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BOAT/US did a report on Marine VHF radios last year, and it was prety
conclusive that the inexpesive radios have all the functionality of the
higher priced radios. You can get a pretty decent VHF with "no frills"
for about $150 here in the US (at discount stores or through catalogs).
I agree with the previous note that what is wrong is in the final
amplifier stage. Most probably you fried the output transistor (very
typical in transmitting without a load).
Marine electronics have dropped dramatically inprice over the last
few years- If the radio is over 5 yrs old, I would be tempted to simply
replace it (unlkess you have a freind who is liscenced and can make the
repair).
If it is the final output stage ( I would bet on it), all it usaully
is is soldering in a single transistor and checking the frequencies- a
quick job. If it is not that, I would scrap it and buy a new radio,
probbaly at only little more than the repairs would cost.
Dick
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| One last possibility before you purchase a new radio: it may be that
there is a short in the combination of the coax line or the connector.
This is the most unreliable part of these systems. The amplifiers have
reflected power detectors in them that will power down the stage if
there is a short present. This ought to function properly for
short-duration transmissions, and even for long transmissions. So it
is possible that with the short your amplifier stage may still be good.
One way to check this is by seeing if it works with a completely
different transmission line and antenna. (Many offshore boats carry
such a spare antenna.)
A second way is to use a standing wave meter to measure the ratio
between reflected and forward power. If you have high reflected power,
then it is likely that the transmission line is shorted or open.
Corrosion in the line can cause intermediately bad situation that would
allow you to still hear stations, but have too high a SWR (standing
wave ratio) to transmit.
Marine electronics dealers and many ham radio operators will have one of
these. I have one that you could borrow if you could get it back
within a week or so. I live in Winchester, and work at MLO.
/Don (dtn: 223-5956)
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| On the prop shaft issue- first I assume you are sure it sheared off and
not simply pulled out of the coupling? Doyou see a small stub sticking
out of the coupling?
Indeed, such shear could be caused by a misalignment. Stainless does
have some rather bad work hardening properties, so a minor flex could
have hardened the shaft enough to cause it to break. A too hard piece
of steel will break just like glass- makes about the same sound when it
breaks, and leaves a sharp, clean line.
The solution of course is to properly align the shaft and engine. And
to check it from time to time to be sure it doesnt shift. ALigning an
engine is VERY tedious. The basic process is to put the shaft in place,
slip the coupling up until the two faces are just a few thousands
apart. You then test, with a feeler gauge, at several points around the
gap. The trick is to shift the engine side to side or up and down until
the gap is EXACTLY the same all around. It takes a rather delicate feel
of the gauge to tell if its to tight in one spot.
Also note, most couplings have a spigot in the center, which will pull
the two faces into some alignment, with a slight flex to the shaft. You
then think you have proper alignemnt, but have a buit in stress- this
is quite likely what caused the damage in this case.
Lots of book show pictures of the alignment process, but of course they
ignore the problem that to even SEE the coupling you are likely
standing on your head, hanging down thru some locker, with oil and
bilge slime dripping off your nose. Its little wonder few shafts are
properly aligned.
This could lead into a discussion of using a flex joint of some kind in
the shaft. This is rarely done, although Im not sure why. It does raise
some interesting issues of vibration and is generally harder to
engineer that a rigid joint. Im using a flex joint on my steam boat.
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| I am afraid that it was a shear, not the shaft pulled out.
Your comment about steel being like glass is interesting though, as the
sheared face does have the look of a piece of broken glass sort of
clean but if you look closely you can see unevenness.
My guess is that it has to be due to misalignment, perhaps the engine
settled over time.
I guess that I should start a note now on techniques for sailing in and
out of moorings ?
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