Using FT8 to demonstrate Antenna Orientations

Discussion in 'Amateur Radio News' started by KM9G, Oct 6, 2021.

ad: L-HROutlet
ad: l-rl
ad: HRDLLC-2
ad: abrind-2
ad: Left-2
ad: MessiPaoloni-1
ad: L-Geochron
ad: Left-3
ad: L-MFJ
  1. W1YW

    W1YW Ham Member QRZ Page

    Cornelius,

    Please read my comments with greater care. I already stated that there are other ways of testing for power patterns. The one I presented-- 'A/B' comparisons with an RF attenuator for RSSI-- is the one most relevant to the observation that KM9G was making in the OP. Its not elegant at all. Its just one that removes systemic errors, avoids unscientific use of variables and unknowns, and allows greater precision than an S meter, or an FT8 SINR value, alone.

    Apparently using this method in ham radio is more common than you think: MFJ sells an attenuator (MFJ-762) that it advertises for just this purpose. So some folks do this method. Just few, if any, on this thread.

    To wit the MFJ-762:

    "Plot accurate antenna patterns -- connect it between you receiver and antenna and use your S-meter as a precision calibrated field strength meter"

    You can get used rotary precision attenuators at ham fleas for a fraction of the price of new.

    Is this method a 'best practice' for the case being considered? Yes, it is. That is why we don't follow cow paths to Rome, or ancient dead ends, but take major hiways--or hiway in this case.

    73
    Chip W1YW
     
    Last edited: Oct 10, 2021
    M1WML likes this.
  2. W1YW

    W1YW Ham Member QRZ Page

    Classic "cancel-culture".

    Sorry Mindy. I will continue to enjoy ham radio and my fellow hams, and contribute to the enhanced knowledge base of the service for the forseeable future. Sorry you are having a bad day.

    Please stay to comments relevant to the topic, and not attacks of an intentionally personal nature. This is not CB. Hams should not act like (the negative aspects of) CB'ers.

    Just 'chill'... Roger? (BTW, I have a farm in KY and have enjoyed hillbilly swimming pools many,many times. It is a clever solution when bears want to tear up your hot tub. An F-150 is de rigeur.)).

    [​IMG]

    Wishing you the best.

    73
    Chip W1YW
     
    Last edited: Oct 10, 2021
    M1WML, N3RYB and W0PV like this.
  3. OE4KSF

    OE4KSF Platinum Subscriber Platinum Subscriber QRZ Page

    Should I allow myself to say a few more words about this by testing changes on antennas etc, when you only have one to compare with::
    I have knocked down 3 x 2 meter long copper tubes as earthing points at the base of my vertical - and initially connected these to the ground plane on the antenna.
    Thought mostly about any lightning strike or static charge in the antenna.
    It is 26 meters high.
    Then read that this might not be the best thing to do. Tried to disconnect - run back to the radio, test - then run back to the antenna and reconnect etc, but it did not make sense.
    By the time I spent making these changes, conditions had changed - and my relative testing on the S meter did not make sense.
    Therefore, I connected a larger car-light relay (can handle large power, but not so high voltage) - and pulled a power cable into my shack. Then I could easily connect the earthing in and out while listening to a remote station. Found out then that this grounding was actually a somewhat good thing at higher frequencies, but did not do anything at lower frequencies.
    It was therefore removed.
    Same thing, I wanted to insert a 100K resistor as a bleeder for static. Used the relay again and found that connecting it to the screen / ground on the coax did not make much difference, but when I connected it to ground rods, it got much better. ( got rid of close to all on 160m)
    I could test it all out by using the relay - and connect it on and off in real time.
    Again - the conditions change so fast (at least at higher frequencies) that one must be able to test either on two comparable systems at the same time - or in my case here - be able to turn on and off in a very short time to be able to compare.
    NB! This I found in my settings , ground conditions etc etc - and my not be the same at your place and conditions
    73 - Knut
     
    M1WML and W1YW like this.
  4. KM1H

    KM1H Ham Member QRZ Page

    Radiating coax can be a good thing for TX but the flip side is that it does very well as a receiving antenna for all the local noise. In the past, local pre noise generators and ferrites, hams used a radiating coax without realizing it.
    The EFHW alone can also be a very noisy receive antenna even with a ferrite choke(s).
     
    M1WML and W1YW like this.
  5. K2ENF

    K2ENF XML Subscriber QRZ Page

    I don't recall making such reference, so I'll assume it was someone else in the thread.

    On second glance, I suppose you're suggesting that the height of the mast means the oax becomes a better radiator. And I suppose that would be true, if the antenna were not solidly tied to the ground system at the TOP of the pole. Additionally, I'm running chokes on ALL my antennas, including the IMAX. So, I'm unclear how much radiation is actually happening common mode.
     
    Last edited: Oct 10, 2021
    M1WML likes this.
  6. W1YW

    W1YW Ham Member QRZ Page

    You mentioned (post #75) that the antenna works well outside of the band it was made for. In those cases, radiating coax happens, and is the reason why tuning is relatively easy. If you had put a line isolator ( a very good choke system ) at the feed you would not see such out of band performance.

    73
    Chip W1YW
     
    M1WML likes this.
  7. W1YW

    W1YW Ham Member QRZ Page

    Yes.

    That's it.

    And when the ground system is raised above ground and is not isolated, it can and does radiate (at those other bands).

    I have always been astounded how coax, for example, wants to radiate:) Oftentimes a large number of ferrite collars are needed to provide enough reactance to stop the coax from radiating. More than logic might suggest.

    The easy way to tell if the ground line is radiating (at the out of bands mentioned) is to take a field strength meter near the ground system , above the ground.

    :)

    73
    Chip W1YW
     
    M1WML likes this.
  8. OE4KSF

    OE4KSF Platinum Subscriber Platinum Subscriber QRZ Page

    One more thing - I had 4 different antennas for 10 meter up. And used a coax switch to select them.
    Found that when one was working best one day - it could be the opposite the next day. Vertical vs horizontal etc
     
    M1WML and W1YW like this.
  9. K2ENF

    K2ENF XML Subscriber QRZ Page

    While true, have a look at the second para that I added after the fact.

    The thing is noted in many circles as being a very wide-banded beast.

    Observe for example....

    https://wb3anq.com/the-solarcon-i-max-2000/

    So that means that the I-MAX 2000 is a 5/8 wave antenna on 11 meters, (27MHz CB band) as advertised.

    But on 10 meters, it works out to a sweet .64 wave antenna. This is a very good thing. And it just so happens that the unique length of this antenna turns out to be a virtual nice little 1/2 wave on 15 meters. With 17 meters being close to 15 meters, the I-MAX 2000 will load up nicely there too with an antenna tuner. The antenna is wide banded enough to cover 12 meters very well also.

    Don't misunderstand, I'm not being critical of your point, here except to say that the design of this imax means that common mode radiation is less a problem than with most out of resonance operations, because it does in fact resonate on bands outside the original design criteria. In this (specific) case that doesn't even come into play for this unit until you get to perhaps 17m and beyond. Even at 6m, you're dealing with about a 2.7/1 match, because I suppose of it actually resonating fairly well on 12m (About 2/1) . That means at 6m you're getting perhaps 11 or 12% of your TPO bounding back down the coax?

    (HA! OTOH, I have a random wire on a 4/1 that raises serious hell with my shack...... It's coming down today)
     
    Last edited: Oct 10, 2021
    M1WML likes this.
  10. W1YW

    W1YW Ham Member QRZ Page

    Yep. All sounds good.

    Maybe someone wants to NEC model that antenna to see how it works on the other bands. If you don't measure the SWR predicted (by modeling)at the other bands, that's a pretty good, but not infallible, rule of thumb that the coax or ground line is part of the radiating system (and hence contributing to the different SWR from the model) at those other bands:)

    73
    Chip W1YW
     
    M1WML likes this.

Share This Page