October 5, 2016 at 3:52 pm #23620
Thanks for the sanity check, the maps look fairly similar. Considering the price I paid for use of the on-line plots, (nothing) I am pleased with the results. 🙂
Going to try it on KIEV-LP and KISN-LP (which are somewhat weaker) next.October 5, 2016 at 5:57 pm #23623
You can clearly see where the west hills stop the signal. It goes from orange to green with just a little strip of yellow (which I believe is the east side of the peak and the peak itself) and the green is the back (west) side of the ridge.October 5, 2016 at 7:07 pm #23624
To a broadcast engineer, the signals stop at the edge of the 60 dBu contour… to a dxer, that’s where the fun begins. 🙂October 7, 2016 at 1:46 pm #23654
Not exactly. At the edge of the 60 dBu contour, with respect to full service FM stations, is where the interference can begin. With LPFM stations, even the area inside the 60 dBu contour is not immune (nor is it with full service stations depending on major topographic obstacles). First case in point, try listening to Portland full service FM’s in the Terwilliger curves. Second case in point, half of PRP/KSFL’s primary reception area (60 dBu) is encompassed by Eugene’s KODZ’s 40 dBu contour. Aloha and Hillsboro are completely contained by the KODZ 40 dBu contour, resulting in lots of potential interference depending on topography as well as the receive antenna directional properties. In full service station compliance a proposed 60 dBu can never overlap a co channel’s 40 dBu. That’s why the 40 dBu contour is often called one of the ‘interfering’ contours. The others are the 54 dBu contour for first adjacent and 100 dBu for 2nd and 3rd adjacent. Those of course are for stations in Zone II. Zone I stations (back east and some of California) use different contour values due to the fact that there are no Class C’s, just A’s and B’s.
Longley Rice analysis is a great tool but it is a propagation model that looks at signal strength, height and terrain. It does not take into account co channel or adjacent channels in the area. To do that you have to do an interference study which is basically like doing a Longley Rice for both stations and then seeing who is stronger in the area being examined. The difference may not be very great in which case the receive antenna becomes the critical component in an effort to reject the undesired signal. In this case the possibility of both KFSL and KODZ being present at approximately 40 dBu is highly probable out in the Aloha/Hillsboro area.
Anyway, you can see from just examining the FCC contours on the above map that in many cases out in the Hillsboro and Aloha area, obtaining 20 dB difference between desired and undesired (kind of the ‘standard’ for interference free reception) is not guaranteed anywhere. The problem is the same for the north half of KSFL’s signal as a result of the Longview translator.
So although DX’ing fun may be greater outside a station’s primary signal (60 dBu) it isn’t that much of a mystery when you are still dealing with ground wave propagation. Skywave is more of a mystery but in this case it is too close to expect that has any measurable role in receiving PRP on the west side.
FCC guidelines for placing LPFM stations are quite clear. Paraphrasing the FCC, even though a proposed LPFM site may meet all distance requirements to co channel and adjacent channels, it may not be a workable solution. We saw that with Free Form Beaverton who moved off of 94.3 because of ZZR on Mt. Hood’s great line of sight into Portland, so they went to 98.3. Many many LPFM’s are located in part and sometimes almost entirely inside of a co channel’s 40 dBu contour. What I’m working on in Salem has this issue but the hills to the south of Salem block the co channel in Veneta. In the case of PRP, the Tualitan hills probably block a good portion of the Eugene signal. Those are some of the characteristics that a good siting engineer takes into consideration. Unfortunately, many proposals are not planned or chosen that way which is why so many LPFM’s have to move. The other reason they move is because the original proposals are placed on existing towers with absolutely no reasonable assurance from the tower owner that they would actually lease space to an LPFM.October 7, 2016 at 4:17 pm #23663
Does the FCC allow the use of alternate methods of contour plotting (such as L-R) in areas with difficult terrain or areas where the normal calculations (which ignore terrain features past 16 km from the transmitter) tell an incomplete story?October 7, 2016 at 4:28 pm #23665
In some cases they do. However, not as a substitute for FCC approved methods and calculations. Mostly you have to make a long winded showing of what you get the standard way and offer an alternate method as a comparison. Longley Rice is often used for showing there is or is not coverage where the FCC method says the opposite and can sometimes help get a waiver or support a non-interference claim. For example, a fill in translator can not provide coverage outside the FCC 60 dBu contour whether or not that contour is accurate.
Remember, Longley Rice doesn’t always show better coverage then the FCC method it can also and often does show worse coverage then the FCC method. It’s hard to see that when you’re looking at LPFM’s but when you are looking at a L/R for a full class C you often get pockets of no coverage well within the 60 dBu. It’s a great tool to have and not necessarily just for application work.October 9, 2016 at 9:16 pm #23761Chris_TaylorParticipant
Local artist Tim Ellis, who died earlier this year at age 60, had always been a fan of PRP. He had office and studio space at Days Music. Prior to his death, he had offered it to be used by PRP.October 9, 2016 at 11:15 pm #23763mwdxer1Participant
There is also another signal 45 miles from Portland at Longview WA. So far I have not caught 99.1 Portland out here on the Northern Oregon Coast. The lp stuff over the Coast Range is not easy.October 10, 2016 at 4:14 pm #23791Craig_AdamsParticipant
Kent Randles reports: KPQR-LP has turned in their license.October 11, 2016 at 9:51 am #23815
“The lp stuff over the Coast Range is not easy.”
I would think not… got your Körner antenna yet?October 11, 2016 at 12:50 pm #23823October 12, 2016 at 4:52 pm #23893
Here Brian B. (K6STI) models and has pictures of the largest version:October 12, 2016 at 9:28 pm #23904Alfredo_TParticipant
That Korner 19.3 is HUGE. The Korner 19.4 is even bigger!
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