Posted: 1/27/2011 2:59:51 PM EDT
|
I picked up a radio and want to check the swr but don't know which needle or scale to look at on the gauge. Here is a fuzzy picture of me transmitting on 2M at 20 watts. I assume the power is on the left since it measures close to 20 watts but is the right side for swr?  |
|
this is called a "cross needle meter". one meter movement measures the forward power; the other meter movement measures the reflected power. ideally, there is no reflected power –– this is the optimum solution and represents a 1:1 SWR. the meter manufacturer has put some SWR lines in the middle; this is where you read the SWR. tell us what you had the switches set to on the meter. i ask because it does not look good from an SWR perspective. what are you driving, antenna-wise? ar-jedi |
|
Yaesu 350 into a Comet SBB5 mounted on top of a tire carrier on a jeep. The rear glass was up and the tail gate was open (I know, not ideal to check) but the radio is mounted in the back of the jeep and this was the easiest way. The meter is set on 144 on the 30 watt range. I just checked 440 and the left needle is over the 1.5 on the swr scale. |
|
Just noticed the little range on the meter, .1 for low and 1 for high. I switched the transmitter to 50 watts so I could use the high range on the meter and found that on 2m I have 2.5 and on 440 I have 1.5. Also saw in the manual that the swr is read where both needles cross. |
| Measure the SWR at the top and bottom of 2m. 145.000 on the bottom and 147.900 at the top. If the SWR is lower at 145.000 than 147.900, the whip needs shortened. The reverse is true it the SWR favors 147.900, the whip would need lengthened. The SBB5 has set screws where the whip goes into the base. Normally these antennas need no adjustment. But us Jeepers that have limited mounting options may benifit from tweaking it a bit. The goal is to make the SWR even on each end of the band with the lowest SWR in the middle of the band. |
|
Trying to read the low side of those scales, but it looks like you have a little under 4 watts forward power, and what looks like 0.9 watts reflected power. SWR is very high. With something approaching a reasonable SWR, the forward and reverse needles will cross and where they cross relative to those red curves at the bottom center tells you what the SWR is.
You have some sort of problem to have an SWR that high with a pretuned type antenna. |
|
Quoted:
The roof is not metal. The antenna is mounted to a piece of angle iron mounted to the cast aluminum tire carrier. Wood there be any benefit to running a wire from the mount to ground? Maybe the contact between the angle iron and tire mount are not good enough. Maybe the paint on the angle. and antenna. Try scraping it off and see. Maybe get a aluminum angle and weld it to the tire bracket. First try it somewhere else to check the antenna itself. Do you have an old piece of metal 18x18 or so you could drill a hole in. You could use a cookie sheet too. |
|
The 2m readings look good to me. The 440 is a tad high, but you may be getting some reflection off the rear window defogger element in the glass. You may just have to live with it unless you move the antenna (barring any grounding issues).
I have a 2003 Wrangler with a SBB5 mounted to the top of the windshield frame on the passenger side. I had to drill holes in the frame for the bracket, but I'm not shy when it comes to drilling holes in my vehicles. 
|
|
When I had my Jeep 06 LJ Rubicon I ran a ground wire from the antenna bracket to the frame.
At the engine compartment I ran a new ground from the battery to the frame. Ran the power supply from the battery to the radio including the ground. Make sure the antenna has a good contact to the metal bracket (remove any paint or rust and a little electric compound around the hole and ground connections goes a long way - antioxidant). |