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"Skip” propagation was minimized by what we now call “NVIS” – low “cloud burner” antennas that were effective at shorter distances (<100 miles). Infantry man-packs, walkie talkies, and vehicular radios, such as in scout cars, would typically use 2-9 MHz range frequencies (which is why many BC-611s were crystalled for 3885!). So, these were the frequency ranges the S.I.A.M. units would monitor, and they were issued BC-342 receivers for this purpose.
With two RF stages, the BC-342 had plenty of sensitivity when used with short non-resonant antennas. This was a plus since S.I.A.M. required the ability to monitor whatever range of frequencies was in use.
They also had a complete inverted-L antenna system as part of the SCR-188 radio set. This would have been set up for transmitting reports to “higher ups” but could have also been pressed into service for monitoring. However, as the Technical Manual says, “No prepared antenna is provided for this radio set for attachment to the receiver antenna post. It is intended that about 50 ft. of insulated wire W-29, furnished with the set, be attached to the antenna binding posts and the far end flung over a tree or other convenient support”. So, there’s little doubt that the S.I.A.M. unit used random wires for monitoring antennas as well.
No information can be found about the AN-24-A “flat top antenna” listed on one manifest. It sounds similar to the SCR-188 antenna, and if so, it could have been configured for use from 1.5 to 12.5 MHz, which would certainly have covered all the frequencies of interest.
With two RF stages, the BC-342 had plenty of sensitivity when used with short non-resonant antennas. This was a plus since S.I.A.M. required the ability to monitor whatever range of frequencies was in use.
They also had a complete inverted-L antenna system as part of the SCR-188 radio set. This would have been set up for transmitting reports to “higher ups” but could have also been pressed into service for monitoring. However, as the Technical Manual says, “No prepared antenna is provided for this radio set for attachment to the receiver antenna post. It is intended that about 50 ft. of insulated wire W-29, furnished with the set, be attached to the antenna binding posts and the far end flung over a tree or other convenient support”. So, there’s little doubt that the S.I.A.M. unit used random wires for monitoring antennas as well.
No information can be found about the AN-24-A “flat top antenna” listed on one manifest. It sounds similar to the SCR-188 antenna, and if so, it could have been configured for use from 1.5 to 12.5 MHz, which would certainly have covered all the frequencies of interest.
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