clouseau said:
Why can a really selective radio not get the "Hash", but a cheap radio does?
The answer is (Basically) The "Hash" is not actually on the same frequency as the broadcast, it's NEAR the frequency of the broadcast and the radio can't tell the difference.
Let's look at Tom's experience below...
Tom Wells said:
Today I was working in downtown Chicago, and went over to Lake Shore Drive to go home.
The road, for those who don't know, is squished between the shore and the tall buildings of Chicago.
These buildings seem to provide both a shielding from the WLS signal, and a reflector for signals from the east (WGTO).
And I am still able hear WGTO clearly on Lake Shore Drive, as long as tall buildings are to the west.
As soon as the "view" is clear to the west and south, the WLS IBOC obliterates WGTO.
This would be a function of how good a radio you use to receive it. Now clearly Tom has a fairly decent radio to get these results from so far a distance. WGTO is 90 miles away from Lakeshore Drive. Definitly DX for a 1 KW station. however the point I'm making is (And Tom can answer this) Does WLS come in all along Lakeshore Drive? I think YES is the definitive answer. So it's not really a question of "Does WLS transmit hash on 910?" but more like "Does WLS transmit SO MUCH hash on 900 that it overloads even Tom's fairly decent radio?" I would say YES. Keep in mind WGTO is so distant..if WLS wasn't on the air in Chicago, it would most likely be possible to license ANOTHER station in Chicago on 910 IN ADDITION to WGTO. (At least based on the very limited interference you would receive from WGTO.) Also keep in mind there have been a good number of REALLY BAD radios made out there. This goes for FM too.
However, cheaper radios get splattered much worse.
Yes they do. Perhaps a better way to put that would be "Low Quality Radios are much less selective" Same difference...
Clouseau
Even before WLS added IBOC, the shielding/reflector effect at the base on Lake Shore Drive was quite pronounced.
The level of WLS is attenuated by what seems to be as much as 20 db or more in a few spots,
where Tinley Park WLS is forty miles south behind a "mountain of steel".
The reflector effect makes WGTO far stronger than on open terrain nearby, maybe 10 db.
I did put the 1925 loose vario-coupler on the 1936 Philco today.
The vario-coupler loop is a vertical loop antenna, using two loops.
The angle and phase polarity between inner and outer loops is continuously variable,
the inner loop is small and connects to balanced inputs of the radio.
The outer loop has many turns, and along with a capacitor, is reasonated at the objective frequency.
It is possible to achieve very critical directional nulls.
By luck of having 90 degree offset relative between stations, aiming the critical null at WLS leaves the broadside
sensitivity toward WGTO. Reasonating antenna at 910 gives a weak but listenable 910, with exactly the same
situation as the recording documents. It is possible to listen on the upper SB and get a clean but weak signal.
Not nearly as strong as the reflector situation on the drive.
Maybe a little hissier than before, remembering that now WOKY is directional IBOC on 920, only 55 miles off, and is audible here,
though mybe not nulled as well for the loop.
The spec calls for data to 14.? khz, and this puts WLS up to 904.?.
Bandwidth of the receiver is then everything, combined with abilty to tune 4 khz off to avoid the data.
I am considering here both the car radio and this particular Philco, which both have sharp tuning, while rewarding side tuning
of stronger signals with great crispness of high frequency info.
Naturally, narrowband radios will not hear this.
If the IF bandwidth of a modern AM car radio is 10khz, the audio out is max 5khz.
this would still only be sidebands in this instance from 905-915 khz.
But these are "unmusical" radios, for the most part.
Conclusion- Tunable external loops will be our new best friends.
WLS truly is not "on" 910. They are on 4khz of the decoding passband WGTO needs for their modulation.
Specifically 901-904 khz. IF we have a radio which can avoid these 4 khz in contention, a tunable loop antenna,
and a favorable position relationship between desired/undesired signals, it is possible to listen to 2nd adjacents of IBOCs,
even when the larger IBOC is 50 times the power and half the distance, and still have high frequency analog reproduction.
But the Philco with the tuned loop is a radio blood hound on AM MW, so thought I'd try another radio.
I went to the kitchen and tried with the GE 1982 reproduction cathedral, with a very similar result.
If tuned to the upper side band, and critically angle postioned to null WLS, even this table radio could still pull a
"weak but usuable" WGTO, again with more noise than memories of WGTO before the WLS/WOKY IBOC sandwich.
Overload is going to be an issue on the bad radios out there. Selectivity is now done at the IF stage, they seldom put a tuned
amplifier stage at the incoming frequency these days.
What works well in cheap radios to make analog signals sound good is going to make the same radios sound awful with hybrid AM
and unlikely to ever pick up such "dx", by the same lack of tuned RF stage.
And of course, it would be a trick to get a magnetic-azimuth tracking loop for AM reception in cars to permit this while driving.
Bottom line is you can get some 2nd adjacents from IBOCs, if you try hard enough.
And it's difficult to agree on appropriate bandwidths, audio or IF.
It's even difficult to agree on selective sideband tuning.
It all depends on what the user expects of the radio, and whether or not that radio delivers a particular "quality" they desire.
It may be that such quality as in high-frequency crispness is the very fruit of cheapness itself.
It's a lower-quality radio than a more selective radio, but sounds more natural in audio.
Such cheap radios will be laid low by IBOC AM, as others have also stated. (rbruce carter5)
