DX reciprocity?

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

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  1. Pushraft

    Pushraft Banned

    Good one. Got a chuckle.
  2. W0IS

    W0IS Ham Member QRZ Page

    You mean that real world experience might be more beneficial than theoretical models (whether or not a computer is involved in creating the theoretical model)? :D
  3. G3TXQ

    G3TXQ Ham Member QRZ Page

    So, if you didn't wrongly assume it was "better", why did you compare the difference to people "upgrading their cables".

    Yes, I'd forgotten that if you don't like a definition you feel free to re-define it. I assume from your earlier post that the Push definition of DX is any contact made via an ionospheric path. [Push says: "DX in this hobby means distant contacts which I interpret to mean contacts that can be made farther than with just terrestrial paths and using the atmosphere for assistance"]

    By the way, don't confuse atmosphere and ionosphere - they're two different things.

    Well at least you put EZNEC into action and learned something.

    PS still waiting for the URL

  4. KL7AJ

    KL7AJ Ham Member QRZ Page

    H.F. propagation is DEFINITELY non-recoprocal, unless you happen to live at the precise magnetic equator....about as likely as a politician uttering a truth. I go into great detail on non-reciprocal propagation in Chapter !7 of the Opus, "Bent Radio."

  5. N5KRC

    N5KRC Ham Member QRZ Page

    Your just the kid looking in the window at the candy store, wondering how all that candy is made.

    The people who get to claim this as their hobby are the ones who made sacrifices, invested time and money, and spent an ungodly amount of time testing and experimenting to get where they are.
  6. W0IS

    W0IS Ham Member QRZ Page

    Nah, he's starting out like most of us did. At this point, his hobby is "SWL'ing", a fine hobby in its own right.

    Actually, Push should print up some SWL cards and start sending them out. He can even sign up on eQSL.cc as an SWL:


    He can send an envelope to the SWL QSL bureau and get his paper cards:


    Push, if you hear me on the air, just let me know and I'll send you an SWL card.
  7. KL7AJ

    KL7AJ Ham Member QRZ Page

    More like looking in the butcher shop wondering how hot dogs are made. Some things you just don't want to know.
  8. W8JI

    W8JI Ham Member QRZ Page

    Nonsense. If you look at the absolute level of signals, which is the only correct way to do it, the only thing tilting an antenna array of reasonable size close to the earth does is very slightly alter the gain. You might give up a tiny bit of low angle gain to favor higher angles by tilting, but you can never increase low angle gain by downtilting any more than what the array does when it is anywhere close to zero elevation tilt. The overall gain peak barely changes.

    For example a 47 foot three element 40 meter yagi at 125 feet above ground has the following:

    25 degree up tilt
    25 deg = 9.15 dBi
    15.5 deg = 13.36 dBi peak
    5 deg = 7.34 dBi

    If we swing it 50 degrees lower in the front to a 25 degree downtilt, we have:
    25 deg= 10.33 dBi
    16 deg = 13.38 dBi peak
    5 deg = 7.0 dBi

    We actually lose low angle gain by downtilt, because we try to force the reflection to aid radiation when it is trying to null radiation, so earth losses increase. We are pointing the antenna into a lossy reflector.

    The zero tilt antenna would have:
    25 degrees = 9.14 dBi
    15 deg = 13.62 dBi peak radiation
    5 deg = 7.86 dBi

    We will always have an insignificant lowering of wave angle, an insignificant change in maximum gain angle, but we can have a little increase in higher wave angles. This is because the height above earth, exactly as the fellow from England said, sets the wave angle. Not the tilt.

    I would certainly place my money on a model long before your power of deduction or reasoning.

    Anyone who says a typical size and height HF antenna's wave angle can be substantially controlled at lower angles by tilt is absolutely wrong. That's a fact.

    If you stack two antennas some distance apart large in terms of wavelength you can move elevation nulls around, but you can never really change the maximum gain point of the system lower than the value for the two antennas combined in phase. You can increase the high angle gain, but never increase the lower angle gain beyond the in-phase peak.

    99 % of the time maximum signal from my 40 meter stack is with all the antennas in phase. On a very very rare occasion with a very close staion in the daytime, some other combination that increases wave angle might help.

    It is so rare to see a change, I never use my "lower/upper/both in phase/ both out of phase" switch. It sits in the both in phase position all the time.

    That's how it all really works.

    73, Tom
  9. Pushraft

    Pushraft Banned

    Actually kinda like that kid in Home Alone who asked the van driver, "Does this thing have 4 wheel drive?, does it get good gas mileage?..." and the driver's response was "Gee I dont know kid, beat it!".

    Sometimes I feel like that is what is happening here but I put these questions out there hoping that at least one person will give me the answer I am looking for.

    It seems kinda foolish and wasteful for newbies to go thru all the same extensive testing when someone else that did the same thing can just tell him what to expect. One slight flaw with that is any little change in the test can produce different results. Another flaw is many times details are left out or there are other factors such as conditions.

    I am very curious as to how some things about radio work and this forum has given me a good place to inquire. My interest in radio is holding steady although I dont feel an overwhelming desire to Tx as I am content to Rx for now and try ot find ways to reduce noise and improve signal. That is a challenge too.

    As I said before, if I can hear people strongly, then even if they are using 1500 watts, they should be able to hear me with my 100 watt rig although in theory, about 12dB down from them or 2 full S units down. But if my noise from my indoor antenna is 2 S unit higher than theirs, then it should be a "wash" or "even Steven".

    One of the frustrating things about DX "work" compared to ground "work" is that the ground stuff is more predictable and much less dependant on conditions. That is, if an FRS radio goes 1/2 mile one day between 2 houses, the next day it should still go that same 1/2 mile. It doesnt matter much if it is sunny, rainy, snowy... But I guess if amateur radio was a "constant" it wouldn't be as interesting. It sure would make antenna testing a lot easier though.

    Someone mentioned using different Rx and Tx antennas. My Yaesu rig is already set up for that as it has a pair of RF ports. The main SO-239 is for both TX and Rx unless I push a switch on the back then the alternate RF in port becomes the Rx port exclusively but Tx gets router out the SO-239 and the RF in port gets closed while Txing via an internal diode switch of some sort. That feature may be useful for me to control noise. Maybe I can just hang a vertical wire out of my 22 ft high window for Rx to keep the noise down and eventually when I get my ticket, use the attic dipole for Tx.

    Does a noise antenna environment affect Tx is a bad way or is that 99.99% on the receiving end. That is, can the signal pick up noise on the several thousand mile journey and show up as noisy even in a quiet Rx environment?
  10. G3TXQ

    G3TXQ Ham Member QRZ Page

    Push - hurray, at last you've admitted it! It would save us a whole lot of time if you just told us at the start what answer you were looking for ;)

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