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Author Topic:   VHF Radio Installation Advice
sternorama posted 05-22-2008 01:29 PM ET (US)   Profile for sternorama   Send Email to sternorama  
Looking for advice on VHF radio installation. (I know there is a thread on this in the archives, but my searching did not yeild the results I was hoping for.)

The boat has dual batteries and a OFF-1-BOTH-2 switch. I assume I want to connect to the (+) connection on the switch, and use an in-line fuse?

Also, I purchased the GAM antenna that has been discussed here. I am assuming that this comes with a length of wire. Should I leave that wire the length that it is and just coil up the excess? What are the implications of coiling an antenna connection wire? Does changing the length of the connection wire require retuning the antenna?

Any tips will be appreciated. The last radio I hooked up on my old Whaler I connected to the terminal block, but this Edgewater 175cc has a different integrated switch and circuit breaker type of connection panel with pigtails daisy-chained from breaker to breaker. I'm not sure what to call it.


jimh posted 05-23-2008 12:17 AM ET (US)     Profile for jimh  Send Email to jimh     
If you are asking about the GAM ELECTRONICS SS-2 antenna, it does not include any feed line. You should order the ADAP-I or ADAP-II mount accessory. The ADAP-I or ADAP-II mount includes about 20-feet of RG-58C/U, which is the highest grade MIL-C-17 specification coaxial 50-ohm transmission line, AKA "wire."

An article in the reference section gives details about the GAM SS-2 antenna and the GAM ADAP-II mount accessory:

jimh posted 05-23-2008 09:48 AM ET (US)     Profile for jimh  Send Email to jimh     
What are the implications of coiling an antenna connection wire?

If the "antenna connection wire" is a coaxial transmission line which is terminated into an antenna whose impedance is a good match for the characteristic impedance of the transmission line, the coaxial transmission line can be routed or coiled into any shape without affecting the flow of radio frequency current on the inside of the transmission line as long as the minimum bend radius for the cable is observed. Radio frequency current travels on a coaxial transmission line between the inner surface of the outer conductor and the inner conductor. The transmission line cannot tell if it is arranged into a solenoidal coil or a pretzel.

When an antenna is fed with a transmission line (of any type) and the transmission line is in the field of radiation of the antenna, it is possible that antenna currents can flow on the transmission line. If the antenna is fed with a coaxial transmission line, the antenna currents will flow on the outer surface of the outer conductor of the coaxial cable. Generally the arrangement of an antenna and its feed line is made so as a to minimize the flow of antenna currents on the transmission line. To suppress flow of antenna currents on a coaxial transmission line, it is common that some form of radio frequency choke be fashioned on the transmission line. This RF Choke can take many forms. In some cases decoupling sleeves are used, and often these sleeves are inside the antenna housing, particularly in the case of vertical antennas fed from their base. In other cases ferrite beads are added around the coaxial transmission line to create RF chokes. A simple technique to create an RF choke is to wind the transmission line into a solenoidal coil. The inductance of the coil suppresses flow of radio frequency current on the outer surface of the outer conductor, but has no effect on the flow of transmission line current inside the coaxial cable.

There is usually no valid electrical reason for making a coaxial transmission line any particular length as long as the transmission line and antenna are well matched in impedance. In some cases a transmission line is made part of the antenna matching system, and its length is important and should not be changed. However, in most marine antennas this is not the case. A transmission line that is not a critical length because it is part of the antenna matching network needs only to be as long as necessary to connect the transmitter to the antenna. However, in electronics there is a an old rule that says, "Any cable cut to length will be too short." Also, because many boaters are not expert in the installation of coaxial connectors, there is some prudence in not cutting off a factory-installed coaxial connector just for the purpose of shortening the transmission line a few feet.

The preference for a transmission line to be as short as possible is to reduce loss of signal in the transmission line. In the case of a VHF Marine Band radio, the loss in the cable is not so high that a significant reduction in loss can be made by cutting a few feet of excess from the line. In a transmission line of 20-feet of RG-58C/U the loss is on the order of 1-dB per 20-feet. Cutting out five feet of cable will reduce the loss by 0.25-dB, which is generally insignificant. There is hardly any situation in radio communications in which a 0.25-dB difference in signal strength will be observable by those using the radio.

jimh posted 05-23-2008 09:53 AM ET (US)     Profile for jimh  Send Email to jimh     
Does changing the length of the connection wire require retuning the antenna?

An antenna is not tuned by its feed line. The resonance of an antenna is established by the antenna's physical arrangement, the length and diameter of its conductors, and by their resistance to flow of radio frequency current.

sternorama posted 05-23-2008 11:55 AM ET (US)     Profile for sternorama  Send Email to sternorama     
Thanks for the notes. The reference article was a big influence in my decision to purchase the GAM antenna, and I did order it with the ADAP-II mount.
jimh posted 05-23-2008 02:39 PM ET (US)     Profile for jimh  Send Email to jimh     
The ADAP-II feedline will not be terminated in a coax connector; you will have to install one yourself.

If you want to use a PL-259-style (UHF-Series) connector, there are many options available besides the classic PL-259 and UG-175 adaptor for RG-58-size cable.

If you do use the classic PL-259 and UG-175, be very careful trying to make a solder connection to the shield. This operation requires a lot of heat, and too much heat will soften and deform the solid polyethylene insulation of the coaxial cable.

Having been trying to assemble these cables for over 40 years, I have found a technique which reduces the tendency to need too much heat. I pre-tin with solder the holes in the PL-259 connector before assembling it to the cable. When the cable is not assembled to the PL-259 connector body, you can use as much heat (within reason) as you like on the metal connector to pre-tin the holes around their circumference. With the circumference of the hole in the PL-259 connector body tinned, and the metal connector perhaps a bit warm still, you will find that the solder will flow with less heat when you re-assemble the connector on the cable and try to solder the shield to the connector. (Be sure you are not using eutectic solder, and use solder with a low melting point to help, too.) When pre-tinning the connector holes, don't let solder flow into the inside of the connector body, or you will have trouble assembling it. After tinning and before assembly of the connector to the cable, it is also a good idea to thread the UG-175 adapter into the PL-259 a few times to clean up any solder flash that remains from the tinning.

Instructions on PL-259 and UG-175 assembly to RG-58:

sternorama posted 05-27-2008 06:06 PM ET (US)     Profile for sternorama  Send Email to sternorama     
Well,I have completed the install. Based on prior follies soldering the PL connector I opted for the mechanical centerpin type. I had my doubts as I was pushing the "teeth" into the sheath with pliers per the directions-it seemed a bit hokey. I was seriously thinking about how an expert article on how to professionally solder a PL connector would be good right about now. But I stuck with the mechanical connector, and it seems to be doing the trick.

Maybe I'll practice on some scrap cable, and if I can get the desired results I will change it out. I think the soldered connection would be better in the long run due to possible movement between the wire and the crimped connector.

For power, the center post on the Rule switch seemed to work, and I like the ability to shut off "all" (including the VHF now) while on the trailer.

Thanks for the soldering tips, jimh.

By the way, I used the reference article tip on shortening the threads on the antenna mast so as to fit cleanly in the ADAP mount. I purchased a mast with CRES ferrules, so it was quite a chore! I used a 4.5" grinder with a cut-off wheel, and I cut slow and dipped the work end in a bucket of cold water frequently to keep from damaging the mast from the heat during the cut. Then I "remodeled" the thread form with a Dremel and a small grinding stone so it fit smoothly into the ADAP mount. To bring the cable into the console I used a small clamshell vent.-G

Chuck Tribolet posted 05-27-2008 08:50 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
I've been using the Center Pin connector on my radio for
years, no problems.

I can solder, I have a really bad boy soldering gun, and
the radio connectors have always been problematic.

On my GPS, I need to replace the BNC Center
Pin connector every four or five years. It's due again --
the GPS kept loosing lock Sunday, fiddle with the connector,
it came back. This time I'm going to cut the heat shrink off,
tighten things, put it back. I do have a new connector in the
tool box.


sternorama posted 05-28-2008 12:48 PM ET (US)     Profile for sternorama  Send Email to sternorama     
Chuck, do you think the connector fails at the sheath or at the "pin" contact? Maybe a hybrid mechanical/soldered connector would be the ultimate?
jimh posted 06-01-2008 04:12 PM ET (US)     Profile for jimh  Send Email to jimh     
For the ultimate installation for a transmission line of RG-58C/U use a UG-88/U BNC-series connector, and install a between-series adaptor which has a BNC jack and a UHF plug on the radio's SO-239 jack. The BNC connector uses a bayonet or twist lock mating, which makes it very handy if you often want to connect and disconnect the transmission line from the radio set.
jimh posted 04-18-2015 10:14 AM ET (US)     Profile for jimh  Send Email to jimh     
For more advice on the process of installing a VHF Marine Band radio on a small boat, see my recent article at

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