Problems transmitting on VHF with engine running

LawranceT

Recruit
Joined
Jan 1, 2003
Messages
3
I have a Swiftech M-168 VHF marine radio which appears to be working fine apart from when I try to transmit with my outboard (old Johnson 50hp) running. When I try to transmit I am told that my transmittion is very broken and crackly. I can receive with no problem with the engine running and transmit crystal clear with the engine off.<br /><br />Can anyone give me any pointers as to how to fix this?<br /><br />Thanks<br /><br />Lol
 

rons boat

Petty Officer 1st Class
Joined
Dec 28, 2002
Messages
210
Re: Problems transmitting on VHF with engine running

Usually the receive side is affected more than is xmt. So we have a big clue to your problem. Make sure your transciever is connected directly to the battery with big enough conductiors that there will not be a voltage drop. Use 16 ga or better for power runs over 5 feet and make sure all connections are solid. You should check to see if the Voltage drops appreciable at the back of the transceiver during transmit. No more than a couple of tenths is acceptable. Antennas arn't usually affected by motor ignition noise on transmit unless there is some crazy loose connection in the antenna that is being modulated by engine vibration. I have limited my suggestion to power induced noise since that is most common. Even a bad battery can cause noise modualtion. A bad connection at the battery would keep the battery from being its normally low impedance shunt(filter) to noise.
 

Reel Appeal

Chief Petty Officer
Joined
Aug 19, 2002
Messages
566
Re: Problems transmitting on VHF with engine running

Lol,<br /> Make sure the spark plugs in your Johnson are of the "resistor" type.Non-resistor sparkplugs can and will cause radio interference.If the noise speeds up with the motor speed,then this is likely.Resistor type plugs suppress the RF interference normally generated by sparkplugs. ;) Resistor plugs(champion) may start with a "Q" in the plug number.
 

Boatist

Rear Admiral
Joined
Apr 22, 2002
Messages
4,552
Re: Problems transmitting on VHF with engine running

Lol<br />Good question and please come back and tell us all what the cure is. You have got a lot of good ideas already but I will add a couple.<br /><br />First I would like to know what type antenna you have, Brand, Model and DB Gain if you know?? Also where antenna is mounted, near motor or up front??<br /><br />Second is transmitter bad if sitting still with motor running or only if moving??<br /><br />Third if you turn your squelch off where reciver opens with no signal can you here the noise??<br /><br />You could have a broken wire in your Antenna or coax on the way to the antenna coax connection to the back of radio. When your stopped works ok but when have vibration and moving wire will make and break. Very common in small lite antennas that flex alot like a shake 497. If it is a 6DB or more antenna then antenna need to be straight up when moving.<br /><br />Can be getting noise from Alternator, Spark plugs and wires, or Tac signal. Do Power wires for you radio run all the way back to your main battery Bus?? Do Power wires run right along side your tac wires??<br /><br />In general a poping noise that changes speed with engin speed normaly spark plugs or spark plugs wires. A siren noise that changes with engine speed is normaly alternator whine. Crakly and broken usually Antenna, Antenna Cable, Antenna connection at back of radio, broken wire where coax goes thru hull, or antenna angle. Frying sound usually water in cable or antenna
 
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