Far Off Interference, Band Plans, And Omni Antennas

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by K0DUC, Feb 1, 2021.

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  1. K0DUC

    K0DUC Ham Member QRZ Page

    Tonight I did a check in with both my local club's net on their repeater repeater (65 miles away) and a half an hour later with the Canadian club across the border's net. The Canadians were very friendly, welcomed me in, and said I was blasting them with clear audio from the long distance, even with the hills working against me rather than to my advantage. My reception of them was rather poor, and hearing them was a slight issue. All in all, my second net of the night was working well.

    However, as the net went on, and the more I talked, a problem began to occur. Some of my transmission was lost, and I quickly assumed my Alinco 85 watt transceiver was overheating, which is a known problem with the model. This still may very well be the case. However, I also noticed that on my later transmissions, I wasn't just getting the Hayfield, Manitoba's signal, but every time I transmitted later in the net Bismark, ND's repeater on the same frequency. I didn't hardly believe it, and thought it might be some other interference, but eventually out of the garbled interference I did hear Bismark. By all appearances, I was somehow triggering a repeater 145 miles away.

    I ask the experienced hams here, what happened? I cannot believe that even my decent setup (85 watt transceiver, G7-144 antenna) with my height in the hills could have done such a thing? Was the overheating Alinco doing something it should not have? Was I getting a rare phenomena to get the reach and effect? Why was I having clear communication with the local repeater at first, and then the far off interference later? What can I fix?

    I suppose this is a good lesson in the problems of omnidirectionals, insomuch that you will end up getting signals on frequencies you don't want, and a directional has value in not taking in signals from certain directions. I guess it shows the power of band plans, and how I am in a unique situation tonight to actually have problems despite good plans (albeit in different countries). And how neither repeater has a tone, making weak signal contact easier, but also meaning this kind of situation was possible in the first place.

    Any guidance on this is welcome, and thanks in advance.
     
  2. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Temperature inversion as the surface cooled by radiation, causing Surface Ducting.
     
    WB5ITT, WA9SVD and N1IPU like this.
  3. K7JEM

    K7JEM Ham Member QRZ Page

    I think you have it figured out. I am wondering why the two repeaters have the same PL, unless one (or both) are carrier squelch access.
     
  4. K0DUC

    K0DUC Ham Member QRZ Page

    Niether have a PL. In fact, looking through the repeater directories fro both North Dakota and Manitoba, this seems to be very common. Both are quite depopulated with large open areas without a bunch of repeaters. If some places suffer from lack of bandwith, here ain't the place. Ghost town most of the time.

    In ND, both Bismark and Grand Forks have repeaters at 146.940, neither have a PL tone. Suppose they think they are far enough away, with enough geography to make it function? In Manitoba, it is a very popular frequency for repeaters, Flin Flon, Hayfield (the one in question), Thompson, and Swan River. Only Swan River has a PL tone. Sheer distance is probably enough to keep problems from happening.

    Indeed, the two repeaters that were fighting over my rig's reception are 202 miles apart. In most cases, it should never be a problem, and is a unique situation.
     
  5. KM3F

    KM3F Ham Member QRZ Page

    PL are used to help prevent such occurrences.
    I have one repeater that does use a PL and another on the same pair that does not.
    As a user, it's not you responsibly for those repeaters not using PL access.
    My position which can be disputed, is to not worry about the one you don't use.
    But, if emergency traffic is heard, not to interfere with out of courtesy.
    Here in the northeast it's common to hear other repeaters on the same assignment pairs but different PL.
    The PL won't provide any separation if both repeaters are accessed at the same time.
    In another case, a pair is assigned to a repeater not 1/2 mile away is also assigned about 70 miles way but with different PL.
    Using the far repeater PL accesses that repeater but not the one local to me.
    Bottom line here is if the local repeater is accessed while I am using the far one, 2 things happen.
    1. The local repeater takes over the frequency due to it's strength and I cannot hear the far repeater which is to be expected.
    2. A local area triggers the repeater, then everyone listening hears me talking to some one else and wonders what's going on because now an heard on both repeaters at the same time and vice versa.
    Lucky me, the local owner and I are good friends and has offered to allow me to disable his repeater when I want to use the far one, but not found it ever necessary for as much operation as I do.
    Bottom line for you, in my opinion, is not to worry about something you have no control over especially in another country.
    Examples of other issues in on 75 m band, 3.965 is a French commercial digital station on 7 evenings a week generating interference. The French "Amateur" has no privilege's in that portion of the band we use up to 4.0 as it's commercial to them otherwise. There are several digital station in our 75 m band that cause a lot interference.
    Some of it you just have to live with, otherwise ignore it, and in other cases use judgement.
    .
    If you complain, you might be told in no uncertain terms to use a low gain low mounted antenna so you don't interfere with other repeaters. Well you take that as you may. Otherwise go the other way and use a high gain beam with a narrow pattern pointed to the repeater you want to access, and to add to it , lower your power if you don't need 85 watts to do the job. Your radio was not really meant to run high duty cycles like your indicating and will overheat.
    So there are things you can do to help but it's not 'all' on you back.
    Repeaters are largely meant for mobile access where your issue would not be a problem plus elevation and propagation enhancement effects and use of gain antennas, high power levels all contribute to the overall issues.
    Good luck.
     
    Last edited: Feb 1, 2021
    KA0HCP likes this.
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    As explained already, likely temperature inversion causing enhanced propagation.

    I don't know how likely this is in wintertime in your area, but it's quite common in some areas and can occur any old time, but most often in early evenings.

    145 miles on 2 meters isn't unusual. Repeaters should all use CTCSS to help avoid stations keying up more than one at a time, but of course if multiple repeaters on the same frequency (even using CTCSS) are in use at the same time, there will still be interference on the output frequency.

    Here in CA we have many repeaters installed on hilltops over 6000 feet high and even without inversion or ducting, stations from 150 miles away use them. The 222 MHz repeater up on Frazier Peak (8000+ feet elevation) is used by "mobiles" up in Sacramento, about 300 miles to the north (although the path is very clear and over a large, wide, long valley all the way).
     
  7. KE8OKM

    KE8OKM Ham Member QRZ Page


    I’m no expert but if you are on a hill with 85w 145 miles is pretty unremarkable. I have had. as well as other Hilltoppers/SOTA enthusiasts 130+ mile QSOs with a 5W HT and a Rollup Jpole.
     
  8. K0DUC

    K0DUC Ham Member QRZ Page

    It goes to the problems of the terrain and landscape of North Dakota. When you start plotting and looking at the LOS and elevations, and using programs like Radio Mobile Online, it makes sense. To the flatlands around me, I'm on a good position to shoot signals south, but eventually the geography of the state changes and by the time you get to Bismark the landscape and position of the repeater, it makes very good sense.

    All the big boi power of my Alinco, all that big gain from that G7, the theoretical 380 watt ERP, isn't going to do much unless the LOS is clean and clear enough. The wrong elevation over that same distance, being on the right peak/hilltop, makes every last bit of difference.

    Lastly, what about squelch? With a different setup, I could not break the PL tone squelch of the local repeater 65 miles away with as much as ~120 watts ERP. My testing concluded somewhere around 180 watts was needed for the PL tone to break the repeater open. BUT, as soon as I did, it was reports of extremely clear, powerful audio that completely submerged the noise floor.....

    Are the hilltoppers running their squelch open, or very low, to get those weak signals? Are the repeaters, especially those without PL tones, running higher squelch to kill errant signals? Not merely a question of ability to talk with someone over your radio, but the ability to even open up the other radio in the first place.
     
  9. KE8OKM

    KE8OKM Ham Member QRZ Page

    About squelch hill-topping. I typically set it for slightly above where it is breaking with local conditions. I can say that LOS is a pretty straight forward concept but have had some seemingly impossible QSOs behind higher mountain ridge(s) possibly due too knife edge and reflection propagation. Like mentioned in this thread a beam that is pointed at your repeaters of interest may be your best option. Also If you are able to borrow another radio or have an HT give those a try with your antenna setup. Good luck!
     
  10. KN4ZKT

    KN4ZKT Ham Member QRZ Page

    It seems you are discovering the fun of VHF propagation. What happened to you is most likely tropospheric ducting. The interesting thing about this, is conditions can improve in one direction from your QTH, but not others. I often see good enhancement early in the morning on 2m and up. Often the higher bands are much better, as they don't need a big duct to be enhanced.

    I've keyed up a repeater 120+ miles away with a HT and a rubber duck running just 5 watts (and no I was not on a hill or a mountain).

    Check out the following links.

    https://en.wikipedia.org/wiki/Tropospheric_propagation

    Tropo ducting forecast: https://www.dxinfocentre.com/tropo.html

    APRS map that will built to catch real time openings: http://aprs.mennolink.org/#

    If you want to work long ranges on 2m and up, SSB is where it is at, with a good yagi. You will be shocked what you can do with so little. Troposcatter is a lot of fun, and its mainly where I hang out on (VHF bands). Don't be confuse troposcatter with tropo ducting. Tropo ducting just enhances troposcatter. You can easily talk 250+ miles on 2m ssb without any ducting.

    Highly recommend reading this link: https://www.qsl.net/oz1rh/troposcatter99/troposcatter99.htm
     

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