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From the July 2007 issue of CQ magazine.



DWM “Yo-Yo Tenna”
Link to Original Article on MonitoringTimes.com
By Bob Grove W8JHD

When you’re operating VHF/UHF portable, it’s really no big deal to find an adequate antenna. Resonant elements are short, and a gain antenna doesn’t require vast expanses of real estate. But for the HF ham operator or shortwave listener, a resonant element can easily be 60-100 or more feet in length, and a multiband antenna can impose a daunting challenge. Often, a transmatch (“tuner”) is employed to cancel the reactance of an impedance-mismatched antenna system.

And what about restricted apartments, camping locations, business trips, or even Field Day? And how about long-distance emergency comms after a natural disaster or other unforeseen event? Wouldn’t it be nice to have a compact HF antenna that folds up to a few inches to fit in a pouch?

The military has done it in the past with interchangeable elements, inductively-wound elements, or even reeled metal tape measures which can be unfurled to an appropriate length for the band chosen. Perhaps it’s the latter approach that may have inspired this interesting product from DWM.

Multiband Antenna to Go

The dipoles are assembled around pairs of enclosed, fishing-style reels which resemble a “Yo-Yo,” as first observed by Jeffrey Lauterbach, the son of DWM’s owner, Bill Lauterbach (WA8MEA). Each reel can release up to 40 feet of insulated, stranded, #22 wire; a pair can effect a dipole for 40-meter operation (7 MHz), or shorter for higher-frequency bands up through two meters (148 MHz).

The basic “Deluxe” pair YYTD-259 includes a pigtail PL-259 male connector for transceivers; the YYTD-PHN is equipped with a 1/8” (3.5 mm) phone plug for popular multiband portables like most Radio Shack, Sony, Grundig and Sangean radios; and the YYTD-RCA provides an RCA phono plug for models like the Sangean ATS-803 and Radio Shack DX-394, DX-440 and some older receivers and transceivers. All “Deluxe” models are $29.95 each plus $7.95 shipping.

For multiband operation, the new, four-reel, dual-band, model Yo-Yo-Vee model 4 ($49.95 plus $7.95 shipping) or six-reel, tri-band, model 6 ($59.95 plus $9.95 shipping) may be in order. The multiband pairs of reels are connected to a popular Budwig center insulator affixed with a standard SO-239 female “UHF” connector for transmission-line attachment.

If you have a transmatch handy, you can trim the VSWR very low, even on lower frequencies than 7 MHz. Or simply use the transmatch with the basic YYTD-259.

The Budwig insulator also has a center hole to support the dipole and relieve the strain on the deployed wire.

Erecting the antenna

The reels are encapsulated, not open, to resist moisture intrusion and prevent unraveling. Each reel has a handy, molded loop to facilitate tying it to a support (tree limb, building eave, pole hook, etc.). When erecting both ends of the dipole, you will need to provide lengths of tether cord; these can be used to tie down securing stakes for the poles as well.

A tie-off tab is provided on each reel for wrapping a turn of wire to keep it from unraveling further once the proper resonant length is established. The reel is equipped with a spinner knob which assists in both deploying and spooling the wire.

The six reels which comprise the tri-band dipole are colored by pairs, assisting the operator to equalize lengths on each side of the center insulator. Actually, this isn’t really necessary since all three pairs are electrically connected to the same point on the center insulator, but it’s a thoughtful touch.

While the small-gauge wire may appear skimpy, it is sufficient for both receiving and transmitting (100 watts or so).

If you don’t have trees or eaves to support the dipole, you will need to provide masts. DWM suggests telescoping lengths of rigid PVC; it’s strong, cheap and lightweight. Try to get it up as high as possible, since a horizontal dipole will react reflectively with the ground, distorting the radiation pattern to favor overhead instead of the desired horizon.

It’s best to feed the antenna with lightweight RG-58/U coax; larger-diameter, heavier RG-8/U will provide no significant improvement except when in very long runs (well in excess of 100 feet) at HF.

And one final tip: You may wish to measure off correct lengths for the band(s) of operation, wrapping a small piece of contrasting-color tape at those points, or brushing on a swath of paint. This makes it much easier to deploy the right length of wire in the field.

For more information including ordering, contact DWM Communications, P.O. Box 87, Hanover, MI 49241; or phone them at (517) 563-2613 (orders) or (517) 563-9022 (business). Email: tinytenna@hotmail.com or visit their website: http://qth.com/dwm.
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