By John Doty, rec.radio.shortwave, 5 Sept 1994
The key to minimizing noise pickup with an end fed antenna (Beverage, longwire, inverted L, or vertical) is to feed it with coaxial cable whose shield is well grounded. Unfortunately, coaxial cable is a poor impedance match to a wire antenna, except perhaps at a few special "resonant" frequencies. A matching transformer at the base of the antenna can smooth out the fluctuations in antenna system efficiency with frequency, yielding an antenna system that works well enough for good reception from longwave to the top of the shortwave range.
I've posted instructions for winding such a transformer several times on rec.radio.shortwave. My homebuilt transformer works well. However, after about the fifth time this summer that I left the antenna cable plugged into my receiver by accident, I decided I needed to improve my lightning protection to minimize the chance of damage. After looking through catalogs, I decided to buy a matching transformer with internal lightning protection.
The 180 is *very* solidly built. A barrier terminal strip is provided for three different antenna inputs, allowing impedance transformation ratios of 6:1, 9:1, and 12:1 to be chosen. These are labelled as 300, 450, and 600 ohms for use with 50 ohm cable. A "UHF" type coax connector is provided, along with a nice grounding stud for grounding the case.
The unit appears to be hand made. The transformer itself is wound on a two hole "balun core". There's a gas discharge tube across the transformer secondary and a 3 kV capacitor between the secondary and the central socket of the coaxial connector. The workmanship is excellent.
The shunt inductance of the transformer drains static to ground. The discharge tube clamps the voltage due to a sudden discharge. Most of the energy in an electrostatic discharge is at low frequency and below: the capacitor blocks this. This is worthwhile protection, but not comprehensive enough to completely protect a sensitive receiver: more protection is needed at the receiver end of the cable. This is not a criticism: I don't believe that comprehensive protection is possible in a single package.
The unit is rated for use at frequencies of 1-30 MHz with 50 ohm cable. I use 75 ohm cable in my system: this might be expected to reduce the frequency range slightly. To check it, I used the transmitter for a radio controlled boat (at 27.145 MHz) and a local radio station (at 1.600 Mhz) as stable (ground wave) reference signals. I compared the 180, using its 9:1 input, with my homemade 9:1 transformer using the S meter on my Drake R8. The antenna was a 17 m inverted L. At 27.145 MHz, there was no detectable difference (<1dB) between the two units. At 1.600 MHz, my homebuilt transformer yielded a slightly stronger signal (1-2 dB). Nevertheless, the Model 180 has enough low frequency response that I can easily hear the antenna's noise floor all the way down to 100 kHz, so a "better" response would not, in fact, improve my listening.
In short, I cannot find any fault in this unit. At $32 it is also the least expensive transformer of this type that I'm aware of (unless you make your own). ICE takes orders at 1-800-423-2666. I have no connection with ICE except that I'm a satisfied customer.
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