VHF troubleshooting

[janders]

We're having a problem with our VHF. We can transmit great but can't receive anything but the most powerful transmissions, basically anything from Coast Guard Seattle Sector and one WX station. We can't receive transmissions from a boat 300 yards away. We've had boats a few miles from us receive our transmissions but we never hear anything coming back.

Here's our setup:

Shakespeare antenna on top of mast.
60' of RG8X running to the keel step.
30' of RG213 coupled to the RG8X running to an ICOM 422 at the nav desk.

I pulled the radio out and hooked it up at the base of the mast and got the same results. Transmit fine, no reception. I also tried with a different radio, an older ICOM. Same results.

So of course, the problem seems to be somewhere along the coax run through the mast or the antenna. We had the mast stepped last summer and replaced the antenna, the antenna connector, and about 8 inches of coax that had gotten water intrusion. We also waterproofed the crap out of the connection to the antenna in hopes of not having to do this again.

Before we send someone up the mast, does anyone have any idea how we can better pinpoint where the problem might be? Or what the problem might be?

[btrayfors]

You need to replace the RG8X coax. Even if you lopped off eight inches of it, water could well have wicked much further down the cable. If you possibly can, use RG213 or RG214 (double braid) to replace it (not RG8X unless you absolutely have to), making very sure of the correct connection of the UHF (PL259) connectors. It's unlikely that the antenna itself is the problem.

You can test this by using a shorter length of RG8X with PL-259s at each end. Send someone up the mast, and connect one end to the antenna. Connect the other end direct to the radio. Now, see what you've got.

If you had a decent antenna analyzer (about $250 and up) you could probably diagnose the problem with the coax, but it's better to just replace it.

IMO,

Bill

[hellosailor]

1. Unplug antenna cable from radio.
2. Plug in "emergency antenna", typically a magmount or clamp mount about 19" tall with a dozen feet of cable on it, sold in a plastic tube.
3. Test radio.

If it works--you need to replace the coax and/or antenna. If it still doesn't work, your radio has something blown in the receiver circuit, and needs repair/replacement. Considering that repair labor can run $75-125 for the first hour...replacement, unless you can open it up and find something subtle and obvious, like a cold solder joint that is easily repaired.

You can also make a jury-rigged emergency antenna very easily from a piece of coax with just the radio connector on one end, i.e. ten feet of an old cable. At the cut end, make a slit 1/2 meter long in the outer insulation--not the braid. Peel off the insulation, then peel the braid back OVER the outside of the cable, keeping it intact as a tube around the cable. If you can't do that, just slice off another 1/2 meter of cable--a bit longer actually since it will change in length, and slide the "tube" of braid over the outside of the cable, then solder it together at the "turned" point.

Put a loop or tie a string to the top end, so it can be hoisted or hung vertical.

You've now got a length of cable with a radio connector at one end, and a metal "tube" near the other end. As long as the "tube" and the center section that was under it are both about 1/2 meter long, you'll have an effective antenna. AFAIK this is properly called an 'end fed coaxial dipole' and often confusingly called a "bazooka" antenna, which is something entirely different.

The radiation pattern and gain will be somewhat different from a marine antenna--but this is perfectly matched to your radio and perfectly good for testing and emergency use. The 1/2 meter measurements aren't dead on, if you have an SWR meter and a few formulas you are welcome to tune the antenna more precisely. But, it is a cheap way to have a working antenna for radio testing. And easily stowed.

[janders]

Originally Posted by btrayfors

You need to replace the RG8X coax. Even if you lopped off eight inches of it, water could well have wicked much further down the cable.

Thanks for the quick reply, Bill! That's the nightmare scenario. Mostly because RG213 is so much thicker than RG8X that I doubt it would fit in the existing conduit. That's going to turn into a "pull the mast and re-wire it" project I'm afraid. I still have hope for the RG8X yet. When we cut it back, we cut it back to the point where we found shiny uncorroded braid and center conductor. Any corrosion on that connection would have come after we replaced the connector and we did a decent job sealing up the connection (adhesive lined heat shrink + self amagalmating tape + liquid electricians tape).

Maybe this is just my way of sticking my fingers in my ear and going LALALA until I hear what I want.

[Ziggy]

Originally Posted by janders

We can transmit great but can't receive anything but the most powerful transmissions, basically anything from Coast Guard Seattle Sector and one WX station. We can't receive transmissions from a boat 300 yards away. We've had boats a few miles from us receive our transmissions but we never hear anything coming back.

It doesn't seem likely that a bad coax would let you transmit but not receive. I have a couple of questions:

1) Have you tried transmitting at low power (1W)?
2) What happens when you turn down squelch--do you get the usual level of static?

If you have a spare antenna, try reception with it connected directly to the output using a short section of coax.