SMA-F Rat Tail on IPX6-F Antenna
A simple but significant, and inexpensive improvement that can be made to the Smiley HT antenna SMA-F and SMA-M bases we sell is the addition of counterpoise from a device commonly referred to as a "Rat Tail". The effectiveness of a counterpoise element is not a myth, it is pretty simple science and therefore not about to make anyone millions. Technically, counterpoise is is not a true ground plane, it would more accurately be referred to as a 'virtual ground plane'. You may have seen radial elements at the bottom of a base station antenna on a roof somewhere, and these are there to give counterpoise. So in the case of a rubber duck, counterpoise gives a virtual ground plane reference to trampoline the signal using the same dynamics analogous to what radials do for base station antennas.
First it worth noting that while a half wave antenna does not require a ground plane, an antenna that can reference a ground plane such as a 5/8 wave has better propagation. Our 5/8 wave is a base loaded 1/4 wave that radiates a 5/8 radiation pattern. That fact is germane to the antennas we stock. It is also worth noting that a Rat Tail will significantly render the 1/4 wave model 270a dual band telescoping antenna into a 1/2 wave dipole on VHF.
These have been bench tested by Smiley and they have found that while this Rat Tail does introduce a ground plane, it does not increase, or decrease SWR. If you are already on a resonably good ground plane, then the Rat Tail would not demonstrate a noticable improvement on signal characteristics. But, you never are on that perfect ground. We have found subsequent to subjective field testing in environments where Guides often find themselves: on water, ice/snow, or porous regolith, means the ground you're standing on often acts as a capacitor with regards to your radio signal. Thus the counterpoise element can increase your transmit range exponentially because it introduces the all important ground reference that is needed for efficient signal propagation required by the vertical tuned element in monopole antennas. Our users have also reported they have seen a significant improvement in receive after deploying a Rat Tail as well.
We make these using a 1/4 wavelength* piece of silicon #18 stranded copper wire, and soldered to the metal Smiley base. The bitter end is looped so it can be placed over the antenna tip when not in use. This MOD is compatible with your antenna and can be left on during travel and used when required, so you do not have to keep switching the base. The silicon jacket has superior flex, durability and cold weather performance compared to normal PVC coated wire. And more importantly, it is an insulation material that keeps the capacitive losses to the system at a minimum. Instead of being clamped to the outer collar of the SMA connector on your HT antenna, ours are soldered to prevent attenuation and loss introduced by a clip and acts as a counterpoise so that RF from the HT doesn’t couple with your body. We make 2M Tiger Tails suitable for use with our rubber ducks and they are highly recommended for use where you need maximum range from your antenna. Our Rat weighs 12 grams, and is compatible with all the antennas, so it can be used with any of them. For a mere $19.95, this is a 'must have' for backcountry travel, and a mandatory piece of kit if you are a guide or may be the one that has to summon assistance via radio.
* NEC, the famous computer program for modelling antennas, indicates that 1/4-wavelength is an optimal radiator length for antennas with a vertical radiating element longer than 1/4 wave. The further above the ground the radiator gets, the shorter it can be, but at approx 1M where a Rat Tail may be held in position by the operator of the HT, peak radiation efficiency is going to be close to .25 of a wavelength. Therefore our VHF Rat Tails are about 50 cm long to extend the virtual ground plane footprint to match the goalposts defined by a virtual 2M matrix.
Put another way: this is a much cheaper solution than running a wire along the top of your skis and gluing a TNC Bulkhead to your ski tip so that you can turn your ski into the ground plane!
Rat Tail coiled around antenna for transport.
These "rat tails" are directional and can be used to change both radiation angle and direction**. You'll remember that a 5/8 wave flattens out and goes the distance more than the stock 1/4 wave duck that comes with HT radios. So the Rat Tail gives best performance when pointed in the general direction of the station you are trying to hit (such as a repeater), and right at the virtual horizon, while maintaining a 90 degree angle between the rubber duck and rat tail. It is always best to keep your radio as far away from your body as possible when transmitting, that's where a speaker Mic comes in handy.
- Remove your antenna from the radio.
- Unscrew the SMA knurled base from the bottom of your antenna.
- Screw the rat tail in the same place.
- Re-install your antenna.
- When transmitting, the looped end of the rat tail is the furthest away from your body pointing in the direction of the object you are trying to talk to (an upturned ski pole affords a handy tip to place the loop over if you need to free a hand).
- For travel convenience, you can loop the rat tail around your antenna rather than having to change bases all the time. You can transmit without taking it off while it is coiled, but to get the best performance, deploy it when possible.
- **In marginal conditions, extending the counterpoise horizontally and pointing your hand to steer the radiation pattern where you need it, produces a dramatically stronger signal than letting it "droop" towards the ground. Experiment with the angle of the counterpoise to get the best results. In effect, you are creating a form of "V" type center fed vertical dipole with a bit of gain compared to just the factory installed antenna.