A Born Again Miracle Whip

About 20 years ago a Canadian company, based in Quebec, produced a compact QRP antenna called the Miracle Whip. It was a really good piece of engineering that relied on the principle that a short whip has capacitive reactance that can be cancelled by feeding it through an inductive reactance. Remember, resonance occurs when capacitive and inductive reactance are equal.

The design employed a switched variable inductor with multiple gold-plated contacts feeding a 57-inch telescoping whip and was intended to tune from VHF up to and including all the HF bands as far as 80 meters.

But it had limitations

The short whip resulted in a very high Q so that careful selection of one of the multiple switch settings was necessary. That also meant that bandwidth was limited without resetting the variable inductor. It was intended to be used with Yaesu’s FT-817 at a maximum of 5 watts output power. So combining low-power, a short inefficient whip and narrow resonant bandwidth meant the Miracle Whip wasn’t quite the miracle its name suggested.

Miracle Whip variable inductor

Before it went out of business, the company’s product range expanded to include a version without the whip. In its place was a way of attaching a more efficient radiator while retaining the excellent variable inductor. I was way ahead of the curve. I had bought a Miracle Whip and quickly decided that its limitations could be overcome by rebuilding it to accommodate a longer whip (such as the 17ft MFJ-1979) or even a wire antenna. The multi-position switch had a bypass setting to allow use of a resonant radiator. For example, the MFJ-1979 is nominally resonant on 20 meters but could also be used on 40 meters by using the Miracle Whip’s variable inductor.

The Sun Ain’t Gonna Shine Any More?

And then the Sun went into the dormant sector of its 11-year cycle and I set aside my QRP gear. The modified Miracle Whip languished in my junk drawer for many years until my interest was re-awakened at the start of solar cycle 25.

I have read several recent accounts, written by fellow ham bloggers, of successful deployment of very short HF antennas at QRP power levels. The popular Elecraft AX1 and AX2 seem to be attracting a lot of interest. So I dug deep into the bowels of my QRP equipment graveyard and pulled out my old Miracle Whip to see what I could do with it.

Born Again

The Elecraft AX1 and AX2 use 48-inch whips while the original Miracle Whip came with a 57-inch whip (to enable its use on the 2-meter band). My original 57-inch whip was unserviceable and I had already replaced the plastic enclosure with a slightly larger one fitted with a 3/8×24 mount on top.

Over the years I have accumulated a small collection of short whips of various lengths and among them I found a 48-inch stainless steel whip – unfortunately not telescopic – with a 3/8×24 fixture. Just the job!

Near Field Radiation Jeopardy

Just like the Elecraft AX1 and AX2, the Miracle Whip was originally intended to be affixed directly to the transceiver. Since it was designed to be paired with the Yaesu FT-817 it had a male PL-259-type connector to mate with the FT-817’s rear antenna connector. This resulted in a significant near-field RF exposure issue.

Alright, I’ll admit that near-field RF at QRP power levels is not a significant risk to humans. But, as I learned when playing with the Miracle Whip 20 years ago, near-field exposure risk is certainly not insignificant to electronic equipment.

Back then I was a PSK-31 enthusiast and had purchased a radio/computer interface from a very small vendor in Australia. When I used my FT-817 with the Miracle Whip attached to its rear antenna connector, the interface circuit became very unstable. I contacted the vendor who advised me that the probable cause was RF getting into the unshielded interface electronics. He suggested moving the antenna further away from the radio.

I followed the vendor’s advice and the problem was solved. Mounting the radio/computer interface circuit inside an Altoids tin also made a difference. Since that experience I have been very wary of RF getting into electronic circuits.

Elecraft recommends using radials with its AX1/AX2 antennas. The “other half” RF current has to go somewhere and if there is no counterpoise, the radio chassis, microphone cord or CW key become RF radiators. The phone you might be using for logging will be picking up your signal. Your callers may inquire about the loud buzzing noise they can hear on the call.

Keep Fido safe!

So let’s say you mount your choice of short whip antenna directly to the radio and install radials as suggested. They will radiate RF and your legs, feet and maybe your dog will all be exposed to RF and high voltages. Wanna risk Fido? I wouldn’t.

But, it doesn’t end there. Human flesh easily absorbs RF and while (at HF) it may not ionize and destroy the cells of your body, your body will become part of the antenna! If you know how to model an antenna with 200lbs of human flesh acting as a reflector please let me know in the comments.

Banish the Whip

So where is the advantage in mounting a compact, short whip antenna directly to the radio? Why risk all the unpredictable consequences of deliberately putting yourself, your electronics – and Fido – in the near-field radiation zone?

Far better to banish your antenna to a location at least a few feet – and preferably more than a quarter wavelength – away where EZNEC can reliably predict the propagation pattern and man’s best friend won’t be spraying RF around as he wags his tail.

Just a Novelty

Even though I am now back in the QRP fold I probably won’t be using my rebuilt Miracle Whip very often. It’s more of a novelty item than a valuable addition to my antenna bag. Maybe some day when propagation conditions are good, I might mount it on a ski pole stuck in the ground at least 25 feet away from the rest of my station. I am an avid experimenter but I don’t mess around when I’m out in the field filling my logbook.

Why use a 4 foot whip when a 17ft whip – or a half-wave wire – will get the job done no matter how many spots are on the face of the Sun today? Miracles don’t happen every day.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s