Thread: Rca ant751
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Old 20-May-2017, 7:30 PM   #42
Retired A/V Tech
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,543
The tests that I have made so far tell how well the antennas work indoors with my signals, but I have been searching for a test method that would give a more accurate indication of relative antenna gain.

I have settled on an Antennas Direct DB2E antenna and a Blonder Tongue HAVM-1UA Frequency Agile Modulator for a stable transmitted test signal.

I read about the antenna test measurements done by Kent Britain (WA5VJB). He has made measurements with the test antennas at ground level and above ground level. When the antennas are elevated, the receiving antenna picks up the direct signal and a signal reflected from the ground. I tried it both ways. The ground level signals level are much weaker, but the gain difference between antennas is about the same, so I used elevated antenna measurements. Kent was making measurements at microwave frequencies with horn antennas, see p. 5:

First I did a comparison between the antennas elevated on tables and on the floor. The HAVM is only for UHF:

Comparison between antennas on tables and antennas 
on the floor for gain comparison measurements.

                 TABLES                  FLOOR

Channel    GE PRO    GE Attic     GE PRO    GE Attic
            29884     34792        29884     34792
            dBmV      dBmV         dBmV      dBmV

15         -11.1     -13.4        -20.3      -22.3
28         -10.0      -9.8        -24.9      -23.4
39         -12.1     -12.7        -23.5      -24.2
Attached Images
File Type: jpg DB2EandHAVM.jpg (171.0 KB, 2889 views)
File Type: jpg RCAANT7511rcvHAVM.jpg (147.0 KB, 2972 views)
If you can not measure it, you can not improve it.
Lord Kelvin, 1883

Last edited by rabbit73; 20-May-2017 at 8:14 PM.
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