Friday, March 16, 2018

Update on the Godar FM DXR 1000 antenna

Extended full length, the antenna has a high SWR at FM radio frequencies.  The manufacturer recommends extending full length for AM and TV frequencies, this has the effect of suppressing FM broadcast stations, which is useful because they are quite strong and can interfere with AM and TV.

The manufacturer suggests reducing length by 5 inches for FM if it needs it.  This creates excellent SWR at FM broadcast frequencies, so I'd suggest always doing this for FM.  I measured the precise length of the second section required for best FM performance: 3 inches.  All other sections are fully extended.

I couldn't see any effect of this change above 120 Mhz, so I left it that way--optimized for FM, though I "intend" to use this antenna for a 140 + 880 Mhz scanner, it might also serve as an extra FM antenna.

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