September 18, 2020

Transmitting using a vintage Radio Shack center-loaded telescoping antenna

I have a vintage Radio Shack center-loaded telescoping antenna from the early 1990's.  It has a BNC connector and a loading coil in the middle of the telescoping sections.  It ordinarily sits in a box along with other radio odds and ends that I don't use regularly.  Radio Shack made these for ages and you can still find them for sale online.

Radio Shack center-loaded telescoping antenna with all sections collapsed

I was recently working on a vintage Kenwood TH-22AT 2m HT that still has its original rubber duck antenna.  The antenna wasn't pulling-in stations very well so I decided to dig out my old Radio Shack telescoping antenna and give it a try.  I was happy to find that the Radio Shack antenna worked better than the stock rubber duck.

As I was setting it up, I remembered that some adjustment is required in order to use it for transmitting.  The antenna can be used on a transceiver or a receiver such as a scanner.

Receiving: 25 MHz through 1296 MHz
Transmitting: Can be used as a 1/4 wavelength transmitting antenna from 130 MHz through 535 MHz.
  • Caution
    • When you use the antenna to transmit, you must always collapse the section located just above the loading coil. If you do not collapse this section, you might damage the antenna and your radio.
    • When you use the antenna to transmit, you must calculate the 1/4 wavelength and adjust the antenna length accordingly. If you do not do this, you can damage your transmitting equipment due to an improper standing wave ratio (SWR).
      • Use this formula to calculate the proper length for a 1/4 wavelength transmitting antenna: 2834 / Freq. in MHz = Antenna Length in Inches 
Common 2m Band Antenna Lengths
  • 144.000 Mhz --> 19.7 inches
  • 144.500 Mhz --> 19.6 inches
  • 145.000 Mhz --> 19.5 inches
  • 145.800 Mhz --> 19.4 inches
  • 146.520 Mhz --> 19.3 inches
  • 147.570 Mhz --> 19.2 inches
  • 147.990 Mhz --> 19.1 inches

When receiving only:
  • 25 Mhz to 136 Mhz - Extend all nine sections of the antenna
  • 136 Mhz to 174 Mhz - Extend only the top four sections
  • 174 Mhz to 1296 Mhz - Extend only 1 to 3 lower sections

Good DX and 73, NJ2X

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