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N4NDX
03-04-2008, 02:07 AM
I`m curious to know how to tune my mobile antenna properly since is my first ham radio. I used to do it on Cb/ SSB radios but do not want to take a risk on my new rig since is a 65 watts out the box and don`t know if I need a dummy load or not to do it with.

Any input will be greatly appreciated.......

K9FV
03-04-2008, 02:21 AM
Well, since you are a new ham and have experience with tuning up radios on 11 meters, that knowledge is pretty good for ham radio also.... Set your radio to low power, perhaps 1 or 5 watts?

Then place your SWR meter - while it would be nice to have a "real" VHF SWR meter, your old CB style antenna will suffice to give a general indication of SWR.

Do it the same as for 11 meters - while it maybe not be "exact" - it will get you in the ball park. Just tune for min SWR. Then "IF" the radio works, it will most likely be ok. Modern VHF (and HF) radios will cut back on power to protect in case of high SWR.

Good luck and have fun,

73 de Ken H.

KA0GKT
03-04-2008, 02:28 AM
A dummy load doesn't do you any good as it is hooked up instead of your antenna to provide a proper impedance termination for RF power and other measurments.

Tuning an antenna for 2-meters is quite similar to tuning an 11-meter (CB)antenna; however VSWR (Voltage Standing Wave Ratio) meters which work at 27 MHz often are not accurate at 146 MHz. You should purchase or borrow a VSWR meter which will work at VHF frequencies to make your measurments.

There are many methods which you can use to tune your antenna. My favorite is to check teh VSWR at the top of the band and at the bottom of the band. If the measured VSWR is greater at the top than at the bottom, the antenna is too long. If it is greater at the bottom than at the top, teh antenna is too short. I also check at the middle of the band as well (146.52 is close enough) the VSWR, if plotted on graph paper will look like a broad smile, lowest at the middle of the band and roughly equal at top and bottom.

In my case, I have access to a Vector Network Analyzer (VNA) which can graphically represent the VSWR on an LCD screen. I have used the VNA to tune my 2-meter antennas. A VHF antenna analyzer will also work.


Here are a couple of hints (sorry if you already know them) For whatever reason Hams say the letters SWR and don't say "SWERS", however you will hear many amateurs refer to VSWR as "VizWer", a term common in Broadcast Engineering circles...no rhyme nor reason. Unless you are taking multiple readings like on a TV transmitter, SWR and VSWR are not usually plural so there is no such thing as SWRs or VSWRs. To pluralize them (not that you would) quickly identifies you as a newbie.

Now, get out there and tune that antenna! (and study for your General. I think you'll find HF far more satisfying than 2-meters).

N4NDX
03-04-2008, 03:37 AM
Hi Ken
You just said the magic word when you said set it in low power, Did not think about that, that was my major concern thinking of the max power . I`m going to try it that way as I used to with my AM`s but never the less keep in mind what ka0gkt said about the vswr meter. I`m going for my 2nd time club meeting tomorrow and see if some club member has one just in case the one I have does not work properly. Thanks

Well, since you are a new ham and have experience with tuning up radios on 11 meters, that knowledge is pretty good for ham radio also.... Set your radio to low power, perhaps 1 or 5 watts?


Then place your SWR meter - while it would be nice to have a "real" VHF SWR meter, your old CB style antenna will suffice to give a general indication of SWR.

Do it the same as for 11 meters - while it maybe not be "exact" - it will get you in the ball park. Just tune for min SWR. Then "IF" the radio works, it will most likely be ok. Modern VHF (and HF) radios will cut back on power to protect in case of high SWR.

Good luck and have fun,

73 de Ken H.

N4NDX
03-04-2008, 03:45 AM
Hi Steve

I`m going for my 2nd time club meeting tomorrow and see if some at the club has a vswr meter just in case the one I have does not work properly. Thanks
And yes I`m already studing for the General, I`ve heard is more fun and you get out farther.......

Well, since you are a new ham and have experience with tuning up radios on 11 meters, that knowledge is pretty good for ham radio also.... Set your radio to low power, perhaps 1 or 5 watts?

Then place your SWR meter - while it would be nice to have a "real" VHF SWR meter, your old CB style antenna will suffice to give a general indication of SWR.

Do it the same as for 11 meters - while it maybe not be "exact" - it will get you in the ball park. Just tune for min SWR. Then "IF" the radio works, it will most likely be ok. Modern VHF (and HF) radios will cut back on power to protect in case of high SWR.

Good luck and have fun,

73 de Ken H.


A dummy load doesn't do you any good as it is hooked up instead of your antenna to provide a proper impedance termination for RF power and other measurments.

Tuning an antenna for 2-meters is quite similar to tuning an 11-meter (CB)antenna; however VSWR (Voltage Standing Wave Ratio) meters which work at 27 MHz often are not accurate at 146 MHz. You should purchase or borrow a VSWR meter which will work at VHF frequencies to make your measurments.

There are many methods which you can use to tune your antenna. My favorite is to check teh VSWR at the top of the band and at the bottom of the band. If the measured VSWR is greater at the top than at the bottom, the antenna is too long. If it is greater at the bottom than at the top, teh antenna is too short. I also check at the middle of the band as well (146.52 is close enough) the VSWR, if plotted on graph paper will look like a broad smile, lowest at the middle of the band and roughly equal at top and bottom.

In my case, I have access to a Vector Network Analyzer (VNA) which can graphically represent the VSWR on an LCD screen. I have used the VNA to tune my 2-meter antennas. A VHF antenna analyzer will also work.


Here are a couple of hints (sorry if you already know them) For whatever reason Hams say the letters SWR and don't say "SWERS", however you will hear many amateurs refer to VSWR as "VizWer", a term common in Broadcast Engineering circles...no rhyme nor reason. Unless you are taking multiple readings like on a TV transmitter, SWR and VSWR are not usually plural so there is no such thing as SWRs or VSWRs. To pluralize them (not that you would) quickly identifies you as a newbie.

Now, get out there and tune that antenna! (and study for your General. I think you'll find HF far more satisfying than 2-meters).

W7LPN
03-04-2008, 04:56 AM
Make sure you are well grounded & cut very smal pieces off the whi0p. You can't put it back on, but you can, in most cases slide the whip up & down a bit to fine tune, just like CB SSB. :D

KB3LIX
03-04-2008, 05:31 AM
Don't forget to identify your transmissions.

KG6YTZ
03-04-2008, 05:56 AM
Yep. All of the above. :) Nothing special about the procedure. Check the bottom of the band, then check the top of the band [keeping in mind the CW-only segment from 144.0 to 144.1, per Part 97!]. If the reading is higher at the top of the band, the antenna is too long [more resonant at lower frequencies; shorten it to raise resonance]. If it's higher at the bottom of the band, the antenna is too short [more resonant at higher frequencies; lengthen it to lower resonance].

At 1/4-wavelength in free space [246/f], the difference between 144 MHz and 148 MHz is only about 0.55 inches. However, the coax, the mount, and the whip are obviously not "free space," so signals travel a tiny bit slower through them [this is called the velocity factor], which makes the difference a bit smaller, closer to about 0.52 inches [assuming a 95% velocity factor, 234/f]. At any rate, for a quarter-wavelength, there's only a bit more than half an inch difference between the band edges. Trim in SMALL amounts.

Actually, trim only if absolutely necessary. If your antenna has an adjustable whip with a set-screw, use that instead, and trim only if you have to. Trimming may be necessary if, for instance, you add a spring or a quick-disconnect to the base of the antenna.

You probably won't be able to achieve that elusive, mythical "flat match across the band" without a tuner [now guess why VHF/UHF tuners are both uncommon and unnecessary!], and you shouldn't knock yourself out trying to get a perfect 1:1. As long as the SWR is not too high - i.e., high enough to damage the rig - "As good as possible" is usually good enough, especially if it's anywhere under 2:1. Here's an informative PDF document (http://www.arrl.org/tis/info/pdf/q1106037.pdf) from the ARRL for further reading.

K7JEM
03-04-2008, 06:13 AM
One very important thing that no-one brought out:

You can tune an antenna, but you can't tune a fish.

W6TMI
03-04-2008, 07:37 AM
One very important thing that no-one brought out:

You can tune an antenna, but you can't tune a fish.

Ba da bum!
<Smack>
:p

KG6YTZ
03-04-2008, 08:12 AM
You can tune an antenna, but you can't tune a fish.
No, but you can teach it to play scales. :D