Last night inadvertently I left my multi-mode beacon (blogs passim) running into the g5rv - but with my MFJ 969 tuner in BYPASS Mode. The results were surprising - in fact, I think I have achieved significantly better dx than with the antenna "tuned".
Here's a map of spots over the past 24 hours...
The beacon is regularly spotted in North America, but this performance exceeds anything seen before - and the spot by Jay, w5olf in Colorado (not so far from my old home in WY) is the best dx (4537.4 miles) the beacon has achieved to date. This transatlantic spot and others into Florida and Maine were achieved this morning, continuing the recent trend for improved day-time dx. All this with the antenna de-tuned...
Here's the indicated SWR (as measured by sending a CW tone from the FT817 into the system - the beacon barely moves the needles of the meter) with the tuner active...
Here's the SWR with the tuner in BYPASS...
What's going on?
It appears that either i) there are losses in the tuner in "TUNED" mode that exceed the benefits of tuning or ii) the source impedance of the beacon is very different from 50 Ohms (the final stage is a low-pass filter, designed from standard methods assuming 50 Ohm operating impedance).
Perhaps you can suggest another explanation?
In the meantime, I guess I'll keep running the beacon into the UNTUNED g5rv !
...-.- de m0xpd
Perhaps you can suggest another explanation?
In the meantime, I guess I'll keep running the beacon into the UNTUNED g5rv !
...-.- de m0xpd
Tuner losses, where quoted by the manufacturer, are usually between 5 and 10%, but the quoted figures are for when the load is 50 ohms, when you wouldn't need the tuner anyway. I suspect the tuner losses when the mismatch is significant are much higher, and could well end up exceeding the mismatch losses in the feeder. My K2 ATU could get a perfect match on my old attic wire loop even on 80m and 160m where the predicted SWR was astronomical, but I never heard anyone on those bands never mind worked them. So I suspect that these wide range ATUs may end up absorbing most of the power when they show a good match on a non-resonant antenna. It would be an interesting area for someone to investigate. It would help explain why half wave dipoles tend to outperform similar wire antennas that require a tuner.
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