I'm rigging an old Lowrance LFG300 flasher to use in a pedal boat (I know,
I'm nuts) that's to be used on a small residential lake. I would like to
shorten the cable to about 6 or 8 ft. Will this have any or much effect on
the unit? I'm only interested in checking depth of lake as it's been years
since the lake was dredged.

Also, does turning this unit on with out the transponder connected do any
harm to this unit.

Rob Mills ~ Tulsa

"Rob Mills" wrote in message
news:7NSYc.9395$gl.6387@okepread07...
I'm rigging an old Lowrance LFG300 flasher to use in a pedal boat (I know,
I'm nuts) that's to be used on a small residential lake. I would like to
shorten the cable to about 6 or 8 ft. Will this have any or much effect on
the unit? I'm only interested in checking depth of lake as it's been years
since the lake was dredged.

Theoretically yes but not enough to notice.


Also, does turning this unit on with out the transponder connected do any
harm to this unit?

Dunno but might ruin it so I wouldn't.

"Vito" wrote in message
...


Theoretically yes but not enough to notice.


That's what I was hoping. Thanks, RM~

The cable should not be shortened at least that is what I was told. It
does not harm the unit to turn it on with out the transducer being
connected.

Rick

Rob Mills wrote:
I'm rigging an old Lowrance LFG300 flasher to use in a pedal boat (I know,
I'm nuts) that's to be used on a small residential lake. I would like to
shorten the cable to about 6 or 8 ft. Will this have any or much effect on
the unit? I'm only interested in checking depth of lake as it's been years
since the lake was dredged.

Also, does turning this unit on with out the transponder connected do any
harm to this unit.

Rob Mills ~ Tulsa

"Rick" wrote in message
...
The cable should not be shortened at least that is what I was told. It
does not harm the unit to turn it on with out the transducer being
connected.

The transmitter sends a pulse of electromagnetic energy down the coax to the
transducer at the speed of light. The transducer converts that to sound
which travels at (yup) the speed of sound in water; then it listens for
echos and converts them back to electromagnetic signals sent via the same
cable to the receiver. The receiver measures the total time required by all
this to determine depth. If you cut 10' off the cable that determination
will be off by 2x the time required for a speed of light signal to do that
10'. Since the speed of light (186,000 miles PS IIRC) vs sound (about 1100
feet PS) that error is small.

"Vito" wrote in message
...

"Rick" wrote in message
...
The cable should not be shortened at least that is what I was told. It
does not harm the unit to turn it on with out the transducer being
connected.

The transmitter sends a pulse of electromagnetic energy down the coax to
the
transducer at the speed of light. The transducer converts that to sound
which travels at (yup) the speed of sound in water; then it listens for
echos and converts them back to electromagnetic signals sent via the same
cable to the receiver. The receiver measures the total time required by
all
this to determine depth. If you cut 10' off the cable that determination
will be off by 2x the time required for a speed of light signal to do that
10'. Since the speed of light (186,000 miles PS IIRC) vs sound (about
1100
feet PS) that error is small.

It's not the cable delay that counts in this case. The cable capacity is
important here and is used as part of the tuned circuit that drives the
transducer. If you change the cable length, you change the capacity of the
cable and therefore the resonance frequency of the tuned circuit. The result
is that the sounder cannot generate a sufficient high voltage to drive the
transducer.

Meindert

In article ,
"Meindert Sprang" wrote:

It's not the cable delay that counts in this case. The cable capacity is
important here and is used as part of the tuned circuit that drives the
transducer. If you change the cable length, you change the capacity of the
cable and therefore the resonance frequency of the tuned circuit. The result
is that the sounder cannot generate a sufficient high voltage to drive the
transducer.

Meindert

I hate to rain on your parade here Meindert, but most, if not all,
consumer Marine Depth Sounders, have Transformer Coupled outputs that
are resonate in and of themselves, and really don't care what is
connected to their output link as long as it isn't shorted.
The transducer is a Barium Titante Crystal that looks like a
capacitive load to the sounder transmitter, and if it isn't actually
connected, the few watts of transmitter power is just burned up in the
transformer as heat, as the average power is very low, similar to a
radars average power compared to it's Peak Power. Now if we are
talking commercial Depth Sounders, we are talking a horse of a bit
different color, but again operating them into an open transducer
line isn't very likely to cause any problems with the transmitter,
you just don't get any return. The result of all the above is that,
one "could" actually go and tune the transmitter for the best coupling
to the transducer connected, but the gain in signal/noise by doing so
isn't really significant. (Like less than 2db or so) The length of the
transducer cable isn't critical to the operation of the souder, and
many of these installations in the North Pacific Fleet have splices
in them due the cost of hauling the vessel to change transducers,
compared with just connecting a new sounder to what is already in the
hull. (Frequencys all being the same, between the old and new units)
There is Theory, and then there is 30 years of Practical........

Bruce in alaska
--
add a 2 before @

"Bruce in Alaska" wrote in message news:bruceg-
I hate to rain on your parade here Meindert, but most, if not all,
consumer Marine Depth Sounders, have Transformer Coupled outputs that
are resonate in and of themselves, and really don't care what is
connected to their output link as long as it isn't shorted.

That is technically impossible. And you as a radio man should know this.
Just like it is impossible to create a fixed antenna tuner that matches
anything between a screwdriver and a full size dipole, without changing a
tuning element.

Please read http://www.airmar.com/pdfs/technical/sensor.pdf. Specifically,
at page 21, right column, last bullet, it says that if the cable must be
extended, it requires removal of capacitance in the tuning circuit. So if
you short a cable, adding capacity is required.
In the example at the next page, a calculated capacitance of 2428 pF s shown
for the crystal. To get the example resonating, the calculations show that
6776 pF is to be added for proper operation.
Now, if you would cut a 10 meter cable in half, you remove 500pF from the
equasion, which will have significant influence on the proper operation.

Meindert