Shared AM transmitter sites.

[xmtrland]

I know of a lot of diplexed AM sites (two AM stations using the same towers). Are there any sites that Triplex AM stations (three AM’s off the same towers) or more for that matter? Are there any sites with three 50KW stations sharing towers? What is the biggest shared AM site in the US.

Are there any communities like Vashon Island that are home to seven AM stations transmitters. Of the seven stations there are two shared sites on the Island with two 50KW each. Two single 50KW plants and a 5KW plant for a total count of 5 actual transmitter sites on the island.

If you have not seen them yet see them here http://vashonradio.com/towertour/

I’m just wondering if there is an operating AM site with more than two AM stations sharing the same towers.

 

[nmoore6676]

KIST-1340, KZBN-1290, and KBKO-1490 in Santa Barbara California and all on one of those flag pole antennas. There are likely a lot more as real estate prices along with NIMBY's are making AM transmitter sites very expensive to maintain.

Another interesting question would be how many AM's operate from wires strung on TV or FM towers?

 

[Doctor_Technical]

How about tri-, quad- or quint-plexed? Honolulu, HI has 12 AMs jammed into 3 towers. One tower carries 3 signals; one has 4 and the final one has 5!

 

[xmtrland]

How about three 50KW directional stations from the same set of towers.

I can see 2,3,4,5 or more non directional stations using one common tower but what about three or more 50KW directional stations using the same set of towers.

 

[OKCRadioGuy]

If they have the same pattern it might be pretty simple. If they don't I bet it would be quite a mess.

 

[fybush]

If they have the same pattern it might be pretty simple. If they don't I bet it would be quite a mess.

The technology is certainly there to do it - it's just a question of whether it's worth the costs involved. When diplexing or triplexing is done right, it's not cheap. There are only a handful of companies and consultants I'd trust to do it right.

I just recently visited a site near NYC that has 8 towers shared by two stations - 10 kW DA-2 on 1660 (2 towers day, 4 towers night), 5 kW days/13 kW nights DA-2 on 1380 (3 towers day, 4 towers night). It takes a lot of filtering to make everything play right, especially with a bunch of 50 kW stations all located less than a mile away.

 

[w9wi]

If they have the same pattern it might be pretty simple. If they don't I bet it would be quite a mess.

The proper inter-tower spacing and phasing is frequency-dependent. So I don't think it would be any easier if the stations had the same pattern. (in any case I would suggest the chances of more than one station in the same market having the same DA pattern is pretty close to zero as well!)

 

[LA_Guy]

There's a triplex in Boston

Two towers west of Boston are home for 650 (250 watts ND), 1060 (40 kW DA) and 1200 (10 kW ND).

Five towers going up in Boston will be used for 1200 (50 kW DA-N), 1330 (25 kW DA-2 I believe) and 1600 (20 kW DA)

 

[boiseengineer]

On a "quickie" (build it or loose it) diplex I know about has one tower feed point of 6 ohms +J 290. Sun comes out & it changes the CP. 3 dB bandwidth is about 2.5 KHz. The little BE transmitter has a permanent VSWR indication. I think if the consultant had been paid it could have been done right.

 

[fybush]

On a "quickie" (build it or loose it) diplex I know about has one tower feed point of 6 ohms +J 290. Sun comes out & it changes the CP. 3 dB bandwidth is about 2.5 KHz. The little BE transmitter has a permanent VSWR indication. I think if the consultant had been paid it could have been done right.

If this is the diplex I think it is, it probably doesn't matter - station #2 isn't even on the air, is it?

 

[radiotower40]

How far away on the dial do stations have to be to diplex? Could you have a station say at 1570 and 1600 on the same tower?

 

[LA_Guy]

It depends on the power levels involved. If both were fairly low power (1 kw or less) it might work. The problem is getting the isolation filters to work for stations that close in frequency. You'd probably have to use some kind of hybrid (lossy) combiner-and if you did that, half of each stations' power would be heating a resistor. I'm not even sure the FCC would allow it. I do know that in the case you stated, the FCC will not allow the 25 mV/m contours of stations separated by 30 kHz to overlap, so your scenario would be impossible from an allocations perspective.

The general rule of thumb is 100 kHz or more frequency spacing, and none of the stations can be harmonically related.

 

[dbdigital]

On a related question: what is the current FCC position on longwire or inverted L antennas? I know there's a station in Washington that is using one under an STA (on top of the station owner's house) and KYPA in Los Angeles has their "hammock" antenna located atop a downtown building which they still use.

And what is the FCC position on EH antennas? I read somewhere that KYET in Williams, Arizona might be using one.

I guess the point is that with land use becoming a problem for AM stations, particularly in urban areas, station owners need to get creative with solutions new and old.

db

 

[boiseengineer]

If this is the diplex I think it is, it probably doesn't matter - station #2 isn't even on the air, is it?

Not on anymore. Bank's suing for unpaid loans.
These were 460 KHz apart, but the ATU losses for the add-on frequency were so much they had to run 350 watts just to get the field equivalent of 250 watts (minimum efficiency).

 

[MW_FM_DT_DXer]

KYET's antenna is EH, being used under STA. http://fjallfoss.fcc.gov/cgi-bin/ws.exe/prod/cdbs/forms/prod/cdbsmenu.hts?context=25&appn=101228088&formid=910&fac_num=64357

 

[dbdigital]

KYET's antenna is EH, being used under STA. http://fjallfoss.fcc.gov/cgi-bin/ws.exe/prod/cdbs/forms/prod/cdbsmenu.hts?context=25&appn=101228088&formid=910&fac_num=64357

Thanks for the link. The application says that they're using a horizontal longwire (300' long x 20' above ground level) at 50 watts. Maybe that's how their able to use an EH with the FCC's blessing. Of course, the station has been dark for a while so I guess anything is an improvement.

db

 

[radionekkid]

No closer than about 10 percent about 100 kilocycles worst case was 45 kilocycles and then only at lower power levels. Wire antennas only granted on sta and remaining flat top is grandfatherd situation. A big six tower is going on in orlando 540 and 740 kilocycles 50kw each. from theoretical it not as difficult as it sounds but you have to be careful and the hardware is expensive, labor and time consuming. Cost rises to exponent of number of stations involved in most cases. I saw one that worked fine but filter would set the hindges on the enclosure on fire.

 

[CW]

If they have the same pattern it might be pretty simple. If they don't I bet it would be quite a mess.

The technology is certainly there to do it - it's just a question of whether it's worth the costs involved. When diplexing or triplexing is done right, it's not cheap. There are only a handful of companies and consultants I'd trust to do it right.

I just recently visited a site near NYC that has 8 towers shared by two stations - 10 kW DA-2 on 1660 (2 towers day, 4 towers night), 5 kW days/13 kW nights DA-2 on 1380 (3 towers day, 4 towers night). It takes a lot of filtering to make everything play right, especially with a bunch of 50 kW stations all located less than a mile away.

Scott,
an X BAND station DIRECTIONAL????EVEN DURING THE DAY??? I thought ALL XBand stations were omni and 10KW Day/1KW night....WHO runs 10KW at NIGHT on 1660?? or was that freq a typo???

 

[fybush]

Scott,
an X BAND station DIRECTIONAL????EVEN DURING THE DAY??? I thought ALL XBand stations were omni and 10KW Day/1KW night....WHO runs 10KW at NIGHT on 1660?? or was that freq a typo???

It's allowed now under certain specific circumstances. The station in question (WWRU Jersey City) isn't even the only such case - look at KDIA in California, for instance.

 

[LA_Guy]

If they have the same pattern it might be pretty simple. If they don't I bet it would be quite a mess.

The technology is certainly there to do it - it's just a question of whether it's worth the costs involved. When diplexing or triplexing is done right, it's not cheap. There are only a handful of companies and consultants I'd trust to do it right.

I just recently visited a site near NYC that has 8 towers shared by two stations - 10 kW DA-2 on 1660 (2 towers day, 4 towers night), 5 kW days/13 kW nights DA-2 on 1380 (3 towers day, 4 towers night). It takes a lot of filtering to make everything play right, especially with a bunch of 50 kW stations all located less than a mile away.

Scott,
an X BAND station DIRECTIONAL????EVEN DURING THE DAY??? I thought ALL XBand stations were omni and 10KW Day/1KW night....WHO runs 10KW at NIGHT on 1660?? or was that freq a typo???

DA's are allowed on the coasts, where the main lobe is pointed out to sea (and away from other co and adjacent channel stations), and the null is less than 10 kW days and 1 kW nights.