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nuckolls.bob(at)aeroelect
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 Posted: Sat Jul 18, 2020 6:09 am Post subject: IS a COM ANTENNA GROUND PLANE NECESSARY |
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At 12:17 AM 7/18/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: James Kale <jimkale(at)roadrunner.com>
At 3.8 SWR the transmitter is in danger of over heating to the point of meltdown!!!!! |
This used to be the case back in the day. During the
vacuum tube era, transmitters were a bit more tolerant
of high swr especially given that two-way radio communications
were very low duty cycle. Except for when you're reading
your flight plan to the FSS, transmissions seldom lasted
more than a few seconds.
Early solid state radios were a bit more fragile
given their thermal weak-spots in tiny junctions
within the transistor's architecture . . . but even
that vulnerability faded with improvements in
transistor design. Further, it is not uncommon
these days for a transmitter to have an SWR
bridge BUILT IN to the antenna output pathway
with REVERSE power signals looped back to the
transmitter's power amplifier such that operating
power is scaled down in response to high SWR.
The most probable manifestations of the
high swr . . . especially in a low conductivity
airframe are (1) poor operational performance
and (2) high levels of radio frequency energy
in the cockpit during transmissions. This
phenomenon has been observed countless times
in OBAM aviation's 'plastic' airplanes.
In the case before us, the coax is poorly
terminated thus making the whole feedline
a radiator of energy along it's entire
length . . . which puts significant energy
into the aircraft interior.
RF interference with cockpit instrumentation
is most often observed with products not designed
with rudimentary DO160 qualification guidelines
in mind.
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Sat Jul 18, 2020 6:11 am Post subject: IS a COM ANTENNA GROUND PLANE NECESSARY |
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At 07:54 PM 7/17/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>
I took my SWR meter to the airport today and checked my friend's com antenna. The SWR was 3.8
Now he knows that his antenna installation will not work very well.
He is considering mounting a new antenna on top of the fuselage. |
Sounds like a plan . . . thanks for helping
this builder out -AND- sharing the experience
here on the LIST.
Bob . . .
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