| Author |
Message |
    
Itatorro
Junior Member
Username: Itatorro
Post Number: 35
Registered: 6-2005
| | Posted on Wednesday, June 22, 2005 - 8:43 pm: | 
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Problem: High VSWR when over 90w and up ...???
Without amp on and up to position 4 of the output level control on the amp my SWR is 1.25 across the band. Position 4 DK's approximately 73 watts. When I get to aprx. 90 DK and higher the SWR goes into strawberry land, 3:1+. Position 6 puts out about 120watts DK I don't really even think of using it.
I wonder where to start look for problems as I just ordered a TS DX500... I need to iron out the SWR before installation of my new Copper Tuned Magnum 257 and DX500HDV.
Current System:
Cobra75 WX ST 3w DK Swinging 5
8ft RG58 to
KL400 amp
13ft RG58 to
A-1700 six ft antenna. Antenna is rated to 2KW
Antenna is mounted on the rear door of my Jeep Unlimited.
You can see the mount here: http://www.arizonarockyroad.com/pages/1/index.htm
Thank you for you help. |
Bruce
Senior Member
Username: Bruce
Post Number: 2880
Registered: 9-2003
| | Posted on Wednesday, June 22, 2005 - 10:39 pm: |
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harmonic output go up and your meter reads that reflected power too remember a 54 meg signal will show up as a very high VSWR on a 10 meter antenna. |
Chad
Intermediate Member
Username: Chad
Post Number: 340
Registered: 11-2004
| | Posted on Thursday, June 23, 2005 - 8:41 am: |
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I vote harmonics too. Unfortunately you cannot lower the DK easily of the cobra 75, I suspect this will help.
I woulddn't do much to remedy the problem till you try the 257 and the new amp, I suspect the problem may go away.
I have also seen really cheapo coax break down at higher power. I would certainly use RG8X or better.
Chad |
Itatorro
Junior Member
Username: Itatorro
Post Number: 36
Registered: 6-2005
| | Posted on Thursday, June 23, 2005 - 1:31 pm: |
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I was thinking of RG8x mini but i think i was lookin at coax on Copper and they had a rating of 1kw for there rg58???... My cable is the FireStik branded 58 that they call FireFlex. I have only been using this set up for about 2 weeks and everthing is new. i realy don't suspect sinsulation break down ATT with the pwr that i am running. I use the Firestick Model K-4A stud mount also.
I discovered last night that with the DK set aprx 73w (Good SWR)that the SWR rises sharply with Modulation. I am sure that it's peaking over 90w
I will be going out to use a bird 43 to see what number i get and then plug them into my SpreadSheet and see what it says. I found a post that sounded just like my problem where the guy was using a RATshaack(RS) meter also. He accquired a DOSY ??? meter and it read fine. the only other thing that happened on that thread was other RS meter users said that theirs were giving good SWR at Higher power levels.
thanks for you interest and help gentle persons. |
Itatorro
Junior Member
Username: Itatorro
Post Number: 37
Registered: 6-2005
| | Posted on Thursday, June 23, 2005 - 2:13 pm: |
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ALL,
My last post hasn't appeared yet.
I failed to mention that I was using a Radio Shack meter in my initial post.
I took the Bird 43, I think it is averaging meter, out and did new measurements on the highest output of my amp.
Measurements are DK
105w forward and 1w reflected on Ch1
105w and 2w reflected on CH40
My Spreadsheet calculation says I have 1.21 and 1.31 respectively. Pretty Darn Good!
Hey! What is a good portable meter?
The RS meter appears to be close to Bird calculations at about 50w and lower.
thanks again.
it |
Chad
Intermediate Member
Username: Chad
Post Number: 344
Registered: 11-2004
| | Posted on Thursday, June 23, 2005 - 9:54 pm: |
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Know what? I had the same problem with SWR shooting up with a radio shack meter. Bought an astatic 600 and no problem. Just for grins try a different meter and please let me know I'm not insane  It would be just fine and just launch! |
Itatorro
Junior Member
Username: Itatorro
Post Number: 38
Registered: 6-2005
| | Posted on Monday, June 27, 2005 - 4:27 pm: |
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ATT I only have the bird43 and the RS. The RS meter when at low power agrees with the Bird..
Chad: How big is the Astatic 600?
thanks
it |
Tech808
Moderator
Username: Tech808
Post Number: 6192
Registered: 8-2002
| | Posted on Monday, June 27, 2005 - 5:08 pm: |
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Itatoro,
Specifications:
Freq. Range: 25-30 MHz
Impedance: 50 Ohms
Accuracy: SWR 10%; RF Power 7% on 0-10W, 10% on 100W and 5000W scales; Modulation 10%
Dimensions: 9.75"W x 4.35"D x 4.25"H
Lon
Tech808
CEF808
N9OSN
|
Crackerjack
Advanced Member
Username: Crackerjack
Post Number: 682
Registered: 7-2004
| | Posted on Monday, June 27, 2005 - 6:29 pm: |
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I am thinking that the coax is not good. It could be breaking down somewhere around 90W (whatever).
Choice 2 is that you used a mount that has an insuffucient insulator for that power. If the mount is weak, forget qhat the antenna ia rated for. |
