NA - FM Reception - NA

[Skip Miller]

I have a Bose Wave Radio - the small table top model. The FM station we listen to the most has moved its transmitter further away, and moved up the dial from 96.3 to 105.1. (I think I have the freqs correct, but if not, they are close.) The reception is now really bad.

I have tried an external dipole antenna and also an external antenna that is rectangular in shape. Brand name Terk; billed as an AM/FM antenna. (separate leads for AM and FM) Neither is any improvement.

How can I tell if my problem is multipath reception, or a weak signal? Next step I think would be a powered antenna amplifier but if the problem is multipath that won't help.

Thanks in advance for your advice.

-Skip

 

[ScottM]

How can I tell if my problem is multipath reception, or a weak signal?

If by "multipath" you mean multi-path fading then all you need to do is move the antenna a couple of feet. If the signal improves then it is likely a multi-path fading problem. While Bill is correct that the frequency change will change the fading characteristics I doubt it has anything to do with what you are experiencing. Most terrestrial propagation from near ground mounted antennas is by multi-path.

But based on what Bill said my money is on the signal is just too darn weak. You could also try a signal booster. http://www.amazon.com/Metra-44-UA60-Signal-Amplifier-Bypass/dp/B0002IEDBW

Or better yet go to an external to the house direction antenna. If you still have a TV antenna these often also had the FM broadcast band covered in them and would be an excellent antenna.

 

[kgruber]

Forget FM just click here:

 

[Skip Miller]

WQXR. Sigh. They didn't move, they reduced power.

They are now stating that the broadcast is coming from Newark, but that is probably the studio, not the antenna.

Since the signal should be cut in half to 2/3 using standard propagation models, unless you are in the fringes

No... 33rd street to 86th street... less than 3 miles!

the problem is most likely multipath The new frequency causes different multipath characteristics.

The old and new antenna site in the Empire State building, and the antenna is a shared antenna on the spire atop the building.

I'd start with some kind of outside, directional antenna pointed toward Empire, and a coaxial cable feed from the antenna to the radio. A real PITA, but the best shot at curing the issue.

I understand, but that's probably not going to happen. If this proves to be unsolveable with radio propagation, I may have to default to internet signal feed.

Thanks! -Skip

 

[ScottM]

Depending on where he lives. If he's in the 5 boroughs or close thereto, it should be sufficient signal strength. Even coming from Empire State, multipath is wicked in NY (BTDT and know it personally...). You can do a DF on two signals coming from the same antenna and find that there will be a 30-40 degree difference (BTDT, too) - even on AM (from the top of the old WTC, I had a DF bearing 45 degrees apart for WCBS 880 and WNBC 660 - and they're diplexed into the same transmit antenna on City Island).

If he's out in Nassau or Suffolk, it's probably signal strength, perhaps coupled with multipath. And moving a few feet might not cure it - there are enough reflections even close in to make it really bad over a fairly large distance.

It's also possible that the signal on the old frequency was being received as a reflection off something else and the weaker signal has reduced that in greater proportion to the direct signal or another reflection.

Again, IME, starting with a directional antenna pointed toward Empire or the strongest reflection would probably improve things.

The other thing I *might* try (as long as you can return it) is a new HD/digital radio - the digital may pick some stuff out of the noise and improve things. It'll either work or not.

Multipath at those frequencies is not going to cover a large area, only a few feet. You may get into another multipath, but more likely if the signal strength had stayed the same the issue would actually be signal blocking. With the small amount of frequency change that he has noted, if signal strength had stayed the same, a simple movement of the antenna by a couple of feet would put him out side of the fade vector.

But you said there was an almost 2/3 decrease in signal strength. Radio field strength decrease in power at a 1/r2 rate. That would mean if you increase the distance from the station by 2 you signal strength decreases by a factor of 4. Or in the case had the signal strength at the antenna decreased by half then he is receiving a quarter of the power he had been hearing.

 

[ScottM]

In rural and suburban areas, yes, in NYC and the Bay area, no.

Signal strength is part of it, but destructive multipath interference is another. Skip lives 3 miles from Empire State. With the power level and elevation involved, the signal strength will still be >85 dBu. Typical FM receivers are sensitive to about 50 dBu.

And that can be simple signal path blockage due to buildings.

I did this for a living in NYC. Weak signal exacerbates multipath - but I also qualified my statement that it depends on where he lives.

I do this for living still to this day and in urban areas much more difficult from propogation standpoint than New York. Try moving VHF signals around Hong Kong. You have topography, construction, talk buildings, water, etc. to deal with. I am not saying that multi-path is not a problem, but at the wave length of FM broadcast, roughly 3m the multi-path blockage is not wide spread. Movement of the antenna by a few feet will over come it. Now if you have weak signal movement to a new area of coverage will be necessary.

I'll bet there is somewhere in the residence where the radio will work, but it isn't going to be easy.

If it is alone fading problem due to multi-path. I suggested the movement of the antenna in my very first post.

I just looked at the power differential. It's a 6 dB difference.

Ho did you calculate this and is at ERP of 6dB? Are you looking at the receiver and how did you measure noise floor? You need to be able to calculate the SINAD at the RX input.

Given the strength of the other signals coming off Empire, a broadband signal booster will cause more problems than they'll solve: you'll end up with intermod in the booster.

Generally true and these cheap ones for the FM band can be notioursly bad. But it may be worth a try.

A tuned booster will avoid some of that, but most FM boosters aren't going to reject the other signals. (In fact, there might be an intermod issue as it sits).

Deju vu?

FWIW, Skip, when I stay at the CY hotel on the upper east side, FM reception is marginal.

that could be building penetration of a nice steel building, which causes havoc to VHF signals.

If I were you, I'd be looking at alternative feeds unless you can get a window facing Empire with some kind of unique antenna and filters. (which is not what you want to hear, but....)

I said that earlier too.

My money is still on signal path attenuation being the prime culprit. The frequency change of 96.3 to 105.1 MHz only accounts for a wave length change of .25m, one can easily move the antenna and hear a difference if it was multi-path fading related. A reduction of 6dB of ERP can easily put that signal into the noise difficult signal path condition of an urban steel jungle. Often times it is hard to get signals into those urban canyons. Reflection off of the building can and do help more than hurt in these cases.

 

[ScottM]

Whatever, Scott.

My 5 years in NYC as a field engineer apparently don't count. Nor do the other 10 years working as a consultant on propagation and other issues.

Life's too short to argue about this kind of stuff.

I think you are just skipping over the most likely culprit, the reduction in the strength of the signal, to go for a less likely and easily testable issue. The station admits itself that the reduction on signal strength is going to result on about a 20% reduction of coverage. If it was a multi-path issue simply moving the radio to another table would have solved the problem.


So whatever back at you...


SIGH!

 

[EdFred]

Nerd Fight!!!!!!

 

[gismo]

I think you are just skipping over the most likely culprit, the reduction in the strength of the signal, to go for a less likely and easily testable issue. The station admits itself that the reduction on signal strength is going to result on about a 20% reduction of coverage. If it was a multi-path issue simply moving the radio to another table would have solved the problem.


So whatever back at you...


SIGH!

Seems to me that a reasonable directional antenna with a clear view of the sky would be the best solution regardless of whether this is a weak signal, multipath, or overloading issue (chances are it's a combination of at least two of those). Antenna amplifiers are really only useful for driving long feedlines and/or multiple splitters so I wouldn't bother with that especially considering that the Bose likely has a pretty sensitive front end in the first place. And while moving the antenna a few feet might indeed result in decent reception, chances are that A) this has already been tried and B) any improvement is likely all too temporary IME. If at all possible I'd go for a small FM yagi on (or under if external antennas aren't allowed) the roof.

 

[ScottM]

Seems to me that a reasonable directional antenna with a clear view of the sky would be the best solution regardless of whether this is a weak signal, multipath, or overloading issue (chances are it's a combination of at least two of those). Antenna amplifiers are really only useful for driving long feedlines and/or multiple splitters so I wouldn't bother with that especially considering that the Bose likely has a pretty sensitive front end in the first place. And while moving the antenna a few feet might indeed result in decent reception, chances are that A) this has already been tried and B) any improvement is likely all too temporary IME. If at all possible I'd go for a small FM yagi on (or under if external antennas aren't allowed) the roof.

Yep that is why I suggested that as the better solution in my first post in this thread.

But based on what Bill said my money is on the signal is just too darn weak. You could also try a signal booster. http://www.amazon.com/Metra-44-UA60-Signal-Amplifier-Bypass/dp/B0002IEDBW

Or better yet go to an external to the house direction antenna. If you still have a TV antenna these often also had the FM broadcast band covered in them and would be an excellent antenna.

I wonder if the Bose really has a decent front end. I really don't know. It has been my experience that most FM band radios for the broadcast band are pretty cheap and most rely on strong signals. There are some pretty good single chip FM receivers these days and the costs are in the dollar range.

 

[Capt. Geoffrey Thorpe]

Forget FM just click here:

Thanks for the link. Nice alternative to the Detroit classic music station
( wrcjfm.org - also available to listen to on line )

 

[Trapper John]

I wonder if the Bose really has a decent front end. I really don't know. It has been my experience that most FM band radios for the broadcast band are pretty cheap and most rely on strong signals. There are some pretty good single chip FM receivers these days and the costs are in the dollar range.

Bose seems to have a habit of not providing any technical specifications for their products. Makes me wonder why.


Trapper John

 

[Cap'n Jack]

Aside from the things mentioned by Bill & Scott, the reduced signal strength may be allowing other junk to be picked up on the new frequency. Cities are terrible for reception because of all the electronic noise from...well everything.

We found a junked FM radio today and put it in the lab with - we could only pick up a few stations (Lincoln, NE seems to have at least AM or FM 3 stations!!!!!). The rest of the FM band sounds like an old computer modem.

A good directional antenna (as the other guys mentioned) would reduce some of the noise...

 

[ScottM]

But then again, what do I know, apparently I need a lesson on inverse distance field.

It would seem that you do since you obviously really do not understand the affects of fading and bandwidth.

In our situation presented here: We see a very small change in wavelength, no change on the receiving or transmitting antenna locations but a huge change in transmitted power in a high noise environment, with difficult propagation characteristics. I am sure with all of your field experience you can tell me what the noise floor in that area is as I am sure you have it measured for your propagation studies to design coverage. That is always a first step in any study. But you want to go with multi-path fading as being the issue that needs resolution here. Interesting. That is not normally the first place to look.

But as I said, all Skip has to do is move the antenna a few feet. If it is a fading issue the signal will jump back up, if it does not then we know it is not.

RF design basics are first to ensure that there is a chance that a signal may be received. With a huge decrease in transmitted power, possible de-sense issues associated with being in a high noise area, not to mention the usual crappy receivers in COTS FM Broadcast equipment, the money will be on low signal strength at the antenna. But if you want to sell a line of bravo sierra on multi-path fading, go right ahead. I sure that you have an adequate supply of fan boys to cheer you on.

But I do note that you are now asking Skip to do EXACTLY what I asked him to do in my first post. hmmmmm.

Life's too short to argue about this kind of stuff.

I guess you found out you got an extension, congrats!!

BTW in a study that I did a long time ago, for frequencies that are higher than what we are talking about, the urban canyons and multi-path actually helped improve the chances of receiving a signal. But even though the coherence of the signal might cause some issues, the type of modulation being used in my study and RX line up, could tolerate the fades due to separate receivers working out of phase and then using a time base to reconstruct the signal. This is similar to using a diversity antenna scheme.

I am looking at several FM broadcast band all in one chips. These retail for under $4 and a couple I have seen are capable of using a single antenna diversity (NOT true diversity) scheme to minimize fading in a mobile environment. The cost to implement that is but a few cents so it would not surprise me to see that employed in many COTS radios. Without seeing the specifics from Bose we will not know for sure.

in closing....lighten up Francis!

 

[TangoWhiskey]

in closing....lighten up Francis!

That's THIS thread: http://www.pilotsofamerica.com/forum/showthread.php?t=32326

 

[ScottM]

**** off, Scott. I understand it every bit as well as you do, and you might realize that if you'd put your arrogance aside for a minute and respect the fact that other folks have knowledge and experience, too.

Moving a few feet won't fix the problem. Moving a few feet when hit with multiple reflections will move the null points through the baseband - all it takes is knocking out a portion of that L-R amplitude modulated subcarrier, but are unlikely to clear it entirely (esp with a wavelength on the order of 10 feet).

Yeah, consumer receiver front ends are ****. But most every one I've run across will handle a 6 dB change in a high signal area without effort.

Whatever Bill.

It is obvious that you are taking this discussion way too personally.

 

[ScottM]

Skip find an outside antenna or listen on the Internet. Sounds like you are now part of the almost 25% of people who have lost the signal from that station due to the power reduction.