Question about Garmin VHF-725 2-Way Radio

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VHF transmit power

I have a VHF marine radio with 25W of transmit power. When I connect an SWR meter and key the mic the meter reads 16 to 18W. Is this typical or does it indicate a problem with the radio? Thanks.

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Thank you for the info...very helpful! I guess the real test is if I can be heard by my fishing buddies. Thanks again.

Posted on Oct 05, 2007

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Hi, It is not typical but neither is there a problem with the radio. Transmit Power output is loosely dependent on the: 1. Frequency or channel you are transmitting. Normally, Marine Band VHF are calibrated for max (25 in your radio) at Ch16 or 156.800Mhz; 2. If the SWR of the antenna is not a flat 1.0, power tends to go down; 3. After some time, the TX side of the radio needs to be re-calibrated; 4. Power Supply - some radios will push max output only when powered with 13.8 and tends to go down when used with 12 volts. Hope this be of some help/idea. Post back should you need additional information. Good luck and kind regards.

Posted on Oct 04, 2007

  • Louie  Role
    Louie Role Oct 05, 2007

    HI again,

    Understand and you're welcome,
    A few other things based on experience:
    1. Height is might, the higher the antenna position on the boat, the farther the reach;
    2. Marine VHF works on line of sight principle;
    3. A ground plane and/or a ground strap from the grounded base connector of the antenna and radio to the engine and negative terminal of the battery connector improves performance;
    4. Metal rod antennas work better than fiberglass antennas (but of course prone to rusting);
    5. Having a common ground strap for all your electronics (GPS, fish/depth finder, loran) also improves performance and lessen interference.

    Tight lines.



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Most problems with radios that receive but do not transmit are antenna or antenna wire/connector issues. It's easy to receive with a marginal antenna but transmitting requires a good working antenna. If you have a SWR meter or can get your hands on one, install it in line with the antenna and test for reflected power. Of course, make sure your TX light comes on when you depress the mic switch. If not, switch mic and try again.
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Can this SWR be accurately be used for a boat VHF radio antenna? I have tied it and it seem to work but do not know if the reading are good.

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1st. You cannot "set" the swr. The swr is not set on the radio. The antenna must tuned to attain an appropriate SWR reading.

2nd, If this doesn't solve your problem then you could have a worse problem. If there is a problem with the mic such as a break in one of the wires, the radio's receive will be off until you put a good mic on it. Try a different mic, and see if the receive comes back. Then check and see if your transmitting better.

As well, your meter could just be bad, as well your coax or antenna. Your receive could be poor if the antenna is not tuned to lowest SWR.

If it has been working up till recently, and you have "set" the SWR on the radio, which is not what the SWR function is for, because you don't set SWR on the radio, you could have been using the radio with the SWR super high and blown the final or other sections of the radio out.

SWR is basically signal reflection. If the antenna is not the right length, it will reflect energy back into the radio and damage it over time. The more an antenna is off from the correct length, the more reflect you will get.

The meter in the radio is used to determine how much reflect you are getting. You ideally want to have the lowest SWR possible.

To check the SWR, you set the meter switch to CAL. Key the mic. while holding the mic key down, turn the CAL knob up until the needle is at the little triangle at the top right of the meter marked by "CAL", Then while still holding the key, flip the meter switch to SWR. where ever the needle is at that point is your SWR.

You want ch 20 to have the lowest SWR. If the swr reading on channel 40 is higher then channel 1 then your antenna is too long. if it is higher on 1 then 40, its too short. Make small adjustments until 1 has almost the same reading as 40. then check ch 20 and it should be real low.

As I have said, if you haven't tuned your antenna as I have just explained, and have been using it as is, the possibility is high that you have already hurt the radio.

Although it could also have a bad meter. Use an external meter to read the SWR.

Other things to check. Make sure cable connections are tight. Make sure coax is not damaged. try another antenna.

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I say system because your vehicle, antenna and coaxial cable are all part of this system. When you have a high reading and have to trim you antenna this is really calibrating the antenna to the vehicles body which acts as a ground plane.

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Connex 3300hp radio


Based on your post/description:

1. how do i set the swr
Normally SWR are calibrated on your operating channel (where you usually stand-by). This is to maximize transmit power and receive sensitivity. To set SWR, switch to channel of your choice, switch SWR control to CAL, key or press PTT, while pressing PTT rotate ADJ knob until max deflection of needle on meter, release mic, switch control to SWR, key/press PTT, needle reading/deflection is SWR for that channel.

I would suspect that your SWR will vary from your current 1.4. This is because you have too big excursion of channels (240 channels).

2.reading a 1.4
This reading is good enough and should do. However as earlier stated, you seem to have 240 channels which would mean that your radio + antenna moves in a wide bandwidth and since the antenna tuning is affected by frequency, your SWR will also be affected by channel.

Best if you can further lower it down.

3. some cb cant get me
This is because the standard CB radio is only 40 channels. The next would be a 80 channel and then 120 channels.

4. is it my radio
Yes, you have a wide coverage radio almost an extended 10 meter rig.

5. do i have to set my radio on high or low to set my swr
I will assume you are referring to power output, set it to HIGH when doing SWR calibration

Hope this be of some help/idea. Pls post back how things turned up or should you need additional information.

Good luck and kind regards.

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