The New Six Meter Repeater Built by Mike Martell

Transcription

1 June 2001 The New Six Meter Repeater Built by Mike Martell The Repeater That Mike Built By Randy Gudeahn, N1PTB - Editor This is the new 6-meter repeater that is a joint effort between Mike Martell (N1HFX) and the SCRAMS club to generate great enthusiasm in 6-meters. These photos were taken at my QTH when Mike came over to make the final adjustments as I was transmitting off my HF rig. Once the basic adjustments were made, we called Dave, WA1IKN in Gales Ferry to make some low power transmissions. Congratulations to Mike for his expertise in building this fine repeater! H IGHLIGHTS INSIDE THIS ISSUE 1 Six Meter Repeater 2 Field Day and Red Cross News 3-4 Using Transistors as Switches 5 Classifieds, Contacts and Important News 6 Advertisements The RASON Monitor 1

2 FIELD DAY 2001 RASON will have its field day on Saturday, June 23 to Sunday June 24 at the CCC Youth Area of Pachaug State Forest in Voluntown, Connecticut. We will also have the traditional hamburger and hotdog barbecue at 6:00 PM. Your Chef will be Mike Martell. Looking for help with setup, operating, eating and clean up. If interested, please contact Mike Martell, N1HFX at ARC/EX 2001 American Red Cross South Eastern Connecticut Chapter Three Chapters of the American Red Cross in Connecticut are participating in a drill called ARC/EX 2001 on November 30th and December 1st This drill includes a 24 hour period beginning at 6:00 PM on Friday November 30, 2001 and ends at 6:00 PM Saturday December 1, During this 24 hour period The ARC EOC will be opening along with (2) shelters. Now the catch... The Red Cross is seeking help from the three local radio clubs and area amateurs to support this important exercise. We are looking for amateurs to participate during this 24 hour exercise to be stationed at the EOC or at the shelters to support Red Cross Operations. Contact Bruce Adams, KA1ZM at Using Transistors As Switches By Mike Martell N1HFX While transistors have many uses, one of the less known uses by amateurs is the ability for bipolar transistors to turn things on and off. While there are limitations as to what we can switch on and off, transistor switches offer lower cost and substantial reliability over conventional mechanical relays. In this article, we will review the basic principles for transistor switches using common bipolar transistors. The most commonly used transistor switch is the PNP variety shown in Figure 1. The secret to making a transistor switch work properly is to get the transistor in a saturation state. For this to happen we need to know the maximum load current for the device to be turned on and the minimum HFE of the transistor. For example, if we have a load that requires 100MA of current and a transistor with a minimum HFE of 100, we can then calculate the minimum base current required to saturate the transistor as follows: Minimum base current = 100 MA / 100 Minimum base current = 1 MA The RASON Monitor 2

3 In actual practice, it is best to calculate about 30% more current than we will need to guarantee our transistor switch is always saturated. In this case, we will use 1.3 MA. We must also select our supply voltage, so for this example we will use 12 volts. We can now calculate resistor R1 in the circuit as follows: Minimum HFE = 100 Maximum Current Required = 100MA Supply Voltage = 12 Volts R1 = Supply Voltage / ( Maximum Current Required / Minimum HFE * 1.3 ) R1 = 12 / (.1 / 100 * 1.3) R1 = or 10K for nearest standard value. Resistor R2 is not essential to this circuit but is generally used for stability and to insure that the transistor switch is completely turned off. This resistor insures that the base of the transistor does not go slightly negative which would cause a very small amount of collector current to flow. The value of this resistor is not critical but a value about 10 times R1 is normally chosen. For this circuit we will calculate R2 to be 10 times R1 as follows: R2 = 10 * R2 = 100K To turn on our transistor switch all that is needed is to short resistor R1 to the negative ground. While PNP transistors are normally used for a negative ground configuration, it is possible use a NPN transistor if a positive ground configuration is desired as indicated in Figure 2. The calculation of resistor values is identical to the PNP version. However, in the NPN transistor, R1 must be shorted to the positive end of the supply to turn the switch on. While our transistor switch can easily replace many mechanical relays, it does have a few drawbacks. The maximum design current must not be exceeded or the output voltage will be reduced. A short circuit of the output will overheat and destroy the transistor in many cases. Although the transistor is in saturation when turned on, about.3 volts is lost through the collector to the emitter of the transistor. We must also insure that the maximum power dissipation of the transistor is not exceeded. We can calculate the power dissipation by multiplying the current by.3 volts. In the case of 100 MA, the transistor must be able to withstand 30 milliwatts (.3 times.1). The RASON Monitor 3

4 Transistor switches are used for a wide variety of applications. Many amateurs will notice that the circuit in Figure 1 is used as the PTT in many transmitter circuits. Transistor switches are commonly used to turn on transmitter circuits, LED s, cooling fans and even relays. However, when using a transistor to turn on a relay coil, it is very important to use a 1N4001 diode reversed biased in parallel with the relay coil as in Figure 3. This is to prevent the kickback voltage in the reverse polarity from destroying the transistor. This reverse voltage occurs momentarily when the normal current stops flowing through the coil. It is good practice to always use a diode when turning on any inductive load. Transistor switches are often used to take the low-level output from logic circuits to turn on or turn off a particular device. The actual transistor used as a switch is not critical in these applications. Virtually any general purpose NPN or PNP transistor can be used as a switch. All that is needed is to know the minimum HFE and the power dissipation of the transistor. While most all transistors in a TO-92 case will have HFE s of at least 100, many power transistors in TO-220 cases often have an HFE no greater than 25. It is essential to know the HFE or Beta of a transistor, so that we can have a large enough base current to achieve saturation. If a power transistor is used to turn on a high current device, it may be necessary to use another lower current transistor switch to drive a transistor switch used in a high current application. This is especially important when using a low current logic output from a CMOS IC. While there are a few applications where our transistor switches may not be suitable, it is usually a much more reliable and inexpensive alternative to using mechanical relays. These circuits are low in cost and offer ease of design for the radio amateur. 73, N1HFX Eastern Connecticut Traffic Net (ECTN) Needs You! As of late, there has been very little participation in your local Traffic Net (ECTN). Please use this net for what it is designed for, SENDING TRAFFIC or PRACTICE. The net meets every night at 9:00pm on the RASON repeaters, and Why not send a message to a relative, friend, or your fellow ham? It doesn t take much to send a message, if you have never sent one, we will show you how to on the net. Try being a Net Control, we are always looking for new NCS s to fill in or take Friday night, which is open at this time. I can t stress this enough, this net is here to provide training in traffic handling in the event of a disaster where all other means of communication are disabled. Support your local Traffic Net, it only takes a few minutes out of your busy day! 73, Randy, N1PTB The RASON Monitor 4

5 C ALENDAR OF E VENTS?? THE NEXT RASON MEETING WILL BE HELD ON JUNE 20 TH AT 7:30 P.M. AT THE NORWICHTOWN MALL COMMUNITY ROOM. ALL MEMBERS AND FUTURE MEMBERS ARE ENCOURAGED TO ATTEND. SHARE THE HOBBY WITH A FRIEND AND BRING THEM ALONG TO SEE WHAT WE RE ABOUT. TALK-INS WILL BE PROVIDED BEFORE THE MEETING ON THE AND REPEATER.?? FIELD DAY WILL BE HELD JUNE 23 AND JUNE 24 TH AT THE CCC YOUTH AREA OF THE PACHAUG STATE FOREST IN VOLUNTOWN. REFER TO ARTICLE IN NEWSLETTER FOR DETAILS. Area NETS?? HORIZONTAL ENGINEERS Nightly at 7:00 p.m. on ?? AREA 4 ARES NET Every Monday Night at 8:00 p.m. on ?? AREA 4 Weather NET Every Wednesday Night at 8:00 on (PL 156.7)?? E.C.T.N. Nightly at 9:00 p.m. on and ?? RASON Phone NET Every Thursday Night at 8:00 p.m. on (+ -)?? CONNECTICUT Phone NET Mon.- Sat at 6:00 p.m. on (+ -) and Sunday at 10:00 a.m.?? THE WEATHER NET will meet on on the First Wednesday of each Month, at 8:00 p.m.?? T.I.P.S. NET Every Tuesday at 7:30 on (PL 156.7) RASON CONTACTS President: Mark Noe, KE1IU Vice President: Bruce Adams, KA1ZMZ RASON Monitor Editor: Randy C. Gudeahn, N1PTB P.O Box 161 Taftville, CT n1ptb@arrl.net RASON Monitor Publisher: Mike Martell, N1HFX Classifieds There are no items reported for sale this month. * * *IMPORTANT NOTICE * * * VEOSEC CONNECTICUT CO-CHAIRMEN Michael J. Martell, N1HFX Roy Hilt, K1JNR 74 Lillibridge Road 41 Jerome Road Plainfield, CT Uncasville, CT VEOSEC AMATEUR RADIO LICENSE EXAMINATIONS AUGUST 18, 2001 NOVEMBER 17, 2001 See January 2001 RASON Monitor for details. The RASON Monitor 5

6 Call Lentini s at or The RASON Monitor 6