This evening, with little sign of F2 propagation, I ventured out to test the range of the 10m Tenbox TX as it is currently. For the TX antenna I used the coax up to my 10m halo as a vertical tuned with the Elecraft T1 ATU. At the RX end, in the car, I used the FT817 with a small base loaded mag-mount.
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| Tenbox AM TXing with MP3 callsign message on the PC |
What I should have thought about was the noise on AM from street lights! When the signal is strong in the village this is no issue at all, but traveling to the next village 3km away there were several spots where the buzz from sodium street lights just killed the little signal. Both antennas are compromised, so another 3-6dB of signal level should be possible with a proper 1/2 wave antenna at each end or with a better car antenna.
Maybe this project, although great simple fun, isn't going to quite meet my needs, whereas a DSB transceiver would? Receiving the DSB signal as SSB and the improvement over AM will be around 9dB with better noise immunity. However a simple direct conversion RX would not be suitable to use (easily) with a DSB TX, whereas the AM Tenbox would be fully 2-way compatible with another identical AM unit.
Conclusions so far
(a) 6-10dB more may be needed to meet the design objectives with AM.
(b) It is worth repeating the very same test now using a DSB TX with the same power to compare.
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