VHF Radio has low power output

ooootis

Petty Officer 3rd Class
Joined
Apr 26, 2003
Messages
80
Hey all. Here is whats going on never transmitted on the radio but it appeared to work fine could hear everyone so to speak. I forgot to drop the whip coming outta the ramp area and of course being 8 foot long a tree whacked it. Replace the ant. with a upgraded from what was on the boat.<br />SWR meter show a loss more towrds the right of the meter. i used a push on 259 connector so tried shanging that to a soldered one still no joy. Radio is I com 402 with a sheakspeare 5225<br />Galaxy ant.use RG 8 coaxial. old one was 5102 Centennial using RG 58 coax.
 

Reel Appeal

Chief Petty Officer
Joined
Aug 19, 2002
Messages
566
Re: VHF Radio has low power output

Not sure what you mean when you say "shows a loss right of the meter"? Is the radio on high(25watt)?<br />The antenna connector is critical to radio performance.http://www.shakespeare-marine.com/antennas/ant-faq.htm<br />Hope this helps...<br />They also make a new center pin connector(very easy install/no soldering/great performance)<br />Just a note:Your antenna cable must be at least 3'ft. long. The outer(stranded) wire on the cable is the "receive" wire.Center(solid) wire is for transmit.You can also obtain silver solder for electronics.
 

ctlincoln

Cadet
Joined
Jul 23, 2003
Messages
10
Re: VHF Radio has low power output

Not sure if I can help but I spent 10 yrs in the Air Force as a ground radio maintenance journeyman (funny millitary title for radio tech) and I think I may know what your problem is. Sounds like your antenna maybe the wrong lenght causing you to get reflected power back to the transmitter. I would look and see if there is a guide to cutting the antenna to a specified length for the operating frequency the radio is using. More than likely there isn't and its a fixed antenna built for that radio. If so make sure the radio isn't shorting to a ground some where in the boat. Try transmitting the radio while the boat is on the trailer. Those rubber tires will not allow your boat to ground. If it works out of the water then your radio is shorted to the boat somewhere from the antenna or coax cable. It may also be the wrong antenna for the radio. These are just some ideas that first come to mind that I have seen in the past. Also try other frequencies and see if the problem is frequency specific or if it is the entire spectrum. Let me know what happens and I will see if I can assist you more.
 

kd6nem

Chief Petty Officer
Joined
Jul 25, 2003
Messages
576
Re: VHF Radio has low power output

That "SWR meter shows a loss toward the right side of the meter" statement is still confusing. Are you looking at the SWR mode (reflected power) or forward power (normal mode)? Higher SWR indicates an antenna mismatch (or bad connection). Mismatch mean loss of performance and is hard on the transmitter. If SWR is worse on the lower frequency end of the band the antenna needs to be slightly longer, worse on the higher freqencies then shorten it a tad, working step by step in very small increments. Steel antennas usually have a little set screw below where the "stinger" (top, skinny part) is attached. Loosen it up and move it the needed direction, then tighten and recheck. In the power mode is the transmitter putting out less than it used to as checked by the same meter? Believe it or not more power isn't usually nearly as helpful as a better antenna and less lossy feedline. Sounds like you are in good shape thataway so long as all your connectors are good. Make sure they are good should be the first step, tuning the antenna is a distand second priority, so long as it is indeed a marine band antenna. By the way, both inner and outer conductors ARE necessary for both transmit and receive. You can sometimes receive so so with only the center conductor if the signal is coming in strong, but that is not how it should be. If it is hearing more distant weaker stations OK you probably aren't too far from being in good shape. By the way, if your swr meter is not rated for the marine band frequencies, it is probably useless. A CB meter is almost certainly not accurate here. If the meter has an instruction book it can be most helpful, though some can get pretty complicated. By the way, make sure you seal all your coax connections with weatherproof tape or putty once you get it right, or else it won't stay good for long.
 

Boatist

Rear Admiral
Joined
Apr 22, 2002
Messages
4,552
Re: VHF Radio has low power output

Ot15<br />To start with a Shakespear Galaxy 5225 antenna is a great antenna. It comes with RG-8X coax not RG-8. RG-8X is much smaller and requires an adapter to fit a standard PL259 connector.<br />The antenna is a 5/8 wave and requires no ground plane or tunning. DO NOT CUT THE ANTENNA. Also you do not have to tune the feed line. If you have a high SWR then one of two things likely, either you have a short in the cable/connector or a short where you brough the cable inside the hull. This antenna with any length coax will have a SWR less than 1.5 to 1. Make sure your SWR bridge is rated for VHF frequency. Both Radio Shack and West Marine sell gold plated coax connectors and and adapters for RG-8X.<br /><br />When checking your SWR to make sure Coax not shorted do it on your 1 watt power level and not on channel 16 or 22. Adjust your SWR bridge to full scale in the foward direction then switch to the refelected position. You should get reading far to the left not in the red area and less than 1.5 to 1. The ICOM 402 also a very good radio and the transmitter will shutdown to protect it self with SWR over about 2.5 to 1.<br /><br />The Galaxy 5225 has a 6 DB gain and transmittes and recieves in a very narrow horz plane so antenna must be mounted straight up to work correctly. If you lean it back then you will be transmitting into the SKY off the bow and into the WATER off the stern and get very little range. <br />One thing that can affect your SWR with that antenna is if you have it mounted on the side of a metal cab then can get some refelected power back off the cab. You can add a short antenna extension to get antennna clear of the cab.<br /><br />RG-8X like all coax is an un-balanced line and the center connector is used for both Transmit and Recieve. The outer braid is used as a shield and a ground wire and grounded to both the radio frame ground and the battery ground.<br /> <br />It is a shame you got so much incorrect information on this thread. Some infomation would be correct for a 1/4 wave antenna that requires a ground plane and antenna or feed line tuning.
 

ooootis

Petty Officer 3rd Class
Joined
Apr 26, 2003
Messages
80
Re: VHF Radio has low power output

thanks for the straight scoop boatist. i do have the wrong type of swr meter my antenea is mounted on top of the T tops and is straight. I tested the unit with the new antenea in the yard and could only get a transmission a mile away. did radio check on water and never got a responce so i thought it was not up to par. i will purchase the correct SWR and look at stuff again <br />thanks.
 

Boatist

Rear Admiral
Joined
Apr 22, 2002
Messages
4,552
Re: VHF Radio has low power output

QT15<br />If your are looking for a VHF SWR meter that will work on the Marine band also check some Ham Radio outlets as may find a better price.<br />Any SWR bridge that will work for the 2 Meter ham band will work, also the 220 and 440 bands. The one I use is a MFJ-812 and about $35. <br />Good Luck and let us know what you find.<br /><br /> http://www.aesham.com/ <br /> http://www.hamradio.com/ <br /> http://www.iboats.com/mall/index.cg...&cart_id=492287474&current_category=swr meter
 

duck-n-pond

Petty Officer 2nd Class
Joined
May 27, 2003
Messages
124
Re: VHF Radio has low power output

All good suggestions above. Most marine antennas are pretuned for a 'band' of frequencies as stated, and come with its own cable. On that note, are you perhaps using the origional cable or using an extension cable? Any dampness in the cable will cause backpower. Another thought (although if you don't solve from the suggestions above, get a radio tech), I once worked on a radio that a customer installed themselves, and they had cut the antenna cable to fit the job. Never do this. I found that the cable was cut to a length that was a direct wavelength harmonic from the transmitted frequecy causing reflection within the cable - the same thoery as people above were indicating the tuned whip may be the wrong length. If I added the vswr in, the radio transtitted fine (protected radio would not tx on high backpower). Real freaky trouble. For an experiment, I chopped another 10 inches off and all cleared ok. This is a real shot in the dark, but every thing else seems covered above.
 

BLU LUNCH

Lieutenant
Joined
Aug 8, 2003
Messages
1,316
Re: VHF Radio has low power output

Go to the ARRL website and find yourself a ham radio club or go to BUCKMASTERS CALLBOOK site and you can pull up alist of hams in your town. Almost any ham would help you find your problem and tell how to correct it. It sounds like swr or bad co-ax. it's a easy fix ...good luck....Ted
 
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