VHF Antenna question

Spike · Posted: Wed Jan 31, 2007 9:14 pm Post subject: VHF Antenna question

Maybe you all can help answer a question for me. Can you cut short the antenna cable, and not lose radio preformance? Thank you to any and all
Chuck
Bootleg Hooch

Dreamer · Posted: Wed Jan 31, 2007 9:46 pm Post subject:

Yes you can! I believe the recommended minimum is 36". The only critical length is the antenna itself.

416rigby · Posted: Wed Jan 31, 2007 9:49 pm Post subject:

Yes.

The antenna instructions state as much, and tell you how to do it. You'll need a new connector, and it will contain instructions for installation. The folks at your local marine supply should be able to help. If I remember correctly, there is a minimum recommended length for the cable, maybe 6 feet, but I can't recall offhand.

Rick

Edit...dang, Roger, ya beat me to it while I was typing my reply. Laughing

thataway · Posted: Wed Jan 31, 2007 10:49 pm Post subject:

Roger on Dreamer is correct--3' is the minimal length for the VHF coax. I like to leave a bit more--that way you can replace the PL 259 connector and have enough slack to work with if you remove the radio.

Spike · Posted: Thu Feb 01, 2007 9:30 pm Post subject:

Thank you everyone. Was hoping I could trim the cable a bit more. Oh well will go to plan B

Chuck
Bootleg Hooch

Sea Angel · Posted: Fri Feb 02, 2007 5:57 pm Post subject:

Another 2cents..

Not only will you want to keep enough coax for future connector replacement that was so porperly noted, but also what I call a service loop. This is so you can move the radio into a maintenance check position. This would allow you to add a meter to the back of the radio and plugged into the coax line to check the radio's output and its relative SWR to the antenna.

The other item would be a 'near field' location where you are holding the mic. This is at a location that has minimal RF interference from the radiated power of the transmiting antenna via the RF getting into the mic circuit. Most manufactures recomment a distance of 3 ft from the antenna.

If you have any concerns of how to replace either the small, BNC type, or the standard, PL259 type , connectors you should be able to find someone who is a HAM or other tech type to do this for you.

Cutty Sark · Posted: Fri Feb 02, 2007 6:29 pm Post subject:

Ok, coax whiz's Wink

. Here's one for you, My cable is too short, the run from my electronics arch all the way to the shelf above the helm is just bit longer than my cable. I went to west marine, and the guy said just adding a splice is a bad idea because it will degrade the signal. He suggested going to radio shack and picking up some kind of signal booster attachment. And using that to splice the cable. Is there a better way? Any suggestions or tips? Thanks in advance.

Sark

Spike · Posted: Fri Feb 02, 2007 8:34 pm Post subject:

I wonder if just getting a new antenna would be cheaper than a booster, splice, and connectors? I paid a little less than $80 for a new 8 ft antenna. Just a thought
Chuck
Bootleg Hooch

Alyssa Jean · Posted: Fri Feb 02, 2007 8:45 pm Post subject:

Anything you put in series with the antenna cable will degrade the signal, this includes connectors, adapters, etc. You should be able to have another cable made up the correct length for not too much out of your wallet.

Sea Angel · Posted: Fri Feb 02, 2007 9:43 pm Post subject:

Change from my 2 cents - 1 pennys worth -

IHMO:
I would caution against anyone using any 'booster' to be used by, or with, the VHF Marine transmitter. The VHF Marine radios are FCC type accepted and can't be modified in this fashion without violating the regs. The max power out is also a part of these regs. as 25Ws. If by a 'booster' is implied for the receiving signal, well that would probably be OK. However these radios are transceivers, meaning that they are not a separate radio transmitter and receiver, but combined into one unit.

As to the short coax-
Sark, if your coax is of the RG-8X version, you will probably not notice any difference if you added a short jumper with a barrel in line as long as each connection high quality and is good and firm. Even if not RG-8X, I would use the RG-8X as a jumper, verse RG-58 types. I use RG-8X for these frequencies and the loss for the short run you imply will be very small.

I would suggest you try adding a jumper; try a long haul communication with someone you have talked to before, and see if it meets your range needs and experience. If so, your only out the time and a few $$ for the jumper.

I would also suggest that if you can get a copy of the Powerboat Reports, Feb. 2007, they have an excellent article and review on 10 different VHF antennas starting on page 12, thru 16. Their comparison was, in part, covering the 8-foot, 6db-gain, antennas that ranged from abt $36 to $159. The manufactures are COMROD, DIGITAL MARINE and SHAKESPEARE.

Hope I did not add too many 'fly spects' to the questions answer.

Think I'll head out to modulate the feather rester so I can up early to go to the Atlantic Boat Show in the AM. in VA Beach.

thataway · Posted: Fri Feb 02, 2007 9:47 pm Post subject:

You can get a double female connector PL 258 This will "cost" you about 1 db of signal strength, not enough to really worry about. If the antenna is over 5 years old, you might consider it a wiser move to buy a good new antenna. With time in the marine environment, there is some moisture intrusion into the insulation in the coax. Not all antennas are equal--and I have found some which were very badly tuned, causing as much as as 50% reduction in transmitted power. Shakesphere also makes a "splice" PL 258 CPL G--I do not like them as well as a properly soldered connector, since the coax is just pierced and the connection is not as good as a solder joint. Also not all PL 259 and 258 are equal, some are better and less lossy...

Don't try and solder splice the coax. It is generally not a good idea.

Cutty Sark · Posted: Fri Feb 02, 2007 10:01 pm Post subject:

Ok, I have a 4 foot shakspeare 5400xt galaxy antenna( I think) Paid about 120 for it after a small discount., It is an ok antenna, I just replaced it. I can make the run, but not on the path I would like to route it on. I got a 4 foot job because it's up on the arch, and handling a 8 footer up there seemed like a pain, so it is only 3db to begin with. My last one recently shattered hence the replacement. I have extra cable but would need the splice or the double female dohickey. I stopped by radio shack today and nada. So.... I guess I will try the extension, and see what happens. The booster I will stayaway from as well as a homeade splice Laughing

. I believe most of the antenna's come with the same length of cable which is 20 feet I think? Can I buy a longer cable and connect it at the antenna end somehow? I would rather avoid losing any performance since it only a 3db antenna.

Sark

thataway · Posted: Fri Feb 02, 2007 11:22 pm Post subject:

To my knowlege the only antennas which come with a connector at the base are the 36" whips--either Metz or Shakesphere. I recollect in the past seeing a fiberglass VHF antenna with a short connector--but the disadvantage is that the chances of water intrusion is greatly increased. (there are self amalgamating tapes which will water proof a barrel connector. I don't know of any way of making the co-ax longer right at the base, better to use the connectors inside.
Bob Austin

Sea Angel · Posted: Sat Feb 03, 2007 9:45 pm Post subject:

Bob,
I think COMROD makes a VHF Marine antenna that has a base fitting that would meet those needs. They are very pricey, though. I don't have the article at my fingertips, but will try to find it and pass the model on if anyone needs it.

thataway · Posted: Sat Feb 03, 2007 10:44 pm Post subject:

Apparently Practical Sailor mentioned the Comrad antenna. This may have a PL 258 type of female plug on the antenna base. I know that some of the Comrad antennas are dipoles, rather than 5/8 or 1/2 wave whips.

There was another high end VHF antenna which had a short lead with a PL 258 type of female plug on a sort lead out the side of the base...

Thanks,

Bob