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Author Topic: HighvSWR on 70cm  (Read 2340 times)
KT4DLB
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Posts: 76




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« on: March 22, 2013, 09:31:21 AM »

I'm using a Diamond X-50 antenna for 2 meters and 70 cm. The SWR is ok on 2 meters but high on 70 cm. According to what I've read only the coax could be causing the problem as a short. But I have check the coax and plugs and everything is ok. Any suggestions?

73's

Lamar
KK4NZO
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W8JX
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« Reply #1 on: March 22, 2013, 12:07:22 PM »

How high is high?
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WB2WIK
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Posts: 20611




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« Reply #2 on: March 22, 2013, 03:18:20 PM »

How high is high?

Ditto.  How high is high?

Also, what are you using to measure the SWR?

And also, did you plot SWR vs. frequency across the 440 MHz band?  It's useful to have that data, recorded for reference, so you know how to adjust the antenna if it needs adjusting.
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KT4DLB
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Posts: 76




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« Reply #3 on: March 23, 2013, 12:30:48 PM »

I'm going by the meter on the FT-897D when keying the mic, it shows HSWR and according to the manual, thats above 3 on the scale. I'm new in ham radio and don't want to hurt the radio due to high swr. I don't have a swr meter that will read above 150 mhz. I have my eye on one that will read up to I believe 500 mhz but haven't had the money to buy it yet.

73's

Lamar
KK4NZO
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G8YMW
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Posts: 237




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« Reply #4 on: March 23, 2013, 01:46:51 PM »

Hi Lamar
I suggest using another SWR bridge and scan across the band, as has been suggested above.
The meter in the radio can be out (best to have several meters take readings, borrow some from your friends).


Good Luck
Tony
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73 details Tony
Sent by WW2 Royal Navy signal lamp
KT4DLB
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Posts: 76




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« Reply #5 on: March 23, 2013, 02:09:55 PM »

Ok will check into that then.
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K1CJS
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Posts: 6045




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« Reply #6 on: March 24, 2013, 07:20:18 AM »

Check if there is any sort of reflective surface next to the antenna too--especially the bottom of it.  Something that won't affect the SWR much on 2 meters may well prove to be a problem on 440.  One guy had a problem with SWR just as you do.  Turned out that his mast was a bit high for the space he had to mount the antenna, so he just moved the antenna down a bit--leaving just enough mast next to the antenna to affect the SWR.  When he cut the extra mast piece off, his SWR dropped to a comfortable level.

Also, the shorter the wavelength, the smaller the adjustment that has to be made.  Changing the adjustment (if the antenna is adjustable, that is) by a quarter of an inch may well push the SWR right past its ideal point to the other extreme.  That is one reason an antenna analyzer is a much better tool to adjust the antenna than an SWR meter is--especially for the higher frequencies. 
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KT4DLB
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Posts: 76




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« Reply #7 on: March 30, 2013, 08:49:47 AM »

I figure out what the problem was. I had 50 ft of coax running from the antenna to the house entry point at which I had about 6 foot that I rolled up and taped up. Once I undone the roll and just let it hang down from the window, SWR down to less than 1.5 on 2 meters and 70 cm meters, Thanks for all the info, I really appreicate it.


73's

Lamar
KK4NZO
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K1CJS
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« Reply #8 on: March 30, 2013, 10:27:04 AM »

Yup.  Just one of those things that only an actual 'look-see' could tell.  Glad you figured it out!  73!
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