application circuit on the data sheet.
 
I've been griping for years about function-block design where nobody bothers to care what is going on inside the
spec'ed function blocks. My favorite is when a solid-state output device feeds a solid state input device, and no "real"
load exists to draw down the output.
Then high-impedance input cannot recognize the "off" state because the output leakage of the device never goes low enough
for the input to recognize the "low" data state.

Total fail, but thats's what happens when designers never actually had to build anything for themselves,
or troubleshoot problems in cobbled-together systems.
 
Tom Wells said:
I've been griping for years about function-block design where nobody bothers to care what is going on inside the
spec'ed function blocks. My favorite is when a solid-state output device feeds a solid state input device, and no "real"
load exists to draw down the output.
Then high-impedance input cannot recognize the "off" state because the output leakage of the device never goes low enough
for the input to recognize the "low" data state.

Total fail, but thats's what happens when designers never actually had to build anything for themselves,
or troubleshoot problems in cobbled-together systems.
Click to expand...

My favorite was in the early days of DSP design. An engineer next to me was going crazy, after spending a thousand dollars (in late 1980's dollars) for the first silicon of a DSP - his code size kept getting bigger and bigger because he said he needed more filtering. This went on for a couple of weeks, until I offered my help. It turns out he was trying to implement an anti-aliasing filter in the DSP, and always needed an additional filter to anti-alias the added anti-aliasing filter he just added. I got out a resistor and capacitor and put it on the input of the device - solved his problem completely. I was hailed as a hero! His code size shrank to half its size, as needless DSP anti-aliasing filters were deleted.

I like to invoke a job interview I went on about 15 years ago. They wanted me for car radio design. The cobbled together messes I saw in the lab were discouraging - not a trace of system level savvy. Poor PC board layout, and their only solution was to make the AM section less sensitive so it wouldn't pick up trash from every digital device on the board. This was pre-HD, I can only imagine how bad it has gotten since then. Fast forward 15 years - different manufacturer. Radio includes HD, bluetooth, satellite support, digital display, Pandora, USB MP3 support, iP____ support. Hottest AM section since Delco in the late 1960's - with a 31 inch whip! Hot FM section, picks up an FM 170 miles away clear enough to be on my presets. Manufacturer is Pioneer. If they can do quality analog / RF design, anybody can. There are no excuses!!!! The people I interviewed with - well I don't want to get sued, but they make ALL the car radios for a major auto maker. They didn't hire me, I talked too much about how to properly use bypass capacitors and how to properly do board layout. Probably stepped on some toes. And I had the audacity to go the posted speed limit when they asked me to drive them to lunch, instead of speed so they could get back to the office a few minutes earlier. I went on to be hailed as an analog expert at TI for - among other things - proper PC board layout and proper decoupling techniques: http://www.ti.com/lit/an/slyt166/slyt166.pdf, http://www.ti.com/lit/an/sloa069/sloa069.pdf
 
Interesting read Bruce; here I always thought I'd just slap a 0.1uF cap from Vcc to Gnd and I was done - didn't realize it was more of a lost art. As Artie Johnson would say: "Verrrry Interesting".
 
JohnnyElectron said:
Interesting read Bruce; here I always thought I'd just slap a 0.1uF cap from Vcc to Gnd and I was done - didn't realize it was more of a lost art. As Artie Johnson would say: "Verrrry Interesting".
Click to expand...

That's a throwback to old 5 tube All-American AC/DC radio design where the electrolytic filter cap was also the RF bypass for all the
rf and if circuits. It worked until the cap got old, then the radio would develop funny squeals while tuning.
This happened in a race to use the fewest parts possible. We're talking 1940s-50s cheapie table radios.

In good design, each section of the circuit has its own rf bypassing right at the supply to the active components.

In fact one of the cheap fixes for such old sets was to slap a .01 mfd right across the electrolytic filter cap.
If it was not humming due to poor 60 hz filtering, the .01 would stop the squeals, and the customer was happy for a few bucks.
 
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