Sensitivity rating of HD radio

[Len14043]

I have been DXing for the past 20 years and have a question about the sensitivity on a HD radio I am considering purchasing. I read about the pros and cons about IBOC and consider myself neither an advocate nor opponent. However, I am curious on how they operate and am considering purchasing a HD radio from Radiosophy. Before I spend $250 on a unit which may become obsolete within a few years, I would like to make sure that the radio will still be good for analog DXing. I see the sensitivity expreessed in several ways when comparing radios. The Radiosophy radio is rated at -84dbM for AM and -88dbM for FM. I am curious on how that compares with good DXing radios such as the GE Superradio and the CC Radio Plus. Thank you in advance.


You can view the radio at the link below:

http://www.radiosophy.com/

 

[1290wgli]

> I have been DXing for the past 20 years and have a question
> about the sensitivity on a HD radio I am considering
> purchasing. I read about the pros and cons about IBOC and
> consider myself neither an advocate nor opponent. However,
> I am curious on how they operate and am considering
> purchasing a HD radio from Radiosophy. Before I spend $250
> on a unit which may become obsolete within a few years, I
> would like to make sure that the radio will still be good
> for analog DXing. I see the sensitivity expreessed in
> several ways when comparing radios. The Radiosophy radio is
> rated at -84dbM for AM and -88dbM for FM. I am curious on
> how that compares with good DXing radios such as the GE
> Superradio and the CC Radio Plus. Thank you in advance.
>
>
> You can view the radio at the link below:
>
> http://www.radiosophy.com/


For $250, it better have a decent tuning section... but I don't think I would waste my time with it. I would wait for the Boston Acoustics radio if you *really* want a listen to HD. Looks like it's constructed a little better and if the analog section is anything like the original version, it'll have a fairly good FM section with a muddy and predictable AM section.

 

[pianoplayer88key]

> For $250, it better have a decent tuning section... but I
> don't think I would waste my time with it. I would wait for
> the Boston Acoustics radio if you *really* want a listen to
> HD. Looks like it's constructed a little better and if the
> analog section is anything like the original version, it'll
> have a fairly good FM section with a muddy and predictable
> AM section.
>

IMHO, ANY radio over $15 that has a muddy sounding AM section had BETTER make up for it with absolutely SPECTACULAR adjacent-channel selectivity. (and anything over $40 should also be very sensitive - about like using a Sony SRF-42, SRF-A1, SRF-A100, etc, with one of Bruce Carter's large loop antennas, using only said radio's internal antenna.) For example, within 1/10th of a mile of a 50kW station on the west coast, with a sufficiently sensitive longwire (wideband) antenna, you should be able to CLEARLY hear a station on a split adjacent channel (< 10 kHz spacing) from Japan/Australia/Asia without ANY audible chatter from the local station, when the local station and the cross-Pacific station are the same direction.
And, for example, if you're tuned to 640 KFI while standing near the base of their tower (whenever they get a new main tower up), you might hear a LITTLE bit of chatter from KFI on 650, but KENI and WSM should each (at night, on average) be at LEAST 40dB above KFI's chatter.

 

[rbrucecarter]

HD radios will suck for AM DX'ing. In order to accomodate the HD signal, they have to have an IF wide enough for the digital sidebands. This will also be an IF wide enough to allow 2nd and 3rd adjacent stations through.

As far as trendy radios like Boston acoustics - my GE SR-3 will run rings around them when it comes to DX.

 

[tpt]

suspect the same would be true for FM, again to have a wide enough IF to accomodate the sideband IBOC signal.

 

[awj223]

tfc: Do you know of any car radios that have the type of adjacent channel selectivity you speak of? (can hear a distant station adjacent to that of a tower you're standing next to). Can this even be done without using some kind of SSB?

> IMHO, ANY radio over $15 that has a muddy sounding AM
> section had BETTER make up for it with absolutely
> SPECTACULAR adjacent-channel selectivity. (and anything
> over $40 should also be very sensitive - about like using a
> Sony SRF-42, SRF-A1, SRF-A100, etc, with one of Bruce
> Carter's large loop antennas, using only said radio's
> internal antenna.) For example, within 1/10th of a mile of a
> 50kW station on the west coast, with a sufficiently
> sensitive longwire (wideband) antenna, you should be able to
> CLEARLY hear a station on a split adjacent channel (< 10 kHz
> spacing) from Japan/Australia/Asia without ANY audible
> chatter from the local station, when the local station and
> the cross-Pacific station are the same direction.
> And, for example, if you're tuned to 640 KFI while standing
> near the base of their tower (whenever they get a new main
> tower up), you might hear a LITTLE bit of chatter from KFI
> on 650, but KENI and WSM should each (at night, on average)
> be at LEAST 40dB above KFI's chatter.
>

 

[pianoplayer88key]

> suspect the same would be true for FM, again to have a wide
> enough IF to accomodate the sideband IBOC signal.
>

I was referring to standard analog radios, and HD radios in analog mode, not in HD mode.

Also, unfortunately, I don't expect to be able to hear WBAP at noon while standing next to KMXE's transmitter.
However, I DO expect (while using a radio whose audio bandwidth is muddy, like 3 kHz, for example) to be able to hear KMXE while next to WBAP's transmitter (or is WBAP running IBOC now, too?)

And, I DO expect in HD mode to be able to hear KOGO while as close as 1/4 mile from KAVL's or KTIE's transmitter, at full bitrate, with KAVL/KTIE performing an "eclipse" of KOGO.


Graph of IF filter specs that should be in radios with limited audio bandwidth (3kHz used as an example):

0dB + -----------------
-3dB + /
-6dB + |
-12dB + |
-24dB + |
-48dB + |
-72dB + |
-96dB + |
-120dB + |
-144dB + |
-192dB + |
-240dB + -------------------------------------/
-300dB +----+----+-----+----+----+----+----+----+----+----+
-10kHz -5kHz 0kHz

symmetrical on both sides.

I hope it appears correctly, but if not, basically 3kHz should be -3dB, 3.5 kHz should be -240 dB and staying there indefinitely.

WHY DOESN'T IT INCLUDE THE SPACES I PUT IN IT? I'M NOT USING WEBTV!!!

 

[k9ez]

> suspect the same would be true for FM, again to have a wide
> enough IF to accomodate the sideband IBOC signal.
>


BZZZZZZZZZZZZZZZZZZZZZZT Thanks for playing.

My HD Radio stays tight in the analog mode. AM analog offers typical AM response, somewhere around 6 kHz I imagine. My factory Ford AM Stereo receiver is still the most "awesomest" receiver. Nice and wide but sharp enough to do soem decent DXing. And AM Stereo to boot.

FM the same.

Perhaps it is like the AM stereo days..... the receiver senses the AM Stereo signal and opens up the IF. Likewise with the HD Radio receiver.

 

[1290wgli]

> tfc: Do you know of any car radios that have the type of
> adjacent channel selectivity you speak of? (can hear a
> distant station adjacent to that of a tower you're standing
> next to). Can this even be done without using some kind of
> SSB?
>

Only car radios made my Fujitsu Ten (Eclipse) have decent AM sections that can do something close. It is fairly selective and pretty sensitive when compared to what else is out there. ALL of the other brands (Sony, Kenwood, Clarion, JVC, Panasonic, Sanyo, Alpine etc) have horrible front ends for AM.

The Eclipse is not as bright as other AM sections, so with sensitivity and better selectivity, there is a tradeoff. But I can drive in Queens and hear LI AM's and WTIC and WBZ with the Eclipse where, on other car stereos, these stations are washed (or images of other local strong stations pop up) as the recievers go into overload.

As far as picking out stations when you're right on top... I don't think there is an AM tuner design that is THAT good. Most will overload one way or the other.

 

[westlife]

> However, I DO expect (while using a radio whose audio
> bandwidth is muddy, like 3 kHz, for example) to be able to
> hear KMXE while next to WBAP's transmitter (or is WBAP
> running IBOC now, too? )

> And, I DO expect in HD mode to be able to hear KOGO while as
> close as 1/4 mile from KAVL's or KTIE's transmitter, at full
> bitrate, with KAVL/KTIE performing an "eclipse" of KOGO.



Hey buddy... don't you ever begin to think you're expecting WAY too much?

> I hope it appears correctly, but if not, basically 3kHz
> should be -3dB, 3.5 kHz should be -240 dB and staying there
> indefinitely.

While such a filter would theoretically be possible to generate with DSP, 1.) the proceessing power needed by it would be tremendous, and 2.) it would "ring" like all hell!



> WHY DOESN'T IT INCLUDE THE SPACES I PUT IN IT? I'M NOT
> USING WEBTV!!!


If you want the spacing of what you type to be preserved, surround it
with <PRE> and </PRE> tags... just like I did for this chart:

<pre>_1_ _2_ _3_ _4_ _5_ _6_ _7_</pre>


<P ID="signature">______________

</P>

 

[awj223]

Car radio selectivity

> Only car radios made my Fujitsu Ten (Eclipse) have decent AM
> sections that can do something close. It is fairly
> selective and pretty sensitive when compared to what else is
> out there. ALL of the other brands (Sony, Kenwood, Clarion,
> JVC, Panasonic, Sanyo, Alpine etc) have horrible front ends
> for AM.
>
> The Eclipse is not as bright as other AM sections, so with
> sensitivity and better selectivity, there is a tradeoff.
> But I can drive in Queens and hear LI AM's and WTIC and WBZ
> with the Eclipse where, on other car stereos, these stations
> are washed (or images of other local strong stations pop up)
> as the recievers go into overload.

Aren't the closest local stations (in Queens) to WTIC and WBZ only second adjacents (WINS, WEPN, WHLI)?

My OEM receiver has no trouble with second adjacents. I can hear KCBS/740 just fine, even though 50 kW KFMB/760 is only 10 miles away AND directional toward my area.

However, when I'm listening to KNBR/680, the same receiver does a poor job rejecting noise from XETRA/690, 30 miles away. It's listenable most of the time, but the chatter is extremely annoying.

Given what you've said about what the Eclipse can do in Queens, I'm still not convinced that it is selective enough. The benchmark I'm comparing to is my Sony ICF-SW7600GR portable. This one IS selective enough to get rid of the chatter completely, but doesn't work well in the car because of the car body acting like a giant Faraday cage.

 

[pianoplayer88key]

selectivity curve of IF filter that should be in a radio with 3kHz analog response:
<PRE>
0dB +-----------
-3dB | |
-12dB | |
-24dB | |
-48dB | |
-96dB |
-144dB | |
-180dB | |
-240dB | -------
-300dB +---+---+---+---+---+
+/- 0 1 2 3 4 5KHz
</PRE>