SWR meter Marine Vs. 2M amature...

[MrMoMo]

Ok, so at work I have an SWR meter designed for marine radios.

Marine radios operate between 156 - 157Mhz

2M amature operates 144 - 148 Mhz

How accurate would my marine band SWR meter be on my 2M antenna setup? (frequency is just over 5% out, would SWR be 5% out?)

Thanks!

 

[dfmorse]

Mo;

I would use it cuz it is close enough for what ur doing. Since u will be tuning for minimum SWR, it should be accurate enough for ham work.

Most ham 2m antennas and rigs are broad band enough to handle a 2:1 VSWR; although, u would like to see 1.5:1.

k0dar
...

 

[MrMoMo]

Cool thanks. I'll try it.

 

[MrMoMo]

Ok... here goes...

Last week when my licence arrived in the mail I transmitted on low power, hit the local repeater ~25km away and was told that my signal was great.

I hooked up my SWR meter tonight and "set" it. Then I TX and the needle PEGGED. This is not a good thing, as the middle of my scale is 3. If I set my meter to the "power" setting I seem to be transmitting at about 5W (radio set to 10W power level)

If I tune the "set" point all the way back the needle stays "in range" but I really don't want to be transmitting in a state like this.

My antenna is 19-1/8" long, it has RG58C/U coax with soldered on PL-259 connectors.

The reading that I got looks to me like a bad connector somewhere, but wouldn't that give me a very weak and poor signal - how could I have been coming in clear? Could it be that I am out of the marine band so my meter is innacurate by that much? I didn't burn out my radio!

Me is a bitsy confused at this point...........

Any thoughts?

 

[MrMoMo]

DOH!! I had my SWR meter inline backwards...

I have an SWR of 2.0:1 and am transmitting @ 20W (so I guess my antenna has a gian of 3dB?)

(hint to me in future... ANT and RADIO are different!!)

 

[ParadiseCruiser]

>> DOH!!

Bruce, I have so many of these in my collection that you cannot even imagine. You have a very long way to go to catch up...

>> so I guess my antenna has a gian of 3dB?

No. Gain is implicit in the design of the antenna. Whatever it is, it is by design. The transmitted power or SWR do not change that... however, these parameters combined with gain will change the Effective Radiated Power (ERP) that will actually radiate off your antenna.

R -

 

[MrMoMo]

Hmm, so my SWR meters power reading is innacurate, or my radio is more powerful than it states it is?

I also noticed that my SWR changes with different frequencies. Between 1.5:1 and 2:1. Is this normal or whacky? Also noticed that when my SWR is 1.5:1 my power was 11W not 20W

My SWR is designed for Marine VHF, and the top of the power scale is 30W. If I transmit on High power in SWR mode (not power mode) is it possible to damage the meter?

Thanks!

 

[brew8]

Why don't you go to the local radio shop and see if they have a BIRD wattmeter or a similar meter with a plug for your band, much better and then you would know where your at. They would proably check it for free, it would give you forward and reflected power and you can tune the antenna properly. Cheers, Larry

 

[ParadiseCruiser]

B -

>> I also noticed that my SWR changes with different frequencies... Is this normal or whacky?

Normal. SWR is a function of frequency: Change the frequency, the SWR changes with it, sometimes imperceptibly, others times quite significantly. Depends upon the circumstances.

SWR measures the ratio of forward power vs reflected power, so as the SWR changes, so does the forward power measured on a watt meter.

Larry's advice is good, but Bird meters are top-of-the-line precision instruments (very $$$). Not everyone has one sitting on the shelf to tune antennas.

In any case, these type of measurements are not a "do it once and you're good to go" affair. There are countless factors that can change antenna tuning, so it is something you need to check periodically just like any other PM on your truck.

Best advice is to loose the marine meter and get a quality power/SWR meter that is designed for the frequencies you will be using. It will be a valued investment that you will use frequently.

This "I just found this cool SWR meter on eBay for $10" stuff is nuts. Spend some time on the radio shop sites on the Internet, read the reviews, and generally do the homework. A proper meter alone will not help you. You need to understand what you are measuring. It will be time very well spent.

Cheers, R -

 

[MrMoMo]

I just brought my meter home from work to check if I was near, since I made the antenna myself I wanted to make sure I wasn't going to blow the radio up. I don't plan on using this one for my 2M stuff, just wanted a quick check.

At work it is a simple plug in to check the antenna is good, before handing a $1M+ boat over to the customer to find that they have no radio transmit-ability. Marine VHF operation is very critical in these boats as they are used in search and rescue, and are often equipped with a "distress" feature that is tied into the GPS, and transmits the location of the vessel. So.. I always do a quick check to make sure.