FCC Commish: Reallocate Channels 5 and 6 To LPFMers

[rfry]

... 2 ohms RF ground loss (what type of ground plane would that be, R. Fry?)

That is the typical r-f loss in a ground system consisting of 120 evenly distributed, buried radials, each one having a free-space wavelength of 90 degrees.

... an antenna consisting of a center-fed full-wave dipole (two stacked half-wave elements) (similar to what KFBK Sacramento uses)...

A Franklin antenna such as used for both radiators in the KFBK 2-tower directional array is not the same as a center-fed dipole, because the currents in the two halves of a 180-degree Franklin are in phase, and they are 180 degrees out of phase in a center-fed dipole.

The RMS of the daytime pattern of KFBK is about 3,546 mV/m at 1 km. So if you use that value with the FCC curves as in my previous post, you can estimate the omnidirectional fields yourself for about any combination of frequency and conductivity you wish.

If you want to consider practical/economic issues, remember that a "KFBK Franklin" becomes very tall for lower frequencies -- over 1,800 feet at 0.54 MHz.

How does a 180° radiator over 120 evenly-spaced half-wave buried ground radials compare/contrast with two stacked 180° elements (total length 360°), center-fed, without a ground radial system?

Despite what is given on some websites, it is unlikely that KFBK's Franklins could operate as efficiently as shown in the FCC database if they had no r-f ground. The two halves of the Franklin are just two monopoles in a single, co-linear array, and monopoles need to work against a good, low-resistance r-f ground to produce their rated gain.

But anyway, the 180-degree system you defined has an IDF of 2,700 mV/m at 1 km for 50 kW. KFBK's daytime RMS IDF is 3,546 mV/m at 1 km for for 50 kW.

I'll pass on your other questions, but maybe someone else will respond.

RF

 

[pianoplayer88key]

Interesting.... So I ran the calculations, and basically figured that even with 500kW on 540kHz and a ground conductivity of 3mS/m (I looked at the FCC conductivity map for Alaska and there were patches of 2's and 4's so I took 3 as an average), it wouldn't be enough to cover the entire state of Alaska. For example, assuming a IDF of 2697.008mV/m @ 1km, I come up with a distance of 250km, or 155mi, for the 0.27mV/m contour, which I believe would be a moderately weak signal in a rural environment. Considering that a station that would cover the entire of Alaska would need to have a coverage radius of upwards of 600-800 miles or so, and also I couldn't get the calculator to accept 1MW, 2.5MW or 5MW power levels that I tried... I'm thinking it'd take a whole lotta power to cover the entire state if mediumwave was used.

Anyone know if there's a way to apply the FCC data/curves for other frequencies, like longwave? I wonder if 1MW on 153kHz into a half-wave antenna over 120 quarter-wave radials might be enough to cover Alaska?

Also I got a bit of an anti-climatic surprise when I figured how well 500kW over 540kHz would go over seawater. I was thinking that groundwave signals might go thousands of miles over the ocean, considering I know of someone in the interior of the USA who has used 4-foot diameter loop antennas to pull in Chicago AM stations in the daytime from near Lubbock, TX, or so. However, it turns out that the field at 963 miles is about 85µV/m. That seems to me like it would be a very weak signal, and I doubt a Tecsun PL-380 (I own one, but am thinking it may be defective) or PL-310 (I believe R(ich?) Fry owns one) would have any chance of getting any recognizable carrier at that low level without help from an external antenna.


So KFBK's IDF is 3546mV/m @ 1 km. It appears that the ground conductivity between me and them averages about 10mS/m or so. I'm about 491.25 miles (or 790.6 km) from their transmitter, at a heading of about 330° or so. Using the graphs and the conversion factor as a guide, I find that KFBK's groundwave field strength where I am is approximately... well... off the chart.
However, on some winter days, I am able to hear a somewhat usable signal from KFBK at noon. What's going on? Daytime skip? Exceptional groundwave for the high frequency being used?

Another anomaly I've noticed. I understand that assuming all other factors are the same, a station on a higher frequency will drop off quicker than a station on a lower frequency. As for the IDFs for the two stations I'm comparing, 640 KFI's IDF at 1km is 374.98mV/m @ 1km (WOW... KFBK appears on paper to be MUCH more efficient even considering the much higher frequency!), and 1070 KNX's IDF at 1km is 400.73mV/m @ 1km. Any idea why KNX seems to be more efficient than KFI? And, now for the quirk I've noticed... I'm 111.03mi (hdg 313.5°) from KNX, and 98.86mi (hdg 321.7°) from KFI, yet KNX usually comes in at least a few dB stronger where I am. What gives? Is it possible that KNX, being west of KFI, is coming across more of a saltwater path (due to the curve in the coastline), whereas KFI is over more of a land path?

 

[w9wi]

However, on some winter days, I am able to hear a somewhat usable signal from KFBK at noon. What's going on? Daytime skip? Exceptional groundwave for the high frequency being used?

Yep: daytime skip.

The ionospheric layers that allow for propagation of distant radio signals don't just snap on at sunrise & snap off at sunset. They gradually fade in and out. (for this among other reasons, sunrise and sunset can be very productive times for DXing!) They also don't fade in/out at the same rate every day.

Since sunrise is later and sunset earlier in winter, the layers don't have as much "downtime" -- and on good days they may not fade out at all.

BTW, if you've noticed an AM station listed with a different power during "critical hours", this is why -- to protect the dominant station on the channel from interference during that period when the sun is up but there's still "skip" propagation happening.

 

[rfry]

RE: IDF of KFI vs KNX vs KFBK

For non-D AM stations the FCC lists the IDF at 1 km for an applied power of 1 kW, regardless of their licensed power.

Comparing the daytime 1 km, RMS IDFs of these stations at their licensed 50 kW applied power:

KFI = 2,651 mV/m
KNX = 2,833 mV/m
KFBK = 3,546 mV/m

The carrier frequency has nothing to do with the IDF of an AM broadcast station, as the 1 km IDF is the field intensity at 1 km over a perfect ground plane -- which has zero groundwave propagation loss for all frequencies.

The reason that KNX has a higher IDF than KFI is that the KNX radiator is longer (higher) in terms of wavelengths at KNX's frequency.

I'm 111.03mi (hdg 313.5°) from KNX, and 98.86mi (hdg 321.7°) from KFI, yet KNX usually comes in at least a few dB stronger where I am. What gives?

You might investigate if this is to be expected using the 50kW IDFs for KFI and KNX with the appropriate FCC curves for the conductivity and path length to your receive site.

RF

 

[Carmine5]

This isn't going to happen. Chapter 5 of the NBP clearly states that it is the FCC's goal to make the lower VHF band usable for DTV--not give it to radio.

There are many areas of the country in which TV stations on those two channels cannot relocate. And now that the broadcast television industry is under attack by the FCC, expect TV broadcasters to fight vigorously to retain ch. 5&6.

No, just because one commissioner expresses some interest in the idea doesn't mean it will ever become a reality.

c5

 

[LibertyNT]

What TV Station In their Right Mind Would want VHF Low? its useless for DTV.
And I seriously doubt those stations have nowhere else to go. Ch7 - Ch68 I guarantee you there's a place for them.
And yes I know 68 is out of core. I forget where core ends.

 

[w9wi]

What TV Station In their Right Mind Would want VHF Low? its useless for DTV.
And I seriously doubt those stations have nowhere else to go. Ch7 - Ch68 I guarantee you there's a place for them.
And yes I know 68 is out of core. I forget where core ends.

51 is the highest in-core channel.

WPVI Philadelphia is probably the biggest station on channels 5 & 6. And no, I don't see a place for them above channel 6. Every channel 7-51 has at least one other station within the necessary separation distance -- often as many as three. WPVI's pre-transition DTV channel was 64, they can't go back there.

 

[pianoplayer88key]

RE: IDF of KFI vs KNX vs KFBK

For non-D AM stations the FCC lists the IDF at 1 km for an applied power of 1 kW, regardless of their licensed power.

Comparing the daytime 1 km, RMS IDFs of these stations at their licensed 50 kW applied power:

KFI = 2,651 mV/m
KNX = 2,833 mV/m
KFBK = 3,546 mV/m

The carrier frequency has nothing to do with the IDF of an AM broadcast station, as the 1 km IDF is the field intensity at 1 km over a perfect ground plane -- which has zero groundwave propagation loss for all frequencies.

The reason that KNX has a higher IDF than KFI is that the KNX radiator is longer (higher) in terms of wavelengths at KNX's frequency.

I'm 111.03mi (hdg 313.5°) from KNX, and 98.86mi (hdg 321.7°) from KFI, yet KNX usually comes in at least a few dB stronger where I am. What gives?

You might investigate if this is to be expected using the 50kW IDFs for KFI and KNX with the appropriate FCC curves for the conductivity and path length to your receive site.

RF

Well... I haven't looked at the curve data, but I did break out the large format FCC conductivity map, and drew paths (in GIMP) from my site to KNX and KFI's site, and they're in the pic at the link below...

http://picasaweb.google.com/PianoPl...key=Gv1sRgCIer0efojpPg8AE#5484707348416706674

It appears that my suspicions are confirmed... KFI's path is pretty much entirely over land, whereas about half or so of KNX's path is over water.

Speaking of that conductivity map... anyone have any suggestions for how to cleanly piece it together digitally (I use the GIMP as my main photo editor)? It doesn't help that some sections seem to be slightly rotated, some edges are fuzzy and aren't exactly pixel-straight.

Also... how would I use the FCC Figure 8 calculator to figure out the IDF for a transmitter that uses the type of antenna that KFBK uses?

And.... if I was going to figure out the field strength, using the curves, over a path that has different conductivities over part of the path, how would I do that? I assume the first step would be to calculate the field from the transmitter site to where the conductivity first changes, then what's next after that? Also how is average skywave field strength calculated? I don't think it'd be true IDF, due to the fact that I believe the ionosphere does absorb signals some even on a "good" day, and due to the typical angle that the signal goes up, then refracts back, and the fact that the ionosphere isn't a mirror-like reflector at a constant height.

Also for the field strengths specified in the FCC database for DA AM stations... is that the field if the station was transmitting non-directional at the licensed power, or the highest field in the largest lobe of the directional pattern?

Also, how would you calculate a particular stations ERP (and if I understand correctly, that would be the transmitter power they'd need to use if they were non-directional in order to have the same field strength at a particular heading and distance), in a certain direction, if you know the pattern data, for example?

 

[rfry]

Also... how would I use the FCC Figure 8 calculator to figure out the IDF for a transmitter that uses the type of antenna that KFBK uses?

It won't do that, but the IDF of an AM station is shown on AM Query (whatever form of antenna it uses).

And.... if I was going to figure out the field strength, using the curves, over a path that has different conductivities over part of the path, how would I do that?

The FCC uses the "equivalent distance method" (research on the FCC website). But in your situation you could just refer to http://www.v-soft.com/ZipSignal/default.htm, which uses this method to calculate the field at the end of a path with different conductivities over its length. It also incorporates the directional pattern/ERP of AM stations in the calculation.

For a receiving location near Spring Valley, CA, the V-Soft site shows a groundwave field of 6.76 mV/m from KFI and 5.48 mV/m from KNX.

RF

 

[rfry]

RE: AM Frequency vs ERP vs "Coverage"

Here is a comparison of the field produced in Merced, CA, 120 miles from KFBK (1530 kHz) with the field produced in Argenta, IL, 120 miles from WLS (890 kHz):

Bearing, ERP, IDF Conductivity Field at Endpoint
deg. T kW* @ 1 km mS/m mV/m

KFBK 153 236.6 4707 15 0.45
WLS 205 83.3 2793 15 1.47

*relative to a 90-deg monopole using 120 buried radials each 1/4-wave long

The daytime groundwave field from WLS is about 3.3 X greater than the field from KFBK over a 120-mile, 15 mS/m path, despite the higher ERP from KFBK.

The 0.45 mV/m daytime groundwave field from WLS over a 15 mS/m path is 188 miles away, which is about a 57 % greater distance than the 0.45 mV/m field is from KFBK -- even though the IDF of WLS at 1 km is only about 59% that of KFBK.

This shows the value of the lower frequencies for daytime groundwave coverage in the AM broadcast band.

RF

 

[pianoplayer88key]

For zip code 91941, the place closest to my location, KFI is 6.69mV/m and KNX is 5.51mV/m... yet KNX is noticeably stronger - indicates 51dBu on my Tecsun PL-380 in a particular spot in the house, vs. KFI's 44dBu at the same spot.
Problem with that V-Soft Zip Signal site, though... is that many signals I have received in the daytime at my location are not listed on that site, including... 530 WNHV296, 560 KBLU, 590 KTIE (night is listed but not day), 610 KAVL, 680 KNBR, 700 KALL, 720 KDWN, 730 XEEBC, 790 XESU (under KABC with a good antenna), 810 KGO, 820 XEVMS(?), 840 KXNT, 890 KPB792 (may not be on the air now though, i'm not sure), 920 KPSI or X-whatever Ensenada, 960 KIXW, 970 KNWZ, 990 KTMS & XECL, 1050 XED, 1150 KTLK (maybe, but KCBQ's strong signal was elevating my noise floor to about 41-43dBu on the PL-380 making KTLK all but impossible to ID), 1180 KERN, 1190 KXMX, 1230 KXO, 1290 KZSB & KKDD, 1300 KROP & KAZN, 1340 KCLU, 1350 KTDD, 1370 KWRM, 1430 KWST, 1440 KDIF (maybe, either that or 1410 KCAL), 1490 KIST or KGBA (or both), 1510 KSPA, 1530 KFBK, 1540 KMPC, 1580 KMIK, and 1670 KHPY. Is there a way to calculate those stations?
Also, several local Mexicans are unlisted or are listed incorrectly, like 620 XESS (unlisted), 1030 XESDD (unlisted), 1390 XEKT (listed as on 1380 also on FCC's site, radio-locator shows it on 1380 with incorrect power) 1700 XEPE (1600 XEKTT comes up but XEPE is XEKTT's replacement, FCC site also shows it incorrectly, radio-locator is correct though). Also several Mexican stations have several listings for the same station, sometimes with a slightly different transmitter site, different power, etc. I've heard some of the local ones give their transmitter power in their TOH IDs, and considering that I know enough Spanish to be able to pick that (and a few other things) out, I usually prefer to listen to their IDs to find their transmitter power if I doubt what the FCC or Radio-Locator says.
Also, is there a way to figure out the field strength and other data of a station that no longer uses the facilities they used at the time I logged them, or are no longer on the air, including 660 KGDP Orcutt, CA (now KWVE Oildale, CA), 670 KBOI Boise, ID (changed directional pattern), 1610 WNUB568 (if I remember call correctly) Chula Vista, CA (off the air), just to name a few?


Also... basically... how do things like frequency, ground conductivity, etc, change the coverage of a station? For example...
If a station's transmitter power doubles (all other factors, including the antenna's electrical length, being the same, as in the other examples in this section of the post), how much greater is the field at a particular location, and how much farther is the same field strength? OR, increase the transmitter power 10 times.... OR... what increase in power would it take to either double the distance to the same field, or double the field at the same location, or increase the field 10x at the same location?
If you double the ground conductivity, how much farther does a particular field strength go, or how much higher is the field at the particular location? Or... same question as above about what increase in power, but in this case what increase in ground conductivity would it take to.... (see above).
Also, same drill with frequency... If you half the frequency, how does it change the coverage, for example?

And how do you figure out the ERP of a station in a particular direction? I used to have a program several years ago that would show it (that I got for free, but I believe had a paid version so I didn't have all the features), but can't remember what it was now, and can't find it anyway.

So if I can sometimes get noontime reception of KFBK from about 500 miles away... I wonder how far WLS would go? Or better yet... a signal on 540kHz with the IDF efficiency of KFBK's antenna, 50kW and a ground conductivity of 30mS/m, or 5,000mS/m?

 

[rfry]

Problem with that V-Soft Zip Signal site, though... is that many signals I have received in the daytime at my location are not listed on that site...

Maybe you should address your question to V-Soft...?

Also... basically... how do things like frequency, ground conductivity, etc, change the coverage of a station? For example...If a station's transmitter power doubles (all other factors, including the antenna's electrical length, being the same, as in the other examples in this section of the post), how much greater is the field at a particular location ...

That answer is quick -- the groundwave field at any location will change by the square root of the change in radiated power. Twice the power = 1.414 x the original field, 1/2 the power = 0.707 x the original field, etc.

... and how much farther is the same field strength? OR, increase the transmitter power 10 times.... OR... what increase in power would it take to either double the distance to the same field, or double the field at the same location, or increase the field 10x at the same location? (etc etc)

These and your remaining questions can be answered if you use the FCC groundwave propagation curves. It will take some time and effort.

RF

 

[Carmine5]

What TV Station In their Right Mind Would want VHF Low? its useless for DTV.
And I seriously doubt those stations have nowhere else to go. Ch7 - Ch68 I guarantee you there's a place for them.
And yes I know 68 is out of core. I forget where core ends.

The FCC recently issued a VHF allotment on channel 5 to Seaford, Delaware. We'll see who bids on it when it comes up for auction. But the fact that the Commish would even do this is a strong indicator that the lower-VHF band will remain for television.

c5

 

[fybush]

Problem with that V-Soft Zip Signal site, though... is that many signals I have received in the daytime at my location are not listed on that site.

Some of the stations you mention don't appear because their calculated signal strength is lower than the minimum that V-Soft sets for its free display. Remember that the Zip-Signal site is just a freebie teaser that Doug puts out there as an enticement to check out the other products he offers, which are not cheap but are worth every penny, IMHO.

TIS stations like WNHV296 don't appear in the FCC CDBS database that V-Soft uses, since they're not licensed as broadcast stations.

And Mexican listings in CDBS (like Canadians) reflect only what US stations are required to protect by international treaty, not necessarily what's actually on the air in Mexico. I'm not sure that the international status of XESS, for instance, has ever been resolved by the FCC and Mexico's COFETEL (or by the diplomats who'd negotiate such matters.)

 

[Carmine5]

What TV Station In their Right Mind Would want VHF Low? its useless for DTV.
And I seriously doubt those stations have nowhere else to go. Ch7 - Ch68 I guarantee you there's a place for them.
And yes I know 68 is out of core. I forget where core ends.

The FCC recently issued a VHF allotment on channel 5 to Seaford, Delaware. We'll see who bids on it when it comes up for auction. But the fact that the Commish would even do this is a strong indicator that the lower-VHF band will remain for television.

c5

Well, here's a tantalizing bit of info: according to someone on an LPTV board, the FCC is holding all applications for channels 5 and 6 until the proposed rule making to expand the FM band is decided upon. This is according to an email from Hossein Hashemzadeh who is an Associate Division Chief in the FCC's Video Division.

So only time will tell as to where these channels will ultimately end up.

c5

 

[pianoplayer88key]

What TV Station In their Right Mind Would want VHF Low? its useless for DTV.
And I seriously doubt those stations have nowhere else to go. Ch7 - Ch68 I guarantee you there's a place for them.
And yes I know 68 is out of core. I forget where core ends.

The FCC recently issued a VHF allotment on channel 5 to Seaford, Delaware. We'll see who bids on it when it comes up for auction. But the fact that the Commish would even do this is a strong indicator that the lower-VHF band will remain for television.

c5

Well, here's a tantalizing bit of info: according to someone on an LPTV board, the FCC is holding all applications for channels 5 and 6 until the proposed rule making to expand the FM band is decided upon. This is according to an email from Hossein Hashemzadeh who is an Associate Division Chief in the FCC's Video Division.

So only time will tell as to where these channels will ultimately end up.

c5

So if the FM band is expanded down to....say... 76MHz (lower boundary of TV ch. 5)... I'm wondering if it will mostly be an extension of the non-comm part of the FM band (currently 88-92MHz, if so, would be 76-92MHz), or will be more for commercial stations?
Personally, I think it should mostly be for LPFM stations, and for part 15 with expanded field strength limits compared to the current FM rules. I might also consider allowing full power and/or commercial stations there, but would not allow IBOC, and would limit how many could be in a particular market. For example, in a market like L.A. or New York, the full power stations in the expanded FM band might be about as dense as the signals (not including translators/boosters) from 92-108MHz in a given town in the western USA (west Texas, northern Nevada, etc.) with a population of less than 15,000, that is not within 100 miles of a town with a population greater than 75,000.
Also, considering my idea that 76-88MHz (well, actually let's make it up to 92MHz since that portion of FM is also non-comm) should primarily be for LPFMs (with a few other high-power stations as well, with one other category I'll get to shortly)... I'd like to see the field strength limit for part 15 expanded in that section of the band (76-92MHz). In my opinion, just having 250µV/m at 3 meters just isn't enough. I was looking through the FCC part 15 rules to get some other ideas... and I see that in 15.245(b), a couple bands (around 10GHz and 24GHz) are allowed 2,500mV/m @ 3 meters for certain uses. I think the same limit should be adopted for 76-92MHz.
As for one other use... I'd like to see some of the smaller coverage AM stations moved to this expanded FM band, to somewhat help clean up the AM band. Then, AM should be mostly reserved for stations that are designed to have a wide coverage area beyond what any full-power FMs can cover, especially groundwave. I would also continue to allow part 15 on AM, and would also allow LPAM, mostly at 1200kHz and above. (I might also consider LPAM allocations below that, especially in areas where there's no room above 1200khz (even if you ignore 2nd-adjacents), or the ground conductivity is very poor (equal to or less than 4 mS/m). The power limit for LPAM should probably be between 10 and 50 watts, with an antenna no taller than 1/8th or 1/10th wavelength... or it should be short enough to not require an aircraft beacon in most places (I believe that's 200 feet but I'm not sure). I would also discourage the use of directional antennas, but would permit it in some cases. As for part 15... I'm thinking a limit of 1 watt input into the antenna terminal, with a 25 meter radiating antenna element (not including the shielded transmission line and ground lead) should be sufficient.

Now... I wonder what will happen to TV channels 2-4? I know there's a 72-76MHz gap between ch. 4 and 5, so it would be difficult, if not impossible, to smoothly expand the FM band all the way down through TV ch. 2.

 

[w9wi]

The FCC recently issued a VHF allotment on channel 5 to Seaford, Delaware. We'll see who bids on it when it comes up for auction. But the fact that the Commish would even do this is a strong indicator that the lower-VHF band will remain for television.

While I don't see the reallocation of channels 5 and 6 as a foregone conclusion (or even necessarily likely), I also don't see the allotment of channel 5 to Seaford as showing support for low-VHF DTV.

The FCC is obligated by law to allot at least one VHF channel to every state. 48 states already had at least one; New Jersey and Delaware were the exceptions. The law specifically requires *VHF* allotments. No high-band VHF channel is available in either state. (high-band stations exist on every channel 7-13 in NYC, eastern Pennsylvania, or Philadelphia)

Channel 6 was not available for this allotment because of WPVI. Channels 2 and 3 were not available because the licensee of two Western stations has filed to take advantage of aforementioned law and move their channel 2 and 3 stations from Wyoming and Nevada to New Jersey and Delaware. The FCC has rejected their applications but their appeals are still active. If the courts overturn the FCC decision, channels 2 and 3 will be required for these two stations. Channel 4 is not available because the FCC has assigned it to Atlantic City, New Jersey. (for the same reason it assigned 5 to Seaford)

 

[DJboutit3]

I would like to see 5 & 6 used for both unlicensed broadcasting & LPFM
150w 100ft antenna for unlicensed broadcasting this would stop pirates on the commerical band & FCC could use the money they spent fight pirates for other things
250w 150ft antenna for LPFM

 

[Carmine5]

One interesting suggestion that has been proposed by the broadcast attorneys at FHH is that of allowing all channel 6 license holders to exchange their television license for a full power commercial FM license on 87.7.

This would provide both a fair compensation and inducement for those existing license holders as well as free up the remaining 5.2 MHz for FM radio. If it hasn't already been discussed with the FCC, I'm sure the idea will be put forward when the matter of ch.5 & 6 reallocation is solicited for comments. c5

 

[w9wi]

One interesting suggestion that has been proposed by the broadcast attorneys at FHH is that of allowing all channel 6 license holders to exchange their television license for a full power commercial FM license on 87.7.

This would provide both a fair compensation and inducement for those existing license holders as well as free up the remaining 5.2 MHz for FM radio. If it hasn't already been discussed with the FCC, I'm sure the idea will be put forward when the matter of ch.5 & 6 reallocation is solicited for comments. c5

I don't think most broadcasters would consider swapping their TV license for a FM license.