poor vhf reception

S

surfbird

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C Dory Year
2007
C Dory Model
22 Cruiser
Vessel Name
Turnstone
Hey folks,

I have a WM vhf550 with a low-end 8' Shakespeare antenna.

The radio transmits and receives at very short distances (a few hundred meters), but I have noticed that my 20 yr old vhf handheld picks up weather channels and some transmissions when the fixed unit does not.

I have checked the connection between cable and radio and it appears fine.

One thing I noticed is a nick through the cable coating -- could this be causing the problem?

Jim
 
It is very possiable that water has gotten into the insulation and coax. This certainly would cause poorer performance. You also want to check the PL 259 (fitting from the coax to the radio). You can replace the coax, but this will involve putting in a new PL 259 near the antenna base, then a coupling and another length of coax with PL 259's on each end. There is a SO 239 which is a female fitting (like on the back of the radio), but I don't seen one for inline which is water resistant or proof. There will be some RF loss with the extra connectors. I personally would replace the antenna (and either get a high end digital, or for the 22, us a 36" metz whip and a base extension. (this gets away from the problems with an 8 foot antenna on the top of a CD 22.
 
I have worked on many VHF systems, mainly on aircraft.

If you can get your hands on a Watt meter, you can answer a lot of questions.

It goes between the radio and antenna.

It will show you the watts that you transmitter is pushing out, and it will show you watts that are reflected back. You may hear it called VSWR meter.

If your coax has damage that is sufficient, it can hurt your transmit and receive capability.

There are a number of things that can cause that, but looking at the coax and the ground plane of an antenna is a good place to start.
 
surfbird":hkmeh0jb said:
Hey folks,

I have a WM vhf550 with a low-end 8' Shakespeare antenna.

The radio transmits and receives at very short distances (a few hundred meters), but I have noticed that my 20 yr old vhf handheld picks up weather channels and some transmissions when the fixed unit does not.

I have checked the connection between cable and radio and it appears fine.

One thing I noticed is a nick through the cable coating -- could this be causing the problem?

Jim
Click to expand...


Make sure your coax cable is not coiled or bunched up behind the radio. If so you need to shorten it & replace the PL-259. :mrgreen: :beer :wink:
 
Thank you everyone for your input.
Well, tsturm's post had me scratching my head a bit.
Although there is a nick in the coaxial sheathing, I also, per installation instructions, did not shorten the cable. Instead, I have it coiled (in 8" loops) and tucked along electrical panel. Not too smart, eh?

So, first I'll uncoil extra cable and store excess away from electronics. Or, can I just shorten it to, say, 3'?
I'll evaluate things at this point and there is no improvement, I'll try to find a wattmeter.

Thanks again.

Jim
 
What is the problem with coiled coax? IIRC, coax is functionally a waveguide, such that it does not matter diddly squat whether it runs straight or crooked or in a figure eight.

I think you guys are thinking of what happens with unshielded runs of twin lead, such as the old, old, old stuff (300 ohm) people used to string from an exterior TV antenna down to the tuner/CRT (=television), back when Moses was a pup. If you coil that suff, it will attenuate the signal down to zip, for sure. Been there, done that!

Coax does not have that property, as far as I know.
 
Small story about coiled cable--
Back when I used to do sound systems for churches and meetings, I was setting up in a church and had not completely layed out the snake (wiring for the mics and speakers) where it would be out of the way. I had it running down the center isle where it had a few coils in it. My main concern at the time was getting the mics and speakers set where I wouldn't get any feed back.
When I turned the system on we had loud rock & roll music bleeding through the speakers. ha :lol:
There were several hushed comments about sacrilege.
I left the system on, walked over and straightened out the snake to remove the music.


Here's alink to the West Marine Advisor on antennes
 
Well, Surfbird, I think you definitely have a connectivity problem. Your C-22 is a 2007 and assuming the VHF is a relatively new unit, that puppy should be overwhelming you with signals compared to your handheld.

Coiling the coax or cutting it short, putting the antenna too close to your other electronics or using a low end Shakespeare would not result in the low signal levels like you are experiencing. Neither would a nick in the coax if it didn't cut deeper than the outside of the shield. A defective antenna? You betcha. A botched up job of attaching the PL-259 plug at the end of the coax? Even more likely. Yah, like an earlier poster mentioned, salt water or even fresh water into the coax "nick" is a possibility but again, you have a new boat and if the nick is inside the hull that possibility is extremely rare. Heck, your radio itself might be defective....

If it were me, I'd first replace the PL259 plug. The KISS solution. if that didn't work I'd then cut a piece of wire 8-10 ft. long, attach it to the center conductor of a PL-259, screw it onto the back of the radio and compare signals with your handheld. DO NOT TRANSMIT! You should hear a marked difference in the number of VHF transmissions you're picking up. If you don't, then it's time to get your radio fixed. If you do, then you have two choices:

1) Buy a new antenna

2) Cut the coax on the antenna side of that nick, put a PL-259 on and connect it to the radio. Even if you have to dismount the radio temporarily. If that solves the problem just make a jumper coax cable that will get you to your radio or see 1)

Don

P.S. Though I hate to admit my age, I first started troubleshooting and repairing HF/VHF/UHF radios and radars 52 years ago and have been a radio amateur since 1959. My personal installation is a Digital 8 footer connected to a relatively inexpensive VHF radio on a boat that's in a salt water marina 90% of the time. My coax is just long enough to dress into the helm wiring and reach the radio. Maybe 4 ft. tops. The only interference I get is digital "hash" from my C-80 located less than 10 inches away from the radio. The signal levels I get are so high that simply setting the squelch where it doesn't trigger from C-80 hash works for me. If I were terribly pressed to hear an extremely weak signal all that's needed is to turn off the C-80.

Then again, my opinion is, as always, worth the price you paid for it. :lol:
 
Agree with Sneaks. I had made an assumption that you had a good signal, and that it has decayed with time. Certainly a bad antenna, or most likely a bad PL 259 connection is a cause of the problem. Incidently the crimp on PL 259 plugs are no where as good as a properly soldered plug. I have seen this demonistrated may times. Unfortunately many people do not know how to properly solder the PL 259 plug.
Here are a couple of articles on proper technique:
http://www.seed-solutions.com/gregordy/ ... erCoax.htm
http://www.hcarc.us/articles/soldering% ... ectors.htm

There are several pitfalls. One is that you have to solder the braid to the connector, thru the holes in the body. Second, if you get the connector too hot, you can distort the phenolic insulator, which holds the center connector.
I use Vise Grips as heat sinks, and I small torch. If you use a soldering iron, a 100/150 watt iron is marginal; Far better is the 200/260 watt gun. (you can get cloth cutting tips for these irons, for sealing acrylic fabrics)


As long as you don't go less than 3 feet, cutting the coax should not be a problem.
coiling should not cause the problem.

If you have a Byrd or Telewave Watt meter you can obtain excellent information. The small Shakesphere SWR meters which go in line, are fine for SWR measurement, but are not highly accurate as for out put.

There are certainly bad antennas. I take an antenna analyzer with me when I buy an antenna and check it before I leave the store. I have found some with very high SWR. Personally I have had better luck with Digital antennas, than the Shakesphere.

Buying one of the $40 inline VHF SWR meters is a good idea. Radio Shack had RF output meters--which were in the $30 range. Mine is not super accurate, but I can calibrate it with a radio where I have a known power and then use the relitative readings. The RF power meter has an antenna and receives the radio signal.

I also have an MFJ 259 antenna analyzer, but that is far more than what the average boater needs.
 
I clicked on this link because in my sea trial last week, my "new to me" radio was definitely a bit weak. I think this discussion will be useful to me, but not before I pull out a radio dictionary to figure out what half the things in this thread mean.

I'm continually impressed by the knowledge base in this forum.
 
This week I also found that my new Standard Horizon VHF was weak in receiving and transmitting. I was trying to talk with another boat 7.5 miles away and it was less than marginal. My CB also is not functioning well.
My antenna is a 10 yr. old 8' Shakespeare combo VHF-CB.
May be time to "deep six" that antenna for a new digital.
Is there a CB digital also???
 
Antenna longvity depends on how they are stored. Often by 8 to 10 years the gel coat or paint on the fiberglass is going, and there may be some corrosion in the soldered areas, wires etc. Also coax can get water in the insullation.

One store mentioned a "black" CB antenna--don't see any on the Digital site. (Digital is a manufactuer--not a type of antenna).

Siddfynch, feel free to ask about terms. If you don't know, there is a good chance that others don't. This site is about eduction as was as comradary.
 
Bob,
Thanks for getting me straight on the digital thing. I was looking through West Marine last night and could not find anything on digital. Now I know why.

We had our last trip out in the CD today. It is on the trailer until next April so I have lots of time to get my VHF problem sorted out.
The 1st thing is to get some new 259 connectors, cut all the extra co-ax off and replace the connectors. Then check it out with my SWR meter.

Do you have a suggestion for a new VHF ant.??? They run from $59 to almost $500 and look alike. I am definitely going to get separate ant.'s this time. No VHF-CB combo. Any guidance would be appreciated.

Thanks for you usual good help.

Jack
 
If you want an 8 foot 6 dB gain marine VHF antenna, I like the 529 by Digital. I have found them to be most reliable as far as the SWR (Standing wave ratio--basically the power output vs the power which is reflected back to the radio. if the SWR is too high, then the output circuits on the marine VHF radio cut down the power delivered to the "final" output transisters, to protet them from a mismatch.) These antennas are actually measured at the factory to have an SWR of 1.2/1 or less. Anything less than 2.0/ 1 will still transmit, but the signal will not be as good. The Digital has gold plated connectors, to decrease corrosion. and the exterior is urethane painted to get away from the detoration of the fiberglass gel coat. I have taken apart both Shakespeare and Digital antennas (OK I broke them on trees etc--my goof), and I felt that the workmanship on the Digital was better.

Antenna gain--this is the theoretical increase of signal which comes from making it somewhat directional in the horizontal plane (beam width in the horizontal plane)--visualize that the signal with a low gain antenna is more like a balloon and will still transmit a good signal even if the boat is heeled to 40 degrees. The higher gain (such as 6 dB is more like a Frisbee, and if the boat is healed, to a certain point there will not be as good a signal along the horizon. Since our C Dories only heel a few degrees, this works the best for power boats The 9 dB antenna is more like a flat disc and is best for land based antennas, where there is no heeling factor.

One of the problems with the 22 is that the cabin house is short enough, that with an 8 foot antenna folded down, it overhangs the cocpit and people grab it--and it is easily broken. My solution on the 22 was to use a 36" SS whip, with a loaded base--the same antennas I have used on sailboat masts. I then put a 2 foot SS extension mast on it. This gets the antenna up a little higher, but the over all length is less than the roof, and it will not be broken. The penality is that the gain of the 36" whip is only 3 dB--so a little less effective RF radiation.
 
Hi Jim,

I may have missed it, but; in looking down thru the thread I don't know if
you have tried to swap the radio with a known good unit connected to the
coax in question before you start the cable work process.

All the suggestions presented here a very good ones and should have you
back on line in no time. At least this is something you can do in the 'drive',
on the trailer.

Art
 
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