DX reciprocity?

Discussion in 'General Technical Questions and Answers' started by Pushraft, Nov 20, 2008.

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  1. Pushraft

    Pushraft Banned

    I didn't say the same results could be achieved. I said tilting an antenna changes the elevation pattern. I dont know why he uses that setup but am hoping he will answer that question himself here. First of all, what band is it for? It may be related to 1/2 WL height above ground which I keep seeing popping up for some reason. I would assume that is a good antenna height to get a reasonably low radiation angle is that correct? Can someone answer why WWV in Colorado uses exactly this 1/2 WL antenna height for each frequency antenna they use? What is so "magical" (beneficial) about 1/2 WL antenna height?

    It just so happens that my 20m attic dipole is about 33 ft above ground and that is exactly 1/2 WL. I dont know how much difference that really makes but I am hearing a fair amount of people even on the lower 80m bands at night. W5KU for example in TX. Maybe that is the only antenna I need for Rx.
     
  2. KJ4AUR

    KJ4AUR Ham Member QRZ Page

    Removed May 07, 2009
     
    Last edited: May 7, 2009
  3. Pushraft

    Pushraft Banned

    best ground hop surface?

    Since WB2WIK brought up hops and trying to minimize them with a low takeoff angle, what is the best surface as far as ground "hops"? That is, what type of bounce on the Earth is most beneficial to DX with the least amount of attenuation? For example, does it hop better when it hits salt water, fresh water, dry land, flat land, hilly land... Also, which is the worst to try to bounce off of?

    I am somewhat amazed that it has enough "gusto" to even bounce the first time after coming down from the atmosphere.

    I sure am learning a lot in this new hobby of mine. Sure beats CB and FRS although those are useful for other things such as testing and local license free communication as well as much smaller antennas.
     
  4. KJ4AUR

    KJ4AUR Ham Member QRZ Page

    Removed May 07, 2009
     
    Last edited: May 7, 2009
  5. G3TXQ

    G3TXQ Ham Member QRZ Page

    DX (ARRL Antenna Book) = Long distance Communications

    Why did you wrongly assume that tipping improved the signal at low elevation angles. What I said was "At all elevation angles from 5 degrees thru 20 degrees the biggest difference was 2dB". In fact, at some low angles it is better upright; at other low angles it is better tilted.

    Steve
     
  6. W0IS

    W0IS Ham Member QRZ Page

    In general, the signal does not "hop" off the surface of the earth at some distant point (despite occasional pictures in books showing the signal hitting the earth at one angle, and being reflected at the same angle).

    The signal is reflected off (by being refracted through) the ionosphere. In the case of multiple "hops", the signal is not reflected by the surface of the earth, although if it comes close to the earth, it might appear to be a reflection with angles of incidence and reflection of 90 degrees.

    And yes, I'm sure you can come up with some exception where the signal is "reflected" by the earth's surface. But that's generally not what happens.
     
  7. Pushraft

    Pushraft Banned

    Will do thanks. I think that is 9PM my time (Eastern time). The guys I heard down on 80m were on 3.835 and 3.818.9 Mhz both USB. I didn't think a 20m attic dipole would pull those in but it did. I also heard WWV on 5 and 2.5 Mhz at night fairly well (fading of course). Sometimes I can hear the "ticks" very clearly but that usually doesn't last long. Remember I am in FL about 1500 miles away from WWV in Colorado.

    Pretty impressive for 33 ft of speaker wire surround by wood (in attic) with an alligator clip on the center pin (couldn't find my soldering iron).

    Well time to go buy some Samuel Adams so I can test out my "beverage" Rx antenna tonight. Or is that when they climb up on a 100 ft tower with a wrench in one hand and a cold one in the other hand? (not recommended).
     
  8. G3TXQ

    G3TXQ Ham Member QRZ Page

    Push, I'm still waiting for the URL of a "tilt adjuster" for an HF antenna. I'm genuinely interested to see what it looks like. W8JI will probably want one, too; then he can drop his antennas some ;)

    Why not do some of the work for yourself? By now you should have enough knowledge to work out at what frequency 180ft would be a half-wavelength. Then look back through W8Ji's posts and see if that's the band he was talking about.

    Steve
     
  9. W0IS

    W0IS Ham Member QRZ Page

    It's the Big Tower Companies. They bought up the patents to the antenna tilt adjusters to keep us buying their products.

    It's a conspiracy, man.
     
  10. Pushraft

    Pushraft Banned

    I didnt wrongly assume and it is not necessairly better unless you know the optimum takeoff angle you need for a particular contact. It DOES lower the elevation angle to a point on one side but raises it on the other side (as confirmed by WB2WIK who I put a great deal of confidence in). I dont really trust modelling programs anyway as far as radiation plots. Too many unknowns and variables.

    One person even told me that tipping an omni vertical antenna even slightly changes the azimuthal pattern. I first I was skeptical but that seems to be accurate. If you model this in EZNEC the azimuthal pattern gets distorted and actually slightly favors one direction (I think the direction it is being tipped down towards). It probably has something to do with different ground interaction on one side vs. the other. I am guessing on that one.

    Oh and DX being "defined" as long distance communcations by ARRL. I dont really like some of ARRL's definitions because they appear to be abbreviated for convenience at the expense of clarity. If I told someone I drove my car a long way, that may mean different things to different people. Some people like me think driving 500 miles in a day is far but someone else may that is short and think 1000 miles is far. Similarly, someone may think a 500 mile contact is a good DX contact but others may say 1000+ miles is DX. The "definition" is somewhat nebulous and open to interpretation. For someone that is used to using 0.75 mile FRS radios, 500 miles IS very far!

    All interesting stuff though. Fun to debate too.
     
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