FM reception in parking garage. Is it the result of a leaky cable?

[fordranger797]

Hello,

I parked my car is a rather large underground parking garage the other day, and couldn't help but notice that most of the FM band still could be heard from my car radio once I entered the garage. At first, I figured that these stations could be received because they are transmitting nearby (10 miles, as the crow flies) at 50 KW to 100 KW, possibly providing enough power to penetrate the concrete. After driving down into the very bottom of the garage (far below ground, with more concrete in the way), all of these stations could still be received.

Are these stations coming through clearly as a result of a leaky cable antenna? Or would the power levels be sufficient to penetrate a concrete parking structure such as this? AM was completely obliterated once I enter the garage, as can be expected.

 

[PTBoardOp94]

No. There is no scenario where a leaky cable causes you to pick up more of your intended signal. If that was the case, you would see posts on here talking about the best sources for buying the "best leaky cables".

A "leaky cable" causes the antenna and tuner input to be less efficient, and may allow reception of unintended signals that would normally be blocked by the cable shielding.

 

[charlestondxman]

Probably. I’ve been in parking garages you get almost nothing on the top floor and stations a hundred miles away on the 8th floor.

 

[Schroedingers Cat]

Usually, there is reflection off of some metallic object which explains this, or ricocheting between such objects.

 

[Ai4i]

In the early days of CATV, the systems were horribly leaky and many of them put a combination of local FMs plus MTV and some services including Galactic Radio and/or SupeRadio on the FM band, but that was then and this is now.
Today, the systems all use the FM band for three TV channels sometimes numbered 95, 96, and 97. They have to be much more shielded because channels 98 and 99 are in the aircraft navigation band and THAT would never be allowed.
Many years ago, 145.25 in the two-meter ham band was a very undesirable repeater output frequency because cable channel 18's video carrier was right there and it would be present throughout a leaky CATV company's service area.

 

[boombox4]

FM reflects off of mountains. There's no reason it won't reflect off of concrete as well.

 

[channel99]

It is not unusual to have "rebroadcast" systems in highway tunnels to provide AM and FM reception where there would otherwise be little or none. Sometimes they are used in buildings and garages. Deliberately leaky cable distributes the signal.


https://www.rfiwireless.com.au/repeaters-rebroadcast/rebroadcast.html

 

[Schroedingers Cat]

CKLW, and later WJR, as both had Ed Buterbaugh as their CE at the time, had a leaky cable system to receive their broadcasts in the Detroit Windsor Tunnel. Wonder if he had it in the Holland Tunnel for WABC.

 

[seattlesarchiebunker]

It really depends.

I was blessed for years to park and drive daily in Downtown Seattle. The class C’s on the Cascade foothills (about 15 miles away) started petering out by the second basement level of my parking deck. That being said, the stations on the hill right next to downtown 3 miles away came in (albeit scratchy) all the way down to the 5th basement level!

What I non-scientifically think determines reception in a situation like that is if the tower can “see” you (I know, VHF/FM is line of sight). What I mean is if you could climb up the tower in question and point out the roof of the garage in question. It’s quite possible the stations you received are simply in an advantageous place for downtown parking garage reception even though it’s several miles away.

 

[Ai4i]

Wonder if he had it in the Holland Tunnel for WABC.

A friend of mine in Fort Lauderdale invented and sold the rights to "tunnel radio". I wonder if that Butter bag guy was a dual citizen or had to jump through flaming hoops to work in both countries. Canada is just as protective as this country is.

 

[Schroedingers Cat]

As I recall, he lived in Monroe County, MI, and either had Funeral Services or was buried in Harrow, ON, near the CKLW towers. So he had close connections to both the USA and Canada. Since the Detroit Windsor Tunnel is in both countries, it may have complicated the licensing. Did this guy in FL ever work at CKLW? I know that there is someone who posts or posted here who was a DJ at CKLW who lived in Florida. He used a different name at CKLW, as did most DJs there.

 

[Ai4i]

Did this guy in FL ever work at CKLW?

I don't think so.
He DJ'd at WHOT in Youngstown, Ohio, possibly KQV in Pittsburgh, and definitely WQAM in Miami. His big claim to fame was licensing, building, and running LPTVs throughout Florida including then W33AA and WFUN-LPTV, then selling them for millions.
Ham callsign is (or was) W4FM.
He partnered with W4YU on Fort Lauderdale's tunnel radio project.

Jolly Rodger
Johnnie Andrews
John Paul Roberts (JPR)

 

[kevtronics]

FM VHF signals bounce off concrete. That's what causes problems with multipath in urban areas.

But there are some tunnel radio systems which can broadcast the same thing on all channels in order to relay traffic and emergency messages to motorists no matter which station they're tuned to.

 

[Schroedingers Cat]

W4FM sounds like somebody referring to WWWW 106.7 Detroit. Doesn't sound familiar though, any of those names. Howard Stern (not an endorsement) worked at WWWW. WWWW, now WLLZ, has almost always been a grandfathered superpower station at 61000 watts.

 

[Ai4i]

W4FM is or was his actual amateur radio call sign
Mine is my Radio-Discussions screen name:
Alpha India 4 India
Always Itching 4 It

 

[Schroedingers Cat]

I realize that it is or was his callsign. Some vanity calls attempt to recall legacy commercial call letters.

 

[DXBob]

I realize that it is or was his callsign. Some vanity calls attempt to recall legacy commercial call letters.

This is true! My father was a ham radio operator. One of his local ham buddies was WA9WLS...

Bob

 

[Schroedingers Cat]

There was a CE from Indiana who had the Callsign W9LSX, but that was before vanity callsigns. WLS was one of the stronger signals in his area. He signed some station QSLs.

 

[Ai4i]

Barry Goldater's son eventuall inherited his dad's legendary K7UGA Call sign.
Jean Shepherd of WOR was K2ORS

 

[Kelly A]

No. There is no scenario where a leaky cable causes you to pick up more of your intended signal. If that was the case, you would see posts on here talking about the best sources for buying the "best leaky cables".

A "leaky cable" causes the antenna and tuner input to be less efficient, and may allow reception of unintended signals that would normally be blocked by the cable shielding.

Leaky cable transmit antennas are exactly that, poorly shielded cables intended to radiate along most of their length. Ever been to Disneyland or Disney World? The music being played during the Main Street Electrical Parade is via a leaky cable that runs the length of the parade route. Receivers in the various parade cars pick up the music signals from the cable.

As sort-of mentioned in this thread; leaky cables are commonly used as transmit antennas in tunnels for re-transmitting signals from outside the tunnel. A broadband I.F. tuner and amplifier are utilized to receive the signals, then re-transmit it into the tunnel. The concrete and rebar act as a Faraday cage, isolating the tunnel signal from the outside primary signals.