Tuesday night I was listening to my Insignia portable HD radio and pulled in WHPT 102.5 FM. The time was around 9:30 p.m. I not only received the station, but picked up the HD signal as well. Even the HD 2 station came through. I had gotten excited thinking that another local station had added HD. I was even more surprised to see that the signal was coming all the way fromTampa.
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WHTP 102.5 - HD came through all the way to Cape Coral
- Thread starter muiscmike
- Start date
Nothing in the way since the signal jumps over cows and barns. The closest frequency is 102.9 and today's radios are selective enough to ignore that adjacent signal.muiscmike said:
Remember, since I-75 travels east from Venice before turning south again through Port Charlotte, the mileage markers from Tampa/Sa-ra-so-ta! to Ft. Myers is a wee exaggerated when measuring the distance with regard to the radio signals between the two markets.
Jeff in Sa-ra-so-ta!
There are a number of different ways in which an FM station can generate an HD signal. One of those ways is to use what's called "space combining" - a completely separate transmission system for the digital system. That's what WHPT is doing: the analog signal comes from the existing analog transmitter and out the main antenna at 1650 feet up the tower; the digital signal comes from a separate transmitter feeding a separate antenna 1354 feet up the tower.
(It's also possible to have the digital and analog transmitters feeding the same antenna through a combiner, or even to generate the digital and analog signals out of the same exciter in newer models of transmitter; that's not how WHPT does it, though. Using a separate transmission path means the digital transmission system can double as a backup analog transmission system if the main transmitter fails, and it's always good to have an aux.)
As for the raised HD power, that's the "-14 dB" part. The originally-authorized HD power level was "-20 dB", or really "-20 dBc", which is to say 20 dB below the power level of the analog carrier. So for a 100 kW FM signal, -20 dBc would be 1 kW. The FCC's power increase allows most stations to run -14 dBc and some to go all the way up to -10 dBc, which would be 10 kW of digital power on a 100 kW analog signal.
(It's also possible to have the digital and analog transmitters feeding the same antenna through a combiner, or even to generate the digital and analog signals out of the same exciter in newer models of transmitter; that's not how WHPT does it, though. Using a separate transmission path means the digital transmission system can double as a backup analog transmission system if the main transmitter fails, and it's always good to have an aux.)
As for the raised HD power, that's the "-14 dB" part. The originally-authorized HD power level was "-20 dB", or really "-20 dBc", which is to say 20 dB below the power level of the analog carrier. So for a 100 kW FM signal, -20 dBc would be 1 kW. The FCC's power increase allows most stations to run -14 dBc and some to go all the way up to -10 dBc, which would be 10 kW of digital power on a 100 kW analog signal.
When HD first came out, you were only allowed to run -20dbc or 1% of your FM power for HD. For a 100kw station like WHPT, that was 1kw. Then the FCC allowed FM stations to run -14dbc or 4% of your FM power for HD. For a 100kw station like WHPT thats 4kw which is what they are running now. You can run as much as 10% of your FM power or -10dbc or 10kw for a 100kw FM station if you do an interference study and get permission from the FCC. I dont see WHPT doing that as thier HD coverage is so good at -14db or 4kw.
Keep in mind that its much easier for lower power stations to do HD as they can run both FM and HD through the same transmitter, so Class B stations like in the Northeast where they run much lower power can use the same transmitter and antenna for HD. Stations on the Empire State Building only run about 7kw effective radiated power compared to the 100kw we run here. We cant do "common amplification" down here because of the higher power levels. WHPT has a transmitter power of 34kw. It would take several transmitters combined together to make that much power for FM+HD. That just is not econonomically feasible. Thus the use of a seperate transmitter and antenna for HD.
Keep in mind that its much easier for lower power stations to do HD as they can run both FM and HD through the same transmitter, so Class B stations like in the Northeast where they run much lower power can use the same transmitter and antenna for HD. Stations on the Empire State Building only run about 7kw effective radiated power compared to the 100kw we run here. We cant do "common amplification" down here because of the higher power levels. WHPT has a transmitter power of 34kw. It would take several transmitters combined together to make that much power for FM+HD. That just is not econonomically feasible. Thus the use of a seperate transmitter and antenna for HD.
Jeff
No, the ratio of the FM to HD will be the same, assuming the Empire stations are running -14dbc. If a station is running only -20dbc the HD coverage will be less, if they are running -10dbc the coverage will be greater.
Its just harder to achieve down here since we run so much more power. A Class "C" station like WHPT can run 100kw with up to a 2,000 foot tower. Class "B" stations, which is the maximum station in the northeast, is only allowed 50kw at 500 feet. If you go over 500 feet you must reduce power. Thats whay the stations on Empire only run 7kw or less. It takes a much bigger transmitter to achieve 100kw FM, or 4kw HD than it does to make 7kw FM. In fact since the Empire stations run so little power, they can run both the FM and HD through the same transmitter. We cant do that.
The WHPT tower is 1,749 feet above seal level, 1667 feet above ground. The tallest FM in the state and the tallest tower on the west coast of Florida. Thats the maximum height the FAA would allow.
No, the ratio of the FM to HD will be the same, assuming the Empire stations are running -14dbc. If a station is running only -20dbc the HD coverage will be less, if they are running -10dbc the coverage will be greater.
Its just harder to achieve down here since we run so much more power. A Class "C" station like WHPT can run 100kw with up to a 2,000 foot tower. Class "B" stations, which is the maximum station in the northeast, is only allowed 50kw at 500 feet. If you go over 500 feet you must reduce power. Thats whay the stations on Empire only run 7kw or less. It takes a much bigger transmitter to achieve 100kw FM, or 4kw HD than it does to make 7kw FM. In fact since the Empire stations run so little power, they can run both the FM and HD through the same transmitter. We cant do that.
The WHPT tower is 1,749 feet above seal level, 1667 feet above ground. The tallest FM in the state and the tallest tower on the west coast of Florida. Thats the maximum height the FAA would allow.
I have not found the coverage of digital anywhere near the coverage of the FM signal. In fact, I have found that even in a city grade environment, the HD is unstable at best, non-existent at worse.rfrus said:
Is that because the FM signal is interfering with the HD so that if the FM signal was not on air, the perceived reception would be better for the HD?
Does 91.7 play a part with downtown St. Pete reception with regard to the 10.7Mhz or would that be "normal" multipath associated with buildings in the way, or just distance, or a combination of all three?
Jeff in Sa-ra-so-ta!
Just my 2 cent$ worth, until one of the HD experts (i.e. rfrus or hdradioeng) respond.badjef said:
As far as the HD2 signals being more difficult to capture even in the city grade contour, I would imagine at least two things are in play here......... in the example of WHPT, the HD2 is 4,000 kw vs 100,000 kw for the HD1 signal of WHPT and the HD2 antenna is almost but not quite as high as the antenna for WHPT HD1. Also the HD1 signal has the analogue signal to fall back on, if going under a bridge or other obsticle; the HD2 signal is stictly digital and like digital TV, it's an all or nothing proposition.]
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I'm not sure I understand the question/comment about 91.7 in downtown St. Pete (antenna located at s.e. corner of Central Ave and 4th St. ........... but I will tell you this, ever since they signed on the air in the late 1980's I noticed that the reception of WUSF 89.7 has not been as good......... maybe it's just a coincidence with something else that may have happened around the same time.
drt,
never an engineer,
never even played an engineer on TV or radio!
GO RAYS!
drt said:
All broadcast FM stations have a 10.7mHz IF frequency protection range. WFTI 91.7 is a 10.7mHz IF frequency to WHPT 102.5. In the case of WFIT and WHPT, if the two respective antennas are not separated by the minimum distance [tower-to-tower] one frequency will essentially cancel out the other. To put this to the test, take two standard radio receivers, tune one to 91.7 and the other to 102.5. If the 91.7 signal is stronger possibly because your radio may be closer to the 91.7 tower, you will not be able to receive 102.5 on the other radio.
The same is true regarding WLLD 94.1 and WRBQ 104.7. Both frequencies are 10.7mHz IF frequencies in relation to the other. When 94.1 was first proposed to move from Lakeland into Tampa, the 10.7mHz IF protection was an issue with regard to WRBQ. The plan was to move WRBQ to 104.5 C which would have eliminated any potential IF issues while also enabling WRBQ to once again become a full class C FM. However, a proposal for a new station on 104.3 A in Inglis [Crystal River] was simultaneously before the FCC under consideration which was in conflict with any proposed WRBQ move to 104.5 C. The final FCC decision was that 104.3 A Inglis was approved making it impossible for WRBQ to change frequency. As a result, WKZM 105.5 Sarasota moved to 104.3 [to free 105.5 New Port Richey to upgrade to a class C1] and 94.1 moved its tower to an area Southeast of Tampa Bay. From this location 94.1 was able to still provide limited city grade service over Tampa Bay while also protecting WRBQ.
the HD2 is 4kw vs 100kw
Keep in mind that in HD radio, signal to noise (s/n) ratio is not as important. In AM or FM a weak signal will sound noisey. In HD the signal can be weak, but as long as the digital signal can be decoded, even if its weak, the audio will be pristeen. This is simpifying things a lot, but all you need to do in HD is tell the difference between a "1" and a "0".
Thats why both HD radio and HD TV use less power than analog.
Keep in mind that in HD radio, signal to noise (s/n) ratio is not as important. In AM or FM a weak signal will sound noisey. In HD the signal can be weak, but as long as the digital signal can be decoded, even if its weak, the audio will be pristeen. This is simpifying things a lot, but all you need to do in HD is tell the difference between a "1" and a "0".
Thats why both HD radio and HD TV use less power than analog.
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