| Author |
Message |
    
Killer
Junior Member
Username: Killer
Post Number: 17
Registered: 1-2007
| | Posted on Thursday, May 24, 2007 - 9:42 am: | 
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OK i used my 259B analyzer to setup the antenna in my mobile and it worked great.Now I'm trying to use it on my base setup and i have a small problem.My antenna is the SE Lighting 4+.I have two runs of coax coming from the antenna to the house.First i hooked my analyzer straight to the end of each V and H coax and set my SWRs.Both SWRs are a 1.2.The problem is when i hook the both coax to my switch box.I ran a jumper out of the box to my analyzer and I'm getting a totally different SWR reading on the analyzer now.So my question is,do i reset the SWRs to match the setup with the jumper in line or is the jumper causing a false reading.Quick response please.I'm kinda stuck here :-( |
Marconi
Advanced Member
Username: Marconi
Post Number: 716
Registered: 11-2001
| | Posted on Thursday, May 24, 2007 - 11:33 am: |
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How long is the jumper? It could be the switch box or it could be the jumper. I would say typically when you have a good reading in a setup and you add some small lenght of coax and it changes the readings then you do not have the antenna set as well as you think. Using long lines to tune an antenna like you have can be problematic even with an analyzer.
Do you have another antenna that you think is set OK that you can verify the jumper and SB against?
How long are you feed lines and what coax do you use? |
Tech237
Moderator
Username: Tech237
Post Number: 794
Registered: 4-2004
| | Posted on Thursday, May 24, 2007 - 5:01 pm: |
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ALWAYS setup your antennas in the format you intend to use them. That means with switchboxes, jumper cables, etc. Use multiples of an electrical halfwave of coax so that what you read in the shack is what is really at the antenna.
Simon
Tech237
KD7IEB
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Killer
Junior Member
Username: Killer
Post Number: 18
Registered: 1-2007
| | Posted on Thursday, May 24, 2007 - 7:42 pm: |
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I fixed it.My first mistake was that i was using a jumper that i already had (mini 8).I made a new jumper out of the same coax( CA-400) that i have ran to the antenna.I think my problem was that the first jumper i was using had a different velocity factor.After i made a 1/4 wave length jumper out of the same coax it reads the same now through the switch or individually. |
Dale
Advanced Member
Username: Dale
Post Number: 892
Registered: 12-2002
| | Posted on Thursday, May 24, 2007 - 7:58 pm: |
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how ya measured 1/4 wave coax?
36ft.=1wave
18ft.=1/2wave
9ft.=1/4wave
is this theory correct
dale/a.k.a.hotrod
cef426
cvc#64
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Marconi
Advanced Member
Username: Marconi
Post Number: 718
Registered: 11-2001
| | Posted on Friday, May 25, 2007 - 7:06 pm: |
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Killer, I curious what kind of analyzer numbers for each polarity you are getting with the SE 4+ reading at the end of the jumper. |
Killer
Junior Member
Username: Killer
Post Number: 19
Registered: 1-2007
| | Posted on Friday, May 25, 2007 - 11:03 pm: |
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Do you mean my SWR's ,Marconi ? |
Dale
Advanced Member
Username: Dale
Post Number: 901
Registered: 12-2002
| | Posted on Saturday, May 26, 2007 - 9:25 am: |
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well ya got a good jumper with that ca400
what lenth is it
dale/a.k.a.hotrod
cef426
cvc#64
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Patzerozero
Senior Member
Username: Patzerozero
Post Number: 3750
Registered: 7-2004
| | Posted on Saturday, May 26, 2007 - 10:39 am: |
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killer, read R & X from the analyzer, & what freq does analyzer show lowest SWR on? that'll give an idea if the antenna actually IS tuned near 27.205 mHz, or if it's way off & something (coax maybe) is causing a false 'good' reading. |
Killer
Junior Member
Username: Killer
Post Number: 20
Registered: 1-2007
| | Posted on Saturday, May 26, 2007 - 11:06 am: |
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OK with the analyzer hooked to my jumper coming out of the switch box on Vertical and the frequency set at 27.205 it reads R=51 X=11 and the SWR is 1.2
On Horizontal it reads R=45 X=17 with an SWR of 1.4
OK with out the jumper or switch box.This is hooking straight to each run of coax leading to the antenna.
On Vertical it reads R=58 and x=3 with an SWR of 1.1
On Horizontal it reads R=68 X= 4 with and SWR of 1.3
I don't know anything about what any of this means so some help is appreciated. |
Marconi
Advanced Member
Username: Marconi
Post Number: 719
Registered: 11-2001
| | Posted on Saturday, May 26, 2007 - 12:30 pm: |
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Just as I suspected!
Killer, with an antenna like the SE 4+ it is basically setup to work with a center frequency in the CB band of 11 meters. Everything except the tuning is fixed and preset at the factory. They do give you a starting point, but that is just a starting point only.
You have to be confident that the wires are of the correct length, are all installed on the right elements of the antenna, and are all making good connections first-off. I suspect you already have that in hand.
Then fine-tuning is all that remains. I don't think you will find it advisable to use your working feed line as a tool in tuning. There are still too many variables, just with the tuner alone to use a long working feed line to tune such an antenna. If you were installing an Imax or A99, which are basically fixed and preset to tune by design, then you could get by, in most cases, using your working feed line to check the matching conditions at the feed point. It is possible to use an SWR meter to get a reasonable match that overcomes the environmentally affects, but this antenna can be more difficult and the SE design will make this very tedious to be correct.
A long working coax line, attached to a feed point with a totally unknown resistance and reactance, can act just like a impedance transformer. Such a transformation may well minimize any errors to the point of appearing to be an excellent match when none exist. For example with transformation you may see a condition with R=30 and X=28 on your analyzer and still see an SWR near to 1 to 1, when in fact your match is more like to be 3:1 SWR or more.
If you use an Analyzer, you need to use the information factors it is capable of providing in order to see the approximate condition at the feed point and not 100' back towards the radio. Any long length of coax that is terminated in a non-resistive load at the antenna can cause transformation at various points along the line. One possible test of this is to add some short length of additional coax to your system and see if your match changes.
SWR is probably the least likely consideration to be worried about at this point. You really need to be checking the resistive and reactive match as close to the feed point as possible, and pretty much rules out using long lines. That is why they make these analyzers portable.
You have to read your manual and try and understand some of what you are told. After you get the matching device set to reflect good conditions for reactance and resistance at the frequency you desire, then you can add your working feed line to your system and check things out. A typical good match at the feed point should be R=<>50, X=<>0, and SWR then should read <> 1.01 to 1 at the frequency you wish to use.
The tuner you have to work with is at least 18" long and the tap point for the center conductor of your coax has to almost be in the perfect location along that length in order for the conditions above to appear.
Understand that every site where this antenna is installed is different and height being another factor. These are factors in the tuning process that you must overcome when setting the proper tap point for a match. With this antenna it is possible to set one near the ground and then raise it up to installed height without really affecting the tune, but don't be surprised when this does not happen either. I recommend tuning at installed heights to be sure. Then use your analyzer to check your system at the transmitter end of the line, and see if the numbers are still close. If not, take readings starting at the radio end of the system and place your meter at the output side of the coax for every device in line till you get to the working feed line. Theoretically you should see numbers very close to those read at the antenna. If not then either the load is still wrong or the device or coax has a problem.
This may give you a clue as to what is going on. Don't look for the readings to exactly equal, but they should be very close.
Now tell us what your best readings for (R, X, SWR, frequency) are at the radio end of the line for the both sides of you SE 4+.
Good luck. You get this one right and you will probably love it when the DX starts. |
