View Full Version : SWR meter
08-01-2003, 02:31 AM
I am not eager to damage my new transciever once I get it so I am trying to learn some stuff on SWR and Antennas. #A have an older Micronta 3 range power/Modulation/SWR tester. #I am confused as to how to read the SWR meter. #It goes from 1 to 3 then where 4 should be it says SET there is also a red area between 3 and SET. #I take it that I am supposed to wire this inline between my transciever and antenna and turn the knob under SWR until it is on SET? Correctly me if I am wrong. #Thanks
08-01-2003, 02:54 AM
First be sure the meter is rated for the band you are working in.
Flip the switch to FWD, and calibrate to full scale, then flip to REV.
The foward reading is the "1" in the result, the reverse reading is what is being reflected back.
If it is under 2:1, you are ok, but if approaching that, you need to do some tuning on the antenna..
Make sure to check the bottom, middle, and top of the band.
Low at the bottom, high at the top, you are too long, vice versa, too short. Dip in the center, leave it, it's as good as it gets.
But, if it is higher than 2:1 at any point, revisit the antenna..
08-01-2003, 02:57 AM
Without seeing a picture of the meter, this is just a guess. Does it look like this?
If so, you key your rig in CW or FM mode with the meter set to read forward power and adjust until the meter reads to the far right, where it probably says SET. Then switch to reflected power, key the rig again and read the SWR.
However, before you trust it, that particular meter shown is only made for use up to 30 MHz, so using it on VHF/UHF will be at your own risk. It may indicate SWR OK and it may not.
If you have the Radio Shack number, they probably have the operating instructions on line. http://www.radioshack.com/prodsup....Ftest=1 (http://www.radioshack.com/prodsupport/productsupport.asp?cookie%5Ftest=1)
08-01-2003, 03:06 AM
I forgot to mention.
Always use your lowest power setting when checking SWR. If it is 4:1, and you are on high power, you are going to be looking for transistors shortly..
73, and keep learning http://www.qrz.com/iB_html/non-cgi/emoticons/smile.gif
08-01-2003, 03:11 AM
the cat no. on it is 21-522. and the switch for the SWR meter says SWR or CAL, there is no FWD or REV. Also how does one tune an antenna
OK, the CAL setting is for forward power - apply RF, and tune the dial on the front until the meter reads full (I believe it's most likely the SET line). Then remove the RF, move the switch to the SWR setting, and re-apply RF. Note you can't do this in SSB mode, you need something that will apply carrier (FM, AM, or CW).
Also, most of the Radio Shack meters I've ever seen were designed for CB use, meaning they're only good to 30 MHz, and are only rated for about 25 or so watts out. This means they're great for measuring SWR for a QRP radio, or perhaps a 2m mobile, but worthless for just about any other application. I have one of these myself, and I only use it for measuring SWR on my HTX-10. I have a separate SWR meter for 2m, and when I get back on HF full time, I'll get something like a MFJ Cross-needle tuner for most work.
08-01-2003, 03:35 AM
My guess is that CAL is the same as Forward power and SWR is the same as Reverse. Although it may not be exactly the same, try this link http://www.radioshack.com/ProdSup....7&T=htm (http://www.radioshack.com/ProdSupport/DocumentDetail/DocumentDetailIndex.asp?P=support_electronics&D=15777&T=htm)
As to adjusting the antenna, it depends on what type you have. Most likely you adjust the length slightly. Shorter to make it resonate higher in frequency and vice versa.
08-01-2003, 03:37 AM
Tuning the antenna? Depends on the antenna.
You working on the groundplane, or something else?
08-01-2003, 04:40 AM
Yes when I said how to tune a antenna, I meant the ground plain that I was building.
and the transciever I'm getting has a max output of 25 watts so I think I'll be ok with that meter... I hope http://www.qrz.com/iB_html/non-cgi/emoticons/confused.gif
08-01-2003, 08:32 AM
The swr depends on the size of the antenna. The elements of the antenna have to be the correct size for the frequency you are using. That's how one tunes a groundplane such as you're building. By making the sure vertical element and the ground radials are the correct size.
As for your meter, the 25 watts you will use is not the issue. The issue is the frequency. Most of those economy SWR meters are made for CB. CB is at 27 MHz. 2 meters is 144-148 MHz. What works on CB may not work on VHF as was pointed out above. If the swr meter is not acceptable for 2m and you use it anyway, you risk having very erroneous readings, which could either make you believe things are worse than they really are, or that things are fine while your rig is burning itself up.
Whether or not your particular swr meter is acceptable for VHF is something you need to determine. Looking at the Radio Shack web page, I did not find yours listed. If you can't find that info either, I'd say you are risking catastrophic failure of your rig if you trust your meter. MOST economy meters are NOT acceptable at VHF.
08-01-2003, 09:00 AM
Does anyone happen to know the length the elements should be in the ground plain attena for the 2 meter band. #
I hear it should be 19 inches for the center radial, and about 19 1/4 inches for the four radials.. If I build it to these specification do I still need to test SWR??
Also when I do tune it with the SWR guage, do I remove it when I start ragchewing or do I leave it inline. Thanks
08-01-2003, 09:25 AM
You determine Groundplane lenght by
Ex: 234/146 = 1.6 feet
To convert to Inches multiply by 12
And If I remember correctly (N0PU,STH, etc please confirm) the Radials (those elements that bend down at a 45 degree angle) should be 5% longer....
1/4 wave Formula is 234/freq (this is easy to remember)
also If I remember correctly 248(velocityFactor)/Freq can be used.....
>>>> Note: Dont stress out too much about the SWR and stuff for the longest time I would Just Trim Off 19.5 inches of RG-58 (leaving The Center Conductor), Place my new "antenna" where it wouldnt touch anything and would get on the air (I could kinda tell if my SWR was bad when antenna proformance would degrade) but ofcourse it is always good to check your SWR so to answer your question: Yes, you got the meter why not take a peek at your SWR just to make sure<<<<
# # # # # # # # # # # # # # # # # # # # # # # # # # # # #
# # # # # # # # # # #
# # # # # # # # # # # # # # # # # # # # # # # -KD7LDH
Lotsa good advise here. I use a Micronta CB meter in my camper on 2-meters. Since SWR is a RATIO, it works ok at that freq. An actual power meter might not.
I fried some resistors cause I forgot about the 50watts of power. After replacing with larger resistors it works fine.
Yes, leave it in the line in case something happens to the antenna.
Send your mail address (and list it on QRZ) and I will send you a scanned page showing the construction of a sloping ground plane. These have a better match and lower radiation angle than the horizontal ground plane.
TOM K8ERV email@example.com
You'd be better off to use a SWR meter that was
designed for the 2 meter band. If you don't have one,
Radio Shack did carry them because a friend of mine
purchased one from them a little while back. I use a
MFJ-259B antenna analizer. If your going to be messing
around with 2 meters only , then buying the meter from
Radio Shack would be all you'll need but, if you're an
antenna nut that likes to build and experiment on
different kinds of antennas, you should think about
investing in the MFJ-259B or if you think you may work
with some UHF antennas too , you'll need the MFJ-269B.
The old CB meters like those are questionable and
I wouldn't trust it with my expensive Ham equipment.