Miracle Whip with Icom 703....any good?

Discussion in 'Amateur Radio Equipment Reviews' started by KC8TBY, Nov 9, 2008.

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  1. G4ILO

    G4ILO Ham Member QRZ Page

    I had a Miracle Whip and it is a nice portable receive antenna and it is possible to make contacts with one but it is really hard going. I sold it a while ago but being a glutton for punishment with more money than sense I decided to get another one except this time I went for a UK made equivalent called the Wonder Wand.

    I recently tried an experiment switching between the Wonder Wand and another short portable QRP HF whip called the ATX Walkabout which I think is sold in the US by MFJ. I used WSPR, a low power beacon mode which enables you to get accurate reception reports from all over.

    The ATX is a more conventional design using tapped base loading coils. It needs a resonant counterpoise and I used a steel tape measure. Both antennas were mounted on the back of an FT-817 sitting on the desk here where I am now, so it is a similar situation to what you are contemplating.

    The ATX was so vastly superior to the Wonder Wand that it is debatable whether it really deserves to be called an antenna. It's a pity I didn't have the chance to perform this same test on the Miracle Whip but I doubt if the performance would be much different as they both use the same design principles.

    So if you are going to do this, forget the Miracle Whip and get an ATX and a steel tape measure. On the other hand, if you really want to make contacts get an MFJ magnetic loop and mount it on a stand. It's a lot of money but it's the next best thing to a full sized outdoor antenna.

    If you can't afford to buy a magnetic loop try making one. It's not too hard for QRP. It's when you want to run 100W that it gets difficult because it's hard to get tuning capacitors that won't flash over.
     
    Last edited: Nov 9, 2008
  2. G3TXQ

    G3TXQ Ham Member QRZ Page

    I do not accept this.

    I have modelled the test set-up as described using their reference antenna, a 10ft centre-loaded whip, a 5ft centre-loaded whip and a 4.3ft base-loaded whip, all tuned against the sloping counterpoise. At a 3 degree elevation angle there was less than 1db difference between all 4 antennas - it hardly sounds "length dependent" to me. The shootout measured the Miracle Whip as 10.6dB worse than the reference antenna, so what accounts for the remaining 9.6dB? Even assuming the 0.75dB measurement accuracy worked against the MW, you're still left trying to explain an 8dB shortfall in performance.

    Steve
     
  3. M3KXZ

    M3KXZ Ham Member QRZ Page

    Steve, could you let me have the R and X values for the loading so I can look at this further as well.

    Note, I did accept that there's a big difference between the very short (1/16 wavelength) antennas and the medium to long antenna (1/8 and longer). But without measurements of the whole of the RF field then nothing can be concluded about radiation efficiency from the test and the result. The test, as is, can do no more than differentiate between antennas at one elevation angle and where there is a SIGNIFICANT difference in measured RF.
     
  4. KA5S

    KA5S Premium Subscriber QRZ Page

    I ascribe the shortfall to a poor choice of toroid material; at one of the shootouts, an antenna the same length, built in the same manner, but using a wirewound potentiometer as the "inductor" BEAT a "Miracle Whip."

    Cortland
    KA5S
     
    Last edited: Nov 9, 2008
  5. SM0AOM

    SM0AOM Ham Member QRZ Page

    "Artificial aerial licence"

    It has been said that the "Miracle Whip" is about the closest you can get in actual operation to the device prescribed for the pre-war "artificial aerial licence", which can be "Googled" for your enlightment...

    73/

    Karl-Arne
    SM0AOM
     
  6. M3KXZ

    M3KXZ Ham Member QRZ Page

    Here's a simple exercise that I hope might explain it a bit (but until I have R and X values it excludes loading on the antennas and just assumes they can be matched ok at 100% efficiency).

    By setting up a Near Field table in EZNEC you can predict the signal strength at any given point. The Far field table is only valid once ground wave has decayed to zero (I learned this from what Roy Lewallen has written here
    http://newsgroups.derkeiler.com/Archive/Rec/rec.radio.amateur.antenna/2005-09/msg00471.html ) and I doubt ground wave has decayed to zero at a distance of 80m. It's possible to obtain a prediction of the NF signal strength (V/m RMS) at distance of 80 meters and height of 6.25m (20ft) from the antenna.

    By setting the input power to the antenna at 10W, the predicted signal strength for the 1.34m (4.3ft) tall antenna is 0.0205864 V/m RMS. The predicted signal strength for the 5.16m (16.5ft) tall reference antenna is 0.260435 V/m RMS. This is a difference of x10.38, or in terms of dB, the difference in signal strength at this point is 10.16dB.

    There you go!

    But furthermore, if you repeat this for much higher angles(over 40 degrees), the predicted V/m RMS for the short antenna is higher than for the reference vertical. Which is why a measurement at one point, with the same counterpoise for both antennas, will tell you nothing about the radiation efficiency. It will only tell you about the signal strength at that point for different antennas over that particular counterpoise. UNLESS you are comparing two antennas of the same length but with different methods of loading/matching then nothing can be determined about efficiency.
     
    Last edited: Nov 9, 2008
  7. M3KXZ

    M3KXZ Ham Member QRZ Page

    Cortland, the remaining difference to find is that between the MW and the short WW of approx 3dB, and this could be due to the core. It would be interesting to see if this is consistent on other frequencies as well, or if the MW is a good compromise.
     
  8. G3TXQ

    G3TXQ Ham Member QRZ Page

    Peter, firstly I own up to having been looking at Far Field rather than Near Field, so I just re-ran a few models looking at the NF at the test receiver position.

    My reference Tx antenna was exactly as described - 16.75ft vertical and 16.75ft counterpoise using #14 copper.

    Then I shortened the vertical to 10ft, made it 0.5" diameter aluminium, and found I needed a centre-loading coil of +j460 Ohms to resonate it at 14.1MHz.

    Then I shortened it to 4.3ft and needed a base-loading coil of +j612 Ohms.

    In neither of the loaded cases did I include coil losses because the point of the exercise was to see what difference height and loading position alone made.

    Taking Near Field Ez values 262ft away and at a height of 20ft, the 10ft centre-loaded was 2dB down on Reference and the 4.3ft base-loaded was 6.7dB down on reference. That's explaining a big chunk of the 10.6dB, but there's still 4dB "missing".

    By the way, I think you forgot to use 20Log (not 10Log) in your earlier signal strength calculation.

    I'd be interested to see if you can confirm my numbers.

    73,
    Steve
     
  9. W0IS

    W0IS Ham Member QRZ Page

    I have to admit that I have no experience with the Miracle Whip (or any other purchased antenna), so take the following for what it's worth.

    It seems to me that there's nothing particularly miraculous about the design. It's just a relatively short whip with an inductance at the base. It will certainly radiate some RF. But in general, you don't get something for nothing. Because there's very little metal radiating RF, it probably won't work particularly well.

    It will probably work pretty well on 10 meters, since at that frequency, the length starts to become a non-trivial percentage of a quarter wavelength.

    My main issue is the cost. In what seemed like a marketing coup, the design was in a QST construction article in the very same issue as the first ad for the commercial version. The commercial version is very expensive, and any antenna that short is not going to work very well. In fact, I seem to recall that the construction article more or less conceded that it would work, but not particularly well.

    It seems to me that for the original poster's situation, a much better solution would be some sort of temporary wire antenna. This could be as simple as a quarter-wavelength piece of wire (e.g., 16 feet for 20 meters) with a banana plug at the end. Plug the banana plug into the coax jack, string it around the room as best you can, and start operating. I'm guessing this would be just about as fast as tuning up the Miracle Whip.

    Another 16 foot wire could be strung from the ground terminal of the radio to act as a counterpoise/other half of the dipole.

    This wouldn't be an ideal antenna, but I'm willing to bet it would work a lot better than a Miracle Whip, at considerably less cost.
     
  10. M3KXZ

    M3KXZ Ham Member QRZ Page

    Steve, I'm working on it at the moment and will post back after work tomorrow. I might have cocked something up!
    Pete
     
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