OCFD REALITIES

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2. The Performance of a Good OCFD seems on

    Par with that of an  Openwire - Fed - Dipole

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I'm sure this statement will meet with a lot of opposition, especially from many of the life-long users of openwire-fed dipoles (like me), but In My Honest Opinion, it is true.

First let's agree on how we are defining performance.

IMO, there is only one real-world measurement that counts:

The ability of my signal to bend the S-Meter's needle

(in a positive direction) at the other end of the QSO.

 ALL other claims, such as:

• "x" fraction of a dB more gain
• "y" fraction of a dB less feedline loss
• etc., etc., etc. ...

are meaningless things, perhaps good for bragging rights, but nothing else!

BASED ON THE PERFORMANCE DEFINITION ABOVE:

After about 40 years of using openwire-fed dipoles, and now 7 years of using

a properly designed  and built  OCFD,   I  have reached  the  conclusion  that

there is no perceivable difference in the  performance of these  two antennas.

    As with all compromises, there are trade-offs to be accepted:

• You can no longer brag about using 100-year-old openwire technology.

• You can no longer brag about the very expensive antenna matchbox required to match your antenna to 50 Ohms - because you don't need one.

• With your coax laying on the ground, you can no longer pester your neighbors with the sight of ugly (in their eyes) openwire feedline running through the air. 

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3. What Some Experts apparently don't want to understand:

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In reading magazine articles and books written by antenna experts much more knowledgeable than me, I often shake my head in amazement at the author's out-dated view on the OCFD antenna.

Here are my problems with them:

• They are quick to point out that the OCFD, by nature, is prone to a lot more common mode current trouble than an ordinary dipole or vertical antenna. (Duh!)

• It is clear from their comments that they have never recently even attempted to study the problem and see if they can find a cure.

• They don't appear to [want to] understand why a normal OM and YL would even look at an antenna like the OCFD.

• They always seem to assume that every ham on the planet runs 1500 Watts! 

• They always seem to assume that every ham on the planet lives on a ranch or farm with lots of room for multiple antennas, and  has no HOA's or nosey neighbors.

• They never suggest an alternative antenna for someone who wants to (or must) cover as many bands as possible with just one single antenna.

Other than those points, I have no issues with these guys.  :-)

In one particular case with an expert living in California - whom, BTW, I (otherwise) highly respect, we have debated this issue many times and each time it ended in the same way:

• I asked the OM to suggest an alternative, single radiator antenna that we could use on almost all HF ham bands.

• He vanished from the discussion.  No answer!

Message to the "Experts":  

It ain't what you don't know  that gets you in trouble.

It's what you know for sure that just ain't so. - Mark Twain     

  As with all compromises, there are trade-offs to be accepted:

• These guys don't like me anymore.

• (Ask me if I care.)

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4. Summary and Bottom Line

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The OCFD is not a Wonder-Antenna, it's just a Good Multi-Band Antenna.

Like all antennas, it has advantages and disadvantages.

Im many cases, its advantages far outweight its shortcomings.

Also, like all horizontal antennas, it's performance is highly dependant on its height above ground - especially on 80m- and its installation being as free and clear of surrounding objects as possible.  Less than optimum installations will give less than optimum results.

Advantages:

• One single antenna that will cover almost all HF bands.
• Lowest cost/band of any good multi-band antenna!

• Low profile, important to those of us living in the city.

• SWR generally well under 3:1 on most bands, except for 80/75m where fractional bandwidth limits its usable range without the aid of an antenna matchbox.  (This is typical of all 80m antennas).

• Performance on par with that of a dipole.  (A standard 80m dipole has the same fractional bandwidth problem as the OCFD).

• Performance also on par with that of an openwire-fed-dipole.
• No need for an expensive matchbox.  The transceiver's built-in ATU will suffice for minor pruning of the SWR.

Disadvantages:

• The SWR is not the same on all bands; it varies from one band to the next.

• The frequency of resonance is not independantly adjustable by band.  It is what it is and must be accepted as that.

• The off-center feeding results in a significant increase of common-mode-current trying to flow down the outer shield of the coax.  It has been shown that with proper choking, this can be held in check, at least for moderate power levels up to 1kW.  HERE

• There doesn't seem to be an easy way to cover ALL HF bands.  17m and 30m seem to be mutually exclusive, without resorting to a more complex solution. 

• I haven't personally investigated 60m and have yet to see where anyone has managed to show a single-radiator OCFD working on most HF bands, and 60m.

• Almost ALL commercial 80m OCFD antennas* are built with insufficient common-mode-current choking.

• Thus I cannot recommending buying them.

• BUILD YOUR OWN!

*EXCEPTION

THE BOTTOM LINE:  Though not a wonder antenna, the OCFD, when built to the correct design, using a good enough balun, is almost a wonder antenna for city dwellers.  It can enable its owner to radiate a good signal on many bands, without the need for an expensive antenna matchbox, yet maintains a low profile, compared to other multi-band antennas.

If you hear of someone unsatisfied with their OCFD antenna, then (s)he probably bought it commercially or built it using the wrong balun.

MORE INFO:

To learn more about these OCFD antennas, please

join our OCFD group on groups.io:  OCFD GROUP

And, learn more about OCFD Antennas,

here: OCFD-Hamwaves