DX reciprocity?

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

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  1. AG3Y

    AG3Y Guest

    I still want to encourage you as much as possible, Push! No, I will NOT need the "eight 12 element 20M beams . . . ." to hear you! Many people use QRP radios, feeding a piece of wire thrown into a tree bough to carry on two-way QSOs across hundreds, even thousands of mile distances! It is fairly rare right now, because propagation is generally so bad, but in just a few years time, it will be quite common.

    Please don't put off your schedule. I would still like to encourage you to take the Tech exam sooner, rather than later. No you cannot "skip" the tech exam, but I know of very few people that have failed to pass it after they have made even a half-way honest attempt to understand the rules and theory required for that level of test!

    BTW, I have even heard of guys that communicated hundreds of miles to another station, and then when they finished the QSO, discovered that the bands were so quiet because they had their radio hooked into a dummy load ! It has been known to happen, and not just once !

    Don't make excuses. Show the doubters and nay-sayers what you are really made of!

    73 Jim
     
  2. AB8MA

    AB8MA Premium Subscriber QRZ Page

    Add P=IE, and algrbra, and you can figure out everything. :)
     
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    >Pushraft;1407813]Well as I have stated before, it is quite an elite group. Very knowledgable. Nothing at all like most airhead CBers.<

    ::Well, that's likely true; although there are plenty of not-very-knowledgeable hams also. This is becoming the norm, actually, and has been slowly happening over several years because pretty much anybody can pass the test and it really requires no great understanding of radio, electronics, or anything else. At one time, it did, but those times are gone.

    >I didnt realize there were close to 100 bands I thought there were like a dozen or two.<

    ::Most of our allocated (or I should say "permitted") spectrum is above 3 GHz!

    >My understanding is I have to take both a Tech exam and a General exam I cant just skip the Tech is that correct?<

    ::pretty much. But you never have to get a Tech license at all. The exams aren't by "license class" per se, they're just Elements. Various elements are required for different license classes. You can take them all at once and go from nothing to Extra in one morning if you wish; they do issue the Elements in proper order so if you fail the Extra but pass the Tech-General elements, you become a General right then. If you fail the Extra and General elements but pass the Tech, you become a Tech right then (pending ULS listing, of course, which only takes a week or two). If you pass everything, you're an Extra.

    >If you remember my timeline I stated 2008 was a study year and 2009 I will get licensed.

    Taking jabs at me and saying some of my questions are stupid or not applicable to ham radio or that I am a troll trying to pick the brains of hams to tweak my CB and I will never get licensed is not a good way to recruit newbies.<

    ::I agree. However, remember it is not the job of hams to recruit more new hams. I never found that to work at all, nor is it beneficial to the hobby. People who really want to become hams will, and everybody else really isn't interested. The "not interested" outnumber the "interested" by a lot. Trying to lure the not interested into becoming interested is stupid.

    >I am on my own schedule and dont let people pressure me. I think one reason many people want me to get licensed is so they can find out who I am so they dont have to keep calling me "Push".<

    ::No such thing as anonymity anyway, really. This is 2008, a good hacker can find anybody.

    >Just remember where you all started at. At one point you all knew nothing about radio.<

    ::We were all born knowing very little.

    >It is a very technical hobby. Not everyone has the same goals entereing into it. I am happy to listen in for now on HF.

    In 2009 maybe I can contact some of you but dont expect a booming signal from 100 watts thru an attic dipole.<

    ::I contact guys using attic dipoles all the time. Last night I worked a station in Asiatic Russia using an indoor dipole, on 40m CW. I'm guessing he had a big attic, maybe in an apartment building where one attic runs the length of several apartments. Pretty good signal.
     
  4. Pushraft

    Pushraft Banned

    One other thing I am wondering about reciprocity for both DX and non-DX 2 way communications is this: suppose there is one substantial RF obstruction which is my attic. Let's break this down into 2 cases:

    case 1:

    point to point contact from a VHF (2m) attic antenna to an identical one out in the clear at a land distance such that the signal is about medium quality and there are no other obstruction between them (LOS). Assume identical rigs on both ends or at least very similar including identical mics, same gain rig, similar cable loss, similar noise...

    Is there a difference in reciprocity due to the fact that the antenna in the clear gets an excellent launch and doesn't "see" the obstruction until the last few feet of it's journey, vs. the attic antenna that "hits" the obstruction immediately and possibly distorts it's pattern immediately? Assume the SWR on both ends is similar and low such as 1.2:1 to be "fair".

    In other words, is this a special case where reciprocity doesn't hold? Specifically, is there a bias in one direction vs. the other?


    case 2:

    identical to case 1 except now we are talking about DX on HF (20m). Here, the signal may travel thousands of miles and not "see" any obstructions one way but the other way, it his my attic roof immediately and get's off to a "bad" start.

    It would be very interesting to me for someone with a "killer" DX antenna to find someone with an attic dipole, ask them how many watts they have, then crank his "killer" setup down to match that on the other end of the link. Suppose they both have 100 watts but one has an attic dipole (not fully stretched out like mine), and the other person has a 4 element beam 85 feet up. I wonder if the signal reports would be similar on both ends or if one side has an advantage over the other.

    I also wonder if the results of case 1 and case 2 are consistant. That is, for any 2 given setups, if there is some advantage due to non-reciprocity, if that advantage would apply both to terrestrial links and DX links alike.
     
  5. K7MH

    K7MH Ham Member QRZ Page

    Here is my experience from this last weekend in CQ WW CW contest on 80 meters...not much "reciprocity" in my opinion!!
    I was on 80 during CQWW CW this last weekend. Talk about an exercise in frustration! I could hear EVERYTHING but had a miserable time working almost ANY of it. I worked at it both nights till early morning. The 3X, and the TA's were easy copy early in the evening on the first night as were all kinds of Europeans from about 0300 till about 0800 UTC or so.
    I was running a Pro 3, and an Alpha 99 at 1500 watts to a full size 80 meter dipole at about 70 feet. I was up in Sequim Wa. at about 400 feet overlooking the Straights of Juan De Fuca and the dipole is broadside to the straights. No problem working JA's and UA0 etc. at all. From there, I own Asia! Nothing in front of me at all and just up the slope and a few miles from the water. One awesome view of the straights and Vancouver Island and that is just standing in the yard!
    I did work a few Europeans with some struggle but for the most part they didn't even hear me and I only got the occasional "QRZ" or "K7?" but they went back to calling CQ pretty quickly.
    ...I HATE it!:mad::D But I'll do it again!!!:eek:
     
  6. Pushraft

    Pushraft Banned

    That is one thing I am worried about. That is, I can hear a few "big guns" on my rig but since they have substantially more than 100 watts, I am wondering if they will not hear me on my attic dipole or mobile vertical with only 100 watts. I guess the only way to know for sure is to get licensed and try it or have a local ham try my rig.

    I wonder what the technical explanation of non-reciprocity for DX is. I remember reading in the ARRL book I think that the DX path may not be the same in both directions so maybe that is part of it.

    Also the skip off the ionosphere and the ground or water. I wonder if those slightly favor a particular direction over another direction.
     
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    ::probably nothing to do with propagation and everything to do with the fact that all of Europe is close together than their QRM levels are absolutely incredible. Now factor in that on lower bands like 80m it's common for operators to leave their noise blankers on all the time, which makes the QRM "sound" about ten times worse, as blanker artifacts blanket the band intermodulating with other signals, and you have an absolute mess.

    I've had guys over there "play back" to me what it sounds like on 80m at nighttime in Europe during a contest, and it was a wall-to-wall din of signals. Only those with a lot of experience and skill, and knowledge of how to turn off the blanker and reduce the RF gain, maybe kill the AGC and use an attenuator, can really pick out signals well....

    WB2WIK/6
     
  8. PA5COR

    PA5COR Ham Member QRZ Page

    Only those with a lot of experience and skill, and knowledge of how to turn off the blanker and reduce the RF gain, maybe kill the AGC and use an attenuator, can really pick out signals well....



    You're spot on Sir ;)
     
  9. KJ4AUR

    KJ4AUR Ham Member QRZ Page

    Removed May 07, 2009
     
    Last edited: May 7, 2009
  10. KH6AQ

    KH6AQ Ham Member QRZ Page

    DX reciprocity

    Short answer: Yes.

    Say you are running 100 watts and the person on the other end of the RF link is running 100 watts. You have a dipole and he has a beam. With symmetrical propagation the signal strength is the same at both ends. You're 579 and he is 579. Now trade antennas. You will both notice no difference in signal strength. Paths are not always symmetrical but it is my understanding that most of the time they are.

    So, you hear a DXpedition running 1500 watts and you're running 100 watts. Your signal will be 12 dB or 2-S units lower at his location than he is at yours.

    When someone says "I can work anything I hear" it doesn't mean much, does it?
     
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