VHF Marine radio SWR

[moose]

I installed a VHF in my boat when we got it really for emergencies. (Had an experience offshore a long time ago and the VHF probably saved our lives.) Every time we go out I turn it on 16 just incase.

We were doing a poker run a couple weeks ago and was talking to another boat on ch72 but lost him after only a couple hundred feet.

Now, I know all the variables that come into play here but I want to know if my setup is doing ok. This isn't the first time this has happened.

I tried to hook up my little RatShack meter but the readings were to erroneous. Do I have to find a meter that will handle VHF FM?

If so, any suggestions?

Thanks!

 

[KE5MC]

Without experience using the RatShack meter in a good configuration its hard to tell at this point what it is telling you. Even in a good configuration the results may be meaningless. Best action is find a meter for that frequency range and see what you have.

Range of only a hundred feet could be a bad feedline. Easy to check with a multimeter as the problems is likely an open/shorted cable.

Good Luck, keep us posted.

Mike

snip...
but lost him after only a couple hundred feet.

snip...

I tried to hook up my little RatShack meter but the readings were to erroneous. Do I have to find a meter that will handle VHF FM?

If so, any suggestions?

Thanks!

 

[Beetle]

Some HF-rated meters might be okay at VHF, but I wouldn't trust any one of them. VHF Power/SWR meters are widely available (check MFJ) and they're much better designed and laid out for the higher frequency. And you should be able to use a VHF meter on HF (not the other way round).

And as Mike said, check your feedline carefully for water intrusion, either through cracks in the jacket or through the connectors.

 

[moose]

Found it.

Got to really digging into the install that the dealer did and wasn't impressed at all. The SO259 on the back of the radio was loose so tightened that up. I got my PRO-106 scanner out, tuned it in, put a rubber band on the mic and went to shaking everything. First off the excess coax was rolled into a perfect RF choking coil, dummies...

Kept shaking and finally got a crackling about halfway back. Couldn't see any signs of fatigue on the jacket but could hear and obvious break/short. Tossed the coax and installed a new piece PROPERLY.

With it sitting on the trailer in the driveway at 13+ volts (batt charger) I got about three miles away as the crow flies and could still pick him out with the scanner. I'm ok with that.

Thanks to everyone for the help. Will still shop for another SWR meter that will work on both but that's another discussion for another section.

73's
Moose

 

[KE5MC]

Moose,

Glad to hear you found the issue and resolved it.

Just a couple of minor points.

Coiled coax is not so bad. Some antenna's could use a balun (ugly) to keep common mode RF off the braid, but they are installed at the base of the antenna. At VHF an easier to apply choke is a clamp on ferrite if any is need at all. At most you lost a little power to the antenna for a longer than needed feed line.

Battery chargers have outputs suitable for batteries, but not radios. The RMS reading looks good, but it might have spikes that exceed the radio's DC input specification. Usually the components are overrated (voltage) and will tolerate some abuse for a short time.

Mike

Found it.

snip...

First off the excess coax was rolled into a perfect RF choking coil, dummies...

snip...

With it sitting on the trailer in the driveway at 13+ volts (batt charger)

snip...

73's
Moose

 

[moose]

Points understood.

It was a 50' piece of coax that I pulled out. (It's only a 20' boat) they had the coil and the rest of the wires (sounder, FM radio, 2nd battery) all tie strapped together. Also, the battery tender was on the batteries themselves, we weren't running the radio solely with a charger. I just said that so you could know we weren't running at a less than optimum voltage.