VHF Radio Output

[ROBERTH]

Hey folks, I am very curious here and hoping somone on this site is an expert in VHF radio output.....

I have 2 ICOM VHF radios. I have the upgraded Shakespeare 8900 model antenna's that have the silver solder that is supposed to be better at performance, so feel I have a pretty good system.

In testing with the ART-3 tester, I get all tests passing and VSWR less than 1.4 on both.

However, the Watts check for the output shows both only putting out 19 Watts . Since the radios are advertised to put out 25 Watts, is this normal to put out 6 less Watts?

 

[ocnslr]

Check the voltage at the radio connections, both prior to and while transmitting. My guess is a lot of drop and lower than optimal voltage at the radio.

Our two fixed radios were wired with one from the house bank and one from the engine batteries. Both to Digital 529 antenna. Used same instrument as you and usually got full power out.

 

[ROBERTH]

Thanks ocnslr, I had rewired to the radio box a few years back with oversize wiring to handle all the new electronics. However, I just went out and did another retest to make sure no drop issue.

Results were only .2v drop when keying the mic. Running with charger on, was 13. 7v and unplugged and let batteries settle for a bit Then got 12.6v before keying the mic and 12.4ish when keying the mic.

I am at a loss why the 2 radios, with new high end antenna's and ICOM radios put out the same, but not reach 25w or even close. They do seem to perform well, but I just would like to see the 25w or understand if this is normal.

The ICOM's are different models and yet both are performing the same.

 

[ocnslr]

Well, it certainly isn’t a voltage problem.

No insult intended, but are you sure bottom switch is in the correct power off position?

It could be the device. Do you have a friend with a boat you can test on?

 

[ROBERTH]

No worries, I am up for anything to try. Do you mean the ART-3 setting?

 

[Capt Bill]

The final output stage of the transmitter is designed to reduce power as SWR goes up (to protect the final amplifier). While 1.4:1 is not a bad SWR, it is not a perfect match (1:1 is), so I would expect some reduction in output. Remember that as SWR increases, the reflected power (wasted power reflected back to the transmitter) is going to increase as well, so therefore output will be reduced.

I think your radios are performing properly, and just FYI, each doubling of output power will only result in a 3db increase in signal strength, so even if your transmitter was outputting 25 watts as compared to 19 watts, your signal at the received end will only increase be about 3/4 of 1 decibel, really not even noticeable to the listening party.

 

[ROBERTH]

Thanks Captain Bill! So basically, I am not losing range due to the lesser watts output? That was my main concern really here.

 

[Capt Bill]

ROBERTH,

I really don't think your range will be affected, unless the conditions were such that your 19 watt transmitter was so far down in the noise floor, that the transmission was "not quite intelligible", and 3/4 db increase in signal would make it "just barely intelligible". But I think or all practical purposes, it will not make a difference.

On the subject of improving range, the very best thing anyone can do to improve copy is to improve their antenna, as practicable as they can. As a ham radio op for more than 60 years, I can tell you that without doubt. I have "worked" other VHF stations on the ham bands, at great distances, with only 1 watt of power, fed to a multi-element, high-gain antenna mounted 80' AGL, and had solid copy. It isn't the power; it's the height and the antenna.

In your case, you have done most of what can be done, if not all. You really can't increase your antenna height since it's mounted probably in the best spot it can be. The coast guard stations have towers, and are located very near shore, so they have the ability to hear transmission much farther than we can hear boat to boat.

 

[ROBERTH]

Thanks Cap!