[saltysenior]

when hooking up a 12v vhf radio and other electronics , should the inline fuse go on the hot or the ground wire ????

[dennismc]

Man, if you don't know that, maybe you should leave well enough alone, it goes in the hot wire.

[NYCAP123]

Originally Posted by dennismc

Man, if you don't know that, maybe you should leave well enough alone, it goes in the hot wire.

As flip as that sounds he's right. The VHF is no big deal (just be careful with the antenae) so go for it, but "other" electronics can get a bit sensitive and expensive if you do it wrong.

[FISHTIGUA]

Another point about VHF fuses. Why do they fit those cheap and nasty spring-loaded inline fuses?

The first time you open it the bloody spring shoots across the floor, only to be found very early in the morning when barefoot and coffee in hand.

Just cut them out and put a blade type fuse holder in, it saves a lot of swearing.

Fish

[Henning]

Originally Posted by FISHTIGUA

Another point about VHF fuses. Why do they fit those cheap and nasty spring-loaded inline fuses?

Because they're twenty five cents cheaper....

[Marmot]

Originally Posted by NYCAP123

The VHF is no big deal ... so go for it, but "other" electronics can get a bit sensitive and expensive if you do it wrong.

The fuse is there to protect the wiring, not the load so "sensitivity" has nothing to do with it.

[saltysenior]

Originally Posted by Marmot

The fuse is there to protect the wiring, not the load so "sensitivity" has nothing to do with it.

ya mean i'm not real dumb ???

[Marmot]

Originally Posted by saltysenior

ya mean i'm not real dumb ???

Probably not ...

The reason the fuse goes in the hot wire is so that any fault in the load that creates a large current draw will prevent the "hot" wire from becoming really hot and causing a fire. If the fuse was in the ground wire and the fault was a short circuit between an energized part of the radio and its case or other part that shares a common ground for example, the fuse would never open and the radio and or the wiring could easily burn the boat.

The best place for the fuse is at or near the source of power where the supply wire is connected. That way a short anywhere on the wire will cause the fuse to open. If the fuse is right next to the radio and the wire were to chafe and short out somewhere inside the panel, it would still burn.

[saltysenior]

o k we got that straitened out.....now a new question.....way back when, i remember winding copper wire around a long bamboo pole,then varnishing it ,to serve as an antenna for an a m marine radio that was used then...2638 and 2738....the length of the wire was important as i recall......if i was to try to make a similar antenna for a v h f marine radio, appx. what would be the length of wire to be used ????

[Marmot]

Originally Posted by saltysenior

...if i was to try to make a similar antenna for a v h f marine radio, appx. what would be the length of wire to be used ????

Here are the two links you need.

First, determine the frequency for the channel you want to tune for:

http://www.navcen.uscg.gov/marcomms/vhf.htm

Then plug in the information to determine the resonant length of a radiator for that frequency:

http://www.crompton.com/wa3dsp/hamradio/antcalc.html

Personally, I would just buy an antenna.

[saltysenior]

thank you....found out the avg. vhf marine band freq. is 156.75.... the other table shows for that freq. , the antenna should be about 35.8""......sooooo if we were to cut a c.b.antenna whip down to 35.8 "" we would have something thing that would work ????

[Marmot]

Originally Posted by saltysenior

thank you....found out the avg. vhf marine band freq. is 156.75.... the other table shows for that freq. , the antenna should be about 35.8""......sooooo if we were to cut a c.b.antenna whip down to 35.8 "" we would have something thing that would work ????

Most likely, sure. The length you calculated is approximate anyway (as well as being approximately 1/2 wavelength for that frequency) and the diameter of the radiator effects the length as well as the frequency and bandwidth. Antennas are as much an art as science and there are many ways to go to obtain "gain" or increase the "effective radiated power" and angle of radiation.

If you get an old CB antenna that has a fat bit on the bottom, it is probably a loading coil that is tuned for the lower CB frequencies and snipping the upper element might not give you the best match.

Unless you are doing this for fun, why not just buy one? The test equipment needed to determine a good match costs more than a cheap but effective antenna. A bad match will impose more heating loads on the RF amplifier stage and shorten the life of your radio. Those big fins on the back of the radio are there to dissipate the heat produced with a good match. Have fun anyway, it is an interesting subject and can be a fun project.

[saltysenior]

for a safety issue we are going to try to use vhf in our hunting area...[please no preaching].....doing this on a tight budget.....all monies spent on other methods that turned out unsatisfactory .....nowadays boat yards have guard dogs around their dumpsters..

[Marmot]

Originally Posted by saltysenior

for a safety issue we are going to try to use vhf in our hunting area...[please no preaching].....doing this on a tight budget.....all monies spent on other methods that turned out unsatisfactory .....nowadays boat yards have guard dogs around their dumpsters..

What you might want to look into then is a directional antenna that doesn't send the signal out in all directions. That would increase the signal going where you want it to and keep it away from those who might take offense at your offense.

Google some of the ham radio sites for VHF directional antenna drawings and dimensions, they will be found as 2 meter antennas.