Selectivity vs. sensitivity

[micky]

I've known the basics of sensitivity and selectivity for a long time,
and I read more abou them on the web this week, but it hasn't helped.

I want a newer car radio for my 2005 Toyota Solara, and I live in
Baltimore and want to be able to receive WAMU, 88.5 and WCSP
(c-span)90.1, from DC.

Which value matters in predicting whether I'll be able to do so,
selectivity or sensitivity?

My current radio gets both stations, but there have been radios that
don't get stations I know exist and in that situation, there is a
general low level noise something like the wind blowing. I suppose you
have all heard it.


Alternatively, limiting what I pay to $300, maybe 400 and 500 at the
very most, what brands are "certain" to get any station my Toyota radio
gets and my Chrylser radio got in the previous 3 cars.

I'll probably buy from Crutchfield becasue they have kits to connect to
the steering wheel controls.

Mostly I want the new radio to have a USB and AUX input, and maybe
buttons instead of a touch screen. It would be nice if it played CD's
and I guess no such radio will play cassettes.


Buttons are easier to use while keeping ones eyes on the road.

OTOH, though I have very little use for GPS, the current car has it
(uses a CD for the maps) and there is no monthly charge. If on the new
radio it was a one time charge included in the price of the radio, it
might be nice to have once in a great while.

Thanks in advance.

 

You want these stations in your car ? Well, a buddy has a Ford Taurus with a radio with extreme sensitivity and doesn't exhibit that noise like older tuner due to the digital signals etc. on the carrier.

Some tuners vary the IF bandwidth with signal strength or even multipath reception. (Shotz ?) this gives you the low distortion of the wide bandwidth on better signals and limits distortion on weaker or much reflected signals.. A quite good design I say.

When you are dealing with a weak signal, narrow bandwidth is almost always the choice as noise goes up with bandwidth, and it of course affects selectivity. It affects THD especially in stereo because the sidebands are blocked. Sure, you can get by with a +/- 75 KHz bandwidth but it sounds like shit.. How picky are you ?

So you have questions that sales is not going to be able to answer here, I don't know what to tell you. Look at audiophile specs on these tuners if you can get them. the quieting curve, THD vs. signal level. No way can they quantify how it handles multipath, but that is usually less of an issue with a signal originating farther away. (unless you are in NYC itself)

So in the end, both parameters you ask are important. I tighter bandwidth will shield out local stations that are stronger. If you have them 200 KHz away you definitely need the utmost in selectivity. Sensitivity is related but shorter bandwidth will result in better quieting. Thus a tuner with shorter bandwidth will measure better in selectivity with all other things equal. I used to custom align IF strips on old tuners for that.

Another factor is that the frequencies you mentioned are at the low end of the band. that means the varactors are operating at higher capacitance and inaccuracy and drift are worse. this is almost impossible to tweak, I would not attempt it and lack the equipment to do it anyway.

As such, an in person audition ight be necessary. Go to the store whether you buy there or not and search the lower end of the FM band on various units. if you find one with really superior performance buy it, and insist on getting THAT ONE, not another one in the box. that may be the only way to do it.

Anyway, that is my take on it, take it or leave it.

 

[Jeff Liebermann]

On Thu, 07 Jun 2018 20:32:03 -0400, micky <NONONOmisc07@bigfoot.com>
wrote:

I've known the basics of sensitivity and selectivity for a long time,
and I read more abou them on the web this week, but it hasn't helped.

I want a newer car radio for my 2005 Toyota Solara, and I live in
Baltimore and want to be able to receive WAMU, 88.5 and WCSP
(c-span)90.1, from DC.

Which value matters in predicting whether I'll be able to do so,
selectivity or sensitivity?

Both, and both have complications.
For selectivity, if your FM radio can hear HD Radio (IBOC), it needs
to have an IF bandwidth of at least 400 KHz. Here's what it looks
like on a spectrum analyzer:
<http://www.learnbydestroying.com/jeffl/crud/KBRG-100_3.jpg>
<http://www.learnbydestroying.com/jeffl/crud/KCSM.jpg>
It won't work if the IF bandwidth (-3dB down) were exactly 400 KHz as
it would be clipping the corners of the IF bandpass and probably have
horrible group delay. It has to be wider, typically about 500 to 600
KHz IF bandwidth. However, even if it was 400 KHz wide, you would
still have an adjacent channel problem. In the US, FM channels are on
200 KHz intervals. That means the digital part of the spectra
overlaps the conventional analog FM part of the spectrum in the
adjacent channel. If you were listening to a conventional FM station,
and there were an HD Radio digital station on the adjacent 200 KHz
slot, its digital signal would slop into your IF bandpass and all you
would hear is digital garbage.

The closest approximation to a solution are the digital FM receiver
and demodulator chips by SiLabs.
<https://www.silabs.com/products/audio-and-radio/multi-band-radios>
The IF bandwidth is programmable and very much a brick wall. The
designers can narrow up the IF bandwidth to exactly 200 KHz which will
remove most, but not all, of the HD Radio garbage in the adjacent
channel. You'll find these chips in radios by Tecsun and Meloson. Not
sure about car radios.

So the importance of selectivity depends on what you're listening to
(conventional FM, or HD Radio) and what's on the adjacent channel.

It's almost midnight and I'm beat. I'll dive into the sensitivity
part later, when I'm more awake. Incidentally, FM receiver
sensitivity is rather oddly measured in dBf (dB above 1 femtowatt).

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Jeff Liebermann]

On Thu, 07 Jun 2018 20:32:03 -0400, micky <NONONOmisc07@bigfoot.com>
wrote:

Which value matters in predicting whether I'll be able to do so,
selectivity or sensitivity?

This looks like a tolerable explanation of what the numbers mean:

"How to select an FM tuner for 88-108 Mhz DX"
<http://home.iprimus.com.au/toddemslie/howtoselectatunerforfmdx.html>


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Look165]

selectivity is the opposite to sensivity.

jurb6006@gmail.com a Êcrit :

You want these stations in your car ? Well, a buddy has a Ford Taurus with a radio with extreme sensitivity and doesn't exhibit that noise like older tuner due to the digital signals etc. on the carrier.

Some tuners vary the IF bandwidth with signal strength or even multipath reception. (Shotz ?) this gives you the low distortion of the wide bandwidth on better signals and limits distortion on weaker or much reflected signals. A quite good design I say.

When you are dealing with a weak signal, narrow bandwidth is almost always the choice as noise goes up with bandwidth, and it of course affects selectivity. It affects THD especially in stereo because the sidebands are blocked. Sure, you can get by with a +/- 75 KHz bandwidth but it sounds like shit. How picky are you ?

So you have questions that sales is not going to be able to answer here, I don't know what to tell you. Look at audiophile specs on these tuners if you can get them. the quieting curve, THD vs. signal level. No way can they quantify how it handles multipath, but that is usually less of an issue with a signal originating farther away. (unless you are in NYC itself)

So in the end, both parameters you ask are important. I tighter bandwidth will shield out local stations that are stronger. If you have them 200 KHz away you definitely need the utmost in selectivity. Sensitivity is related but shorter bandwidth will result in better quieting. Thus a tuner with shorter bandwidth will measure better in selectivity with all other things equal. I used to custom align IF strips on old tuners for that.

Another factor is that the frequencies you mentioned are at the low end of the band. that means the varactors are operating at higher capacitance and inaccuracy and drift are worse. this is almost impossible to tweak, I would not attempt it and lack the equipment to do it anyway.

As such, an in person audition ight be necessary. Go to the store whether you buy there or not and search the lower end of the FM band on various units. if you find one with really superior performance buy it, and insist on getting THAT ONE, not another one in the box. that may be the only way to do it.

Anyway, that is my take on it, take it or leave it.

 

[John-Del]

On Thursday, June 7, 2018 at 9:20:55 PM UTC-4, jurb...@gmail.com wrote:
> You want these stations in your car ? Well, a buddy has a Ford Taurus with a radio with extreme sensitivity and doesn't exhibit that noise like older tuner due to the digital signals etc. on the carrier.

I had more than a couple of people complain that their factory Ford radio had better AM DXing range than their aftermarket radio.

I don't know about the new Fords, but Fords through the early 2000s had very sensitive and reliable factory radios.

The last Ford I had was a 2000 Explorer, and that radio could pick up WFAN and WCBS (New York AM stations) almost like they were locals. I could listen to ballgame from New York when others couldn't. Too bad Ford didn't know as much about automatic transmissions as they do about building radios.

 

[root]

John-Del <ohger1s@gmail.com> wrote:

The last Ford I had was a 2000 Explorer, and that radio could pick up WFAN and
WCBS (New York AM stations) almost like they were locals. I could listen to
ballgame from New York when others couldn't. Too bad Ford didn't know as much
about automatic transmissions as they do about building radios.

Where were you when you listened to WFAN and WCBS?

I had a 1946 Studebaker which could pick up Los Angeles radio stations
when I was in Twin Falls, Idaho.

 

[John-Del]

On Friday, June 8, 2018 at 11:21:55 AM UTC-4, root wrote:

John-Del <ohger1s@gmail.com> wrote:

The last Ford I had was a 2000 Explorer, and that radio could pick up WFAN and
WCBS (New York AM stations) almost like they were locals. I could listen to
ballgame from New York when others couldn't. Too bad Ford didn't know as much
about automatic transmissions as they do about building radios.

Where were you when you listened to WFAN and WCBS?

I had a 1946 Studebaker which could pick up Los Angeles radio stations
when I was in Twin Falls, Idaho.

Wolcott, CT (near Waterbury) - certainly in range for a decent radio, but a lot of AM radios don't get them around here. I drove my brother's 2012 BMW couple of weeks ago and couldn't listen to the Yankee game on FAN. Picked up every other word drowned in mostly static.

When I'm sitting on my back deck listening to a ballgame, I use an Emerson 911 transistor radio - circa early 1960s. Picks it up nice and clear.

https://3.bp.blogspot.com/-sP1dDxTXUbk/Tt067pJcN2I/AAAAAAAAAEo/QkDQNjW3BM8/s1600/%2524%2528KGrHqV%252C%2521jkE66tt%252BVPkBOvs91HOEQ%257E%257E60_3.jpg

 

[Jon Elson]

On Thu, 07 Jun 2018 20:32:03 -0400, micky wrote:

I want a newer car radio for my 2005 Toyota Solara, and I live in
Baltimore and want to be able to receive WAMU, 88.5 and WCSP
(c-span)90.1, from DC.

If you are really IN Baltimore, there's no way you can get DC stations on
a car radio. I lived on the Eastern Shore of VA for a while, and I did
listen to my favorite DC stations, but I built a Yagi antenna and pointed
it up into the sky. That was a fixed location and home stereo equipment,
not a car radio. That worked pretty well, but you got a lot of flutter
any time an airplane was crossing in the middle.

If you are expecting to get the info from a few specs listed on the
outside of the box, I wouldn't bother. Those specs are not likely to be
very accurate or useful by comparison.

Jon

 

[Dave Platt]

In article <pfe2lg$17p0$1@gioia.aioe.org>,
Look165 <look165@numericable.fr> wrote:

>selectivity is the opposite to sensivity.

By no means. They're almost orthogonal in principle, although in
practice they may tend to go in opposite directions.

Sensitivity is a measure of how well a tuner picks up the desired
(on-frequency) signal... that is, how weak a "wanted" signal it can
detect.

Selectivity is a measure of how well a tuner _rejects_ non-desired
signals (on adjacent channels, alternate channels, and further
away)... that is, how strong an "unwanted" signal it can filter out.

Cheap tuners may be both insensitive, and not very selective.

Really good FM tuners can be highly selective, _and_ highly sensitive.
This generally requires having at least one stage of selectivity
(i.e. one or more tuned stages) before the first RF amplifier - these
stages keep strong, off-frequency signals from overloading the amp.

Tuners that are beloved of the "FM DX" crowd will tend to have:

- Quite a few stages of selectivity in the front-end. You'll see
tuners described as having 3, 4, 5, or more "sections" in the front
end - each section is a tuned circuit. Commonly, one section tunes
the local oscillator, and the rest provide RF selectivity before
the mixer.

- Several different bandwidths available in the IF section. A narrow
IF (more stages of IF filtering, and/or more-narrowly-tuned filters
in each stage) provides better selectivity. This can be at the
cost of sensitivity (each IF filter stage adds some amount of loss,
even to the desired signal) so a good narrow-IF design will include
additional stages of IF amplification to make up the losses and
restore the sensitivity.

- Post-detection filters, after the FM detector and before the
stereo-multiplex decoder. These help filter out "birdies" and IBOC
digital sub-carrier noise, from FM stations on adjacent or
alternate channels.

 

>"selectivity is the opposite to sensivity. "

No, it is not.

 

>"Tuners that are beloved of the "FM DX" crowd will tend to have: "

I want one with continuously variable IF bandwidth on the front.

 

[Jeff Liebermann]

On Fri, 8 Jun 2018 21:47:28 -0700 (PDT), jurb6006@gmail.com wrote:

>I want one with continuously variable IF bandwidth on the front.

With a DSP filter and demodulator, you can have exactly that. Spin
the shaft encoder knob, and the filter coeficients will change to
whatever you find useful. Not exactly what you want, but close:

ATR4255P
<https://media.digikey.com/pdf/Data%20Sheets/Atmel%20PDFs/ATR4255P.pdf>
For improved FM performance, an integrated IF filter with
adjustable bandwidth, a soft mute feature, and an automatic
multipath noise cancellation (MNC) circuit are fully integrated.
A powerful set of sensors is provided for receiving condition
analysis and stop signal generation.



--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Phil Allison]

jurb...@gmail.com wrote:

"Tuners that are beloved of the "FM DX" crowd will tend to have: "


I want one with continuously variable IF bandwidth on the front.

** Such a feature is useful with AM reception but not with broadcast FM.

The FM signal is inherently wide band, with +/-75 kHz deviation at peak audio level - if the IF bandwidth is less than 150kHz, distorted sound is the result.

I have a radio scanner ( AR 1000xlt ) with wide and narrow FM modes, 30kHz and 200kHz respectively. Listening to broadcast FM while in narrow mode is *intolerable*, in wide mode it sounds just fine.



..... Phil

 

>"** Such a feature is useful with AM reception but not with broadcast FM. "

I've had it in a couple of tuners and found it useful when DXing, and once in a great while other times but still DXing somewhat. Listening to strong local stations just leave it in wide though, then it practically worthless.

 

[Phil Allison]

jurb...@gmail.com wrote:

"Tuners that are beloved of the "FM DX" crowd will tend to have: "

" I want one with continuously variable IF bandwidth on the front. "

"** Such a feature is useful with AM reception but not with broadcast FM. "

The FM signal is inherently wide band, with +/-75 kHz deviation at peak audio level - if the IF bandwidth is less than 150kHz, distorted sound is the result.

I have a radio scanner ( AR 1000xlt ) with wide and narrow FM modes, 30kHz and 200kHz respectively. Listening to broadcast FM while in narrow mode is *intolerable*, in wide mode it sounds just fine.

I've had it in a couple of tuners and found it useful when DXing,

** Continuously variable ????

Or just a couple of settings.

FFS stop oversnipping !!!!



..... Phil

 

>"** Continuously variable ???? "

Sorry, switchable, narrow and wide. I heard of a tuner with three positions but never had one and don't remember the name or model.

Doing variable control in the analog domain would be an incredible bitch but that's how I want it. Actually it only has to be a couple of stages towards the front, maybe even just one, but still. Maybe Studer Revox would do something like this (maybe they have) but I doubt anyone else. Them engineers there I bet are showoffs. I'm not bitching, just saying. I saw the print of one of their tuners and said "WTF, are you sending the first mission to Mars or what here ?". I'm sure I still have it lurking around a drive here but it would probably be easier to find it online again than to look through all my backup.

Yes I am a nasty SOB who wants someone else to do what I can't. But they get paid for that.

 

[Ron D.]

I had an 82 Toyota Celica. Radio was horrible. It looked like it was designed for an external antenna amplifier and when one was added, the number of stations received increased.

It was very "hissy" when the speakers were upgraded,

I have a 2000 Solara and the Radio is pretty nice. 5 CD changer, cassette and AM/FM.

==

House wise, I have a Technics Professional ST-9030. See http://audiokarma.org/forums/index.php?threads/technics-tuner-st-9030.363631/ I have been able to get 3 stations on the same frequency just by rotating the antenna.

The FM bandwidth is selectable from auto and wide. They probably should have made it auto and narrow. It may continuously change bandwidths in auto mode.

To make things more interesting, I added a Carver TX1-11 signal process which makes multipath noise "go away".

More interesting yet, I have a 4bx dynamic range expander with impact restoration.

The tuner had two outputs. One filtered at 15 kHz so it would not interfere with tape decks and one with a higher response.

I also owned a automotive Blaupunkt Tucson which was very good coupled with an active AM antenna.

 

On Sunday, June 10, 2018 at 12:35:38 PM UTC-5, Ron D. wrote:

I had an 82 Toyota Celica. Radio was horrible. It looked like it was designed for an external antenna amplifier and when one was added, the number of stations received increased.

It was very "hissy" when the speakers were upgraded,

Ford and GM seemed to apply importance to their car stereos in the early 1980s. Amps with DPL (anti-clippping gain control), speakers from Bose, tuners from Hughes Aircraft which were also used in David Hafler tuners, and Blaupunkt for the cassette decks. Bose also made some amps for mainly Caddilacs, they were class D and ran into very low impedance. But that was no stranger to Bose, the speakers in the 901s are 0.9 ohms each. They get near 8 ohms being all in series.

And a buddy of mine has a 2005 Ford Taurus and that thing gets stations I can't even dream of getting. Two of them I really want, 94.9 and 97.5 out of Akron, which is not all that close. And he gets them clean. I might have to fell him over this. (jk)

House wise, I have a Technics Professional ST-9030. See http://audiokarma.org/forums/index.php?threads/technics-tuner-st-9030.363631/ I have been able to get 3 stations on the same frequency just by rotating the antenna.

The FM bandwidth is selectable from auto and wide. They probably should have made it auto and narrow. It may continuously change bandwidths in auto mode.

I ould like auto, narrow and wide if I can't have a variable control. In fact I wouldn't mind auto because signal conditions change.

To make things more interesting, I added a Carver TX1-11 signal process which makes multipath noise "go away".

I bet all that is is a stereo blend with logic. Bob did alot of "magic" that way. Those asymmetrical charged coupled device tuners of his were not the cat's ass. All it did was to detect what it thought was distortion along maybe with multipath which is easy to detect and start blending left and right and adding a digitally delayed signal to the L-R.

More interesting yet, I have a 4bx dynamic range expander with impact restoration.

I am going to build something like that one day if I live long enough, and all in discrete components.


> The tuner had two outputs. One filtered at 15 kHz so it would not interfere with tape decks and one with a higher response.

Regular FM stereo is capable of 19 KHz but it takes some doing. It takes a very accurate pilot cancel circuit with a PLL generated null signal to assure a perfect sine wave. Interference to the wave would be reproduced, but also prevented from interfering with the phase lock of the MPX decoder oscillator. I don't want the job, maybe Revox.

> I also owned a automotive Blaupunkt Tucson which was very good coupled with an active AM antenna.

Seems like you're into AM. Well, it is more people's media because it is much cheaper to have an AM station than FM, and forget TV. Maybe, for the common good we should support AM radio.

I'll have to give that some thought.

 

[Jeff Liebermann]

On Sat, 9 Jun 2018 18:02:00 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

jurb...@gmail.com wrote:
I want one with continuously variable IF bandwidth on the front.

** Such a feature is useful with AM reception but not with broadcast FM.
The FM signal is inherently wide band, with +/-75 kHz deviation at peak audio level - if the IF bandwidth is less than 150kHz, distorted sound is the result.
I have a radio scanner ( AR 1000xlt ) with wide and narrow FM modes, 30kHz and 200kHz respectively. Listening to broadcast FM while in narrow mode is *intolerable*, in wide mode it sounds just fine.
.... Phil

A bit of hair-splitting here. The FM channel allocation in the USA is
at 200 KHz intervals. However, if one adds the digital (HD Radio,
IBOC, iBiquity, etc) modulation, the bandwidth is now 400 KHz wide:
<https://en.wikipedia.org/wiki/In-band_on-channel>
This is what it looks like on a spectrum analyzer:
<http://www.learnbydestroying.com/jeffl/crud/KBRG-100_3.jpg>
<http://www.learnbydestroying.com/jeffl/crud/KCSM.jpg>

In most HD Radio receivers, the IF bandwidth is set by a digital
filter. For conventional FM, it's 200 KHz wide. For digital FM, it's
400 KHz wide. I suppose it could be front panel set by the user, but
methinks it makes more sense to have the IF bandwidth automagically
set by the mode and sub-channel.

Measuring Your IBOC Spectrum
<http://www.nautel.com/wp-content/uploads/2011/08/NAB-Measuring-Your-IBOC-Spectrum-David-Maxson.pdf>

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558