Audioclinic (Q and A) (Jun. 1972)

Boosters and Weak Signal Reception

Q. I noticed your column in the October, 1971 issue of AUDIO. I am wondering about your statement that weak signal reception will be decreased with the use of an Al booster. I have been using one or another of these boosters for years. I regularly listen to stations as far as 200 to 300 miles away, weather conditions permitting. Everything I read indicates that this is not supposed to be possible; FM is supposed to be limited to a distance of 50 or 60 miles.

Is it possible that conditions are so much different out here from what they are in the East, where most of the testing, etc., is carried on that reception over greater distance is possible? Is it possible that the boosters have not been helping as much as I thought? Note that in western Kansas there is no problem from overloading by strong stations. We strain for every tenth of a microvolt we can get.

-John F. Wieland, Liberal, Kansas

A. A booster, used with a tuner of modern design, may degrade reception rather than improve it by adding more noise than signal.

Have you tried listening with the booster disconnected? You may find an improvement. If your tuner is a tube unit or one of the early solid state units, the booster may then be a decided improvement.

With the booster disconnected, signal strength will be less, but if the noise is still less, reception will be improved.

Do not judge reception merely by readings on the signal strength meter.

Listen to stereo signals when making your observations.

When we talk of FM reception being limited to line of sight, we mean normal, reliable reception. Weather conditions, especially temperature inversions, can and do play an important role in bending VHF signals, causing them to stay close to the ground rather than going out into space as they would normally tend to do. It is definitely possible and in fact likely for you to pick up signals from 200 to 300 miles away, assuming that there are few obstructions between your receiver and the source of the signal. This is probably the case in your part of the country.

Changes in atmospheric density can also result in signal bending, or refraction. (Actually, a temperature inversion is just one manifestation of such changes in atmospheric density.) Assuming that your present antenna is the best possible, obtain another one and stack it. This will produce a three dB increase in wanted signal, plus added rejection of unwanted signals and external noise. By adding two more antennas, making a total of four, an additional three dB improvement will result.

Information for vertical and horizontal stacking is probably available from the manufacturer of your antenna. If not, you can find the information you need by writing to the American Radio Relay League, Newington, Conn. 06111.

Triac Power Handling Capacity

Q. My question concerns the use of triacs, specifically the RCA 40526 and 40527. According to the RCA transistor manual, they are identical in every respect except the off-set voltage. The 40526 is rated at 2.5 A with an off-set voltage of 200 V. The 40527 is rated at 2.5 A with an off-set voltage of 400 V. I know that the 40526 can be used at 120 V at 2.5 A for a total power of 300 W. The 40527 can be used at 240 V at 2.5 A for 600 W. It seems to follow that I can use the 40527 at 120V at 5A and have 600 W of power available through the device. Is this correct?

-W. B. Voosen, San Diego, Calif.

A. You cannot use the 40527 rated for 240V operation, run it on 120V, and expect to be able to draw twice the current. Triacs have maximum current rating which must not be exceeded regardless of the voltage applied to the device. It is the current and its resulting internal voltage drop which causes some heating within the triac. The operating temperature must be kept below its design limits. In your application, therefore, if you need a triac which can handle 5 amperes, be sure that its current-carrying capacity is at least this value or you will lose the device in short order.

(Audio magazine, Jun. 1972, Joseph Giovanelli)

= = = =