| Author |
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Dxuall
| | Posted on Thursday, May 08, 2003 - 6:53 pm: | 
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what the problem can be? when i talk local or skip on hihg freq. the other stations tell me that i sound much louder on lower freq. (i have changed freq. from lower to higher or higher to lower with the same station in the same skip or local contact.) maybe the antenna length? need help please. ( radio-antenna swr is 1.0 high or low freq. 30ft. high) radio:galaxy 2547 @ 40 watts, antenna: skylab what is the right length between the base of the antenna and the tip? thank you for your comments. |
Barracuda
| | Posted on Thursday, May 08, 2003 - 9:12 pm: |
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Dxuall,
I'm no expert, and I can't answer your primary question, but based I what I believe I know, if you're getting 1.0:1 across the freq band with the skylab, go up that 30ft mast and measure the lenght of the antenna and tell us what the proper length is, because you got it perfect!
Barracuda |
de
| | Posted on Thursday, May 08, 2003 - 9:31 pm: |
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The problem is your meter. There is no such thing as a perfect 1:1 in real life. If you get a 1.2 you are about as perfect as you are going to get.
Put another meter in line and recheck. Put the meter in front of/before the amp. |
bruce
| | Posted on Thursday, May 08, 2003 - 10:11 pm: |
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my guess background noise |
Tech833
| | Posted on Friday, May 09, 2003 - 9:06 pm: |
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Your radio is not properly tuned.
This is a common problem in Amplitude Modulated wide band radios (like aircraft). The radio's tank circuit has to be tuned using a tracking generator set to sweep the intended frequency range of use. Then, and only then, will you be able to achieve the same performance at each end of your operating range.
Typically, for CB the frequency range is so narrow, this should not be a problem. |
Dxuall
| | Posted on Monday, May 12, 2003 - 12:01 pm: |
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thank you for your comments. what i tried to say and i forgot to write is i'am using a antenna matcher and i get 1.0 swr all across the band by adjusting the knobs. (antenna matcher: para dynamics pdc30 from copper) are antenna matchers good any ways?? I'am not using a amp. 40 watts is just the radio power. still need help!! radio set up: gal. base 2547 - 2ft. jumper rg8/u to ant. matcher - 40ft. coax rg8/u to skylab. here is some of the freq. swr readings without ant. match. that i can get with these radio and another diferent meter. 26.693.0 = 1.1 ,27.000.0 = 1.1,27.330.0 = 1.2, 27.645.0 = 1.3, 27.965.0 = 1.2 any more suggestions? |
de
| | Posted on Tuesday, May 13, 2003 - 12:15 am: |
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Re Dx...
Well there is your problem. Put your SWR meter before the tuner. This will give you the real SWR for the antenna.
Remember that an antenna tuner does not change the antenna nor does it physically tune an antenna--to tune an antenna you have to adjust elemental length, gamma match, etc. All an antenna tuner does is to allow the radio to see 50 ohms at some point along the coax--to keep the radio happy. So if you have a reading on your SWR meter of 2:1 without a tuner and you tuner it down to 1:1 your antennas SWR is still 2:1 but your radio is seeing an acceptable 50 ohm load. The efficiency of your antenna is not altered by the insertion of a tuner and its true SWR remains the same.
An antenna that is too long before a tuner is still tool long after a tuner. Take the tuner out of line entirely. Set your radio to where you speak the most. Physically tune/prune/adjust the antenna itself to get the lowest possibel SWR at that point. Consult the manufacturer for adjustment procedures. How far away from this ideal center you can go without excessive SWR is dependant on the band width of the antenna itself.
Personal advise from someone who uses single band antennas extensively. Take the time to adjust and or trim the antenna. Physically tune the antenna itself per the manufacturers directions. Use the tuner for those multiband antennas where you have to trick your radio into seeing a 50 ohm load--such as multi band antennas with variable impedances based on band and band width. |
Dxuall
| | Posted on Tuesday, May 13, 2003 - 5:10 pm: |
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thank you for the comments i really appreciate them. Does anybody know where can i find information or a web site to get measurements on the skylab? so i can trim the antenna. how much should i cut 1",3/4",1/2,1/4" at the time??. |
de
| | Posted on Thursday, May 15, 2003 - 12:33 am: |
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Re Dx....
Have a seat and make yourself comfortable.
The first thing you want to do is find out if you need to lengthen or shorten the antenna. Take the tuner out of line. And check the SWR without the tuner at the following points:lowest frequency, highest frequency, middle frequency and one or two points between the middle frequency AND the lowest and the highest. Make note of the readings. Always reset your meter for each reading and use the same power output.
Where is the reading the lowest? Here is the reason for all this testing. If you get the lowest SWR on the the direction of the highest frequency the antenna is too short. If you get the lowest SWR in the direction of the lowest frequency the antenna is too long.
The formula for a Dipole Antenna 468/Freq in Mhz. The lower the frequency the longer the length of wire to get resonance. The higher the frequency the shorter the length of wire to get resonence. Make note of where the antenna is best tuned and change the length slowly in the direction that will bring the comfort length to where you want to talk/will talk the most.
Remember if you have to cut anything always cut in small bites of 1/8 in. You cannot reglue the pieces together once you cut. If you have to cut move slowly and take your time.
IF ON THE OTHER HAND, you have cut off too much all is not lost. You can use those split bolt connectors used by electricians and brass welding rods to lengthen a whip. OR if the element is tube type just get a piece of aluminum pipe to fit into the existing tube. Cut a few slots at the end of the bigger tube. Insert a new section of aluminum tube inside the larger section and clamp down to secure using stainess pipe claps from the hardware store.
Take your time. Be patient.
DE |
Dxuall
| | Posted on Thursday, May 15, 2003 - 1:34 pm: |
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ok thank you De. i'am going to try that "formula" low swr on high f. = too short whip and so forth. |
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