David Kinsell wrote:
Eric Greenwell wrote:

David Kinsell wrote:

The FSG 2T very specifically says don't try to transmit with less
than 11 volts, so I think that would be an expensive option that
really wouldn't help out.


Contrary to what Dave writes, here is what the FSG 2T operation
manual says on page 50 of the FSG 2T Installation and Operation
manual, available on Wings&Wheels or Dittel's web site:

6.13 Emegency Operation

Without degradation the FSG 2T can be operated on a dc source
between
11 Vdc and nearly 9 volts. This however will NOT reduce the TX output
level, RX sensitivity, and audio output power, due to internal supply
regulation. Below 11 volts the dc indicator flashes continuously as
low supply warning. Since the current drawn from the battery will
increase with lowered Dc supply voltage, the automatic shut-down will
speed-up.

If the supply voltage drops below 9 Vdc the FSG 2T swithces OFF
itself. This automatic feature avoids battery damage due to deep
discharging, even if the radio is left switched ON for months! This
is true for all types of 12 Vdc batteries.

If the battery recovers and voltage exceeds approximately 10.5 Vdc,
the radio returns to operation with the last used setting.



Utter baloney. The brochure for the radio, also available at the W&W
site, says:

"Is onboard supply sufficient? Observe onboard supply indicator
particularly during transmit, at least 11.0 Vdc must be shown!"

http://www.wingsandwheels.com/FSG2T%20Brouchure.pdf

Interested pilots should read the rest of the brochure. What Dave is
referring to is the section that begins:

"Function Checks:
If the Transceiver FSG 2T does not operate correctly, check the following:"

This is a trouble shooting section, not a normal operation section.
Making sure the pilot is using a battery with sufficient charge to test
the radio is very sensible, and a battery with less than 11 volt under
load is nearly exhausted, or there is a high resistance in the wiring or
the battery.

The Technical Data section of this brochure includes the specification:

"RF Output: = 5W into 50 ohms (carrier power), = 18 W (PEP) @ 9 to 16
VDC."

This is the same as the manual. I don't see how it can be stated any
more clearly that this radio will function at full power down to 9
volts. It does not mean your radio will be able to transmit with a 12
volt battery that only has 9 volts left on it. The FSG 2T manual makes
this clear, and has a table with estimated times of operation as your
battery discharges below 11 volts. How low the battery voltage can go
and still allow you to transmit depends very much on the size and
condition of your battery.

Question: Why do Dittel, Becker, and Filser have such broad input
operating voltage ranges?

Answer: "These voltages ranges are a European requirement" - Eric
Pscherer, Dittel engineer, in a recent phone call to me. Further, he
stated the new requirement is now 9.1 volts to 16.1 volts, and that
these ranges are easy to achieve with the power supplies now available.
In the past, he said, switching supplies were too noisy (electrically)
to use in receivers, but that is not the case now.

Question: What are the European requirements?

Answer: The requirements for voltage range and many others parameters
are contained in the RTCA/DO-160E document, "Environmental Conditions
and Test Procedures for Airborne Equipment", published by RTCA, Inc., in
Washington, DC. Anoraks will want to peruse this large (778 page, 20 MB
pdf file!) and mind-numbing document, a 2004 draft of which may be
downloaded here (found by Tom Seim):

http://pr.erau.edu/~lyallj/SC135/D-to-E.pdf

or you can purchase a copy of the current document from RTCA for a few
hundred dollars. Incidentally, the document covers far more than just
radios.

The voltage range section for Category B, which our radios fit into, is
in 16.6.1 (Normal Range), and a few pages down you will find the
values for Abnormal Range.

What it means for glider pilots is our European radios are designed to
operate properly on a 12 volt battery, even one that is essentially
exhausted. Motorglider pilots will be delighted to know the standard has
stringent requirements for withstanding voltage surges produced by
engine driven generating systems, and starting their engine with the
radios on (the usual case during an in-air restart, at least for me!) is
very unlikely to cause any damage.

Question: Why the heck does DO-160D ask for such a voltage range when
the radio will be operating on 13.8 volts all the time?

Answer: I can only guess that it is to ensure operation in situations
where the generating system has malfunctioned (alternator gone bad,
drive belt broken, etc) and the battery, or a much smaller backup power
source, has to supply power. Airplane pilots tend to be very dependent
on their radios and other instruments, and someone flying IFR is not
going to be happy if the instrument quits before the battery does.

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA