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Author Topic: ---how do you think about the "SWR"---  (Read 3840 times)
BH4RKH
Member

Posts: 18




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« on: March 02, 2010, 07:57:52 AM »

if the SWR is 3
is it bad for the rig?
do I need to use a auto-tuner?
I hope you can give some suggestions!!!

tks vy
de
BH4RKH
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N4UM
Member

Posts: 593




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« Reply #1 on: March 02, 2010, 08:42:36 AM »

If the SWR is 3:1 right at the output of the radio, most modern radios will reduce their output in order to protect the radio.  In this sense , it's not bad for the radio but it is "bad" in terms of the amount of power going into the transmission line to the antenna.  This can be corrected by placing a tuner (either automatic or non-automatic) at the output of the radio.  The radio then "sees" a 52 ohm load and is "happy" in the sense that it will operate at full output.

If the transmission line is quite long and lossy much of the power going into it will be lost in the form of heat - even of the SWR at the output of the radio is very low.  The solution is to match the impedance of the line to the antenna and/or to use transmission line having low losses (such as open wire line).  The loss of power in the transmission line in the form of heat has nothing to do with the SWR right at the output of the radio. It is a function of the SWR on the transmission line itself and the quality of the line

A tuner right at the output of the radio coupled with good quality (low loss) transmission line can be an efficient system even if the SWR on the line iself is high.

I don't know if that helps you but it's how I "think about SWR."
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AA4PB
Member

Posts: 14420




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« Reply #2 on: March 02, 2010, 09:43:49 AM »

To give better advise you need to tell us
1) What kind of antenna?
2) What type of coax (or other feed line)?
3) How long is the feed line?
4) What band or bands is this for?

As stated, a 3:1 SWR is too high for any but an old tube type radio. The best way to fix it depends on the answers to the above questions.
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Bob  AA4PB
Garrisonville, VA
BH4RKH
Member

Posts: 18




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« Reply #3 on: March 02, 2010, 04:42:28 PM »

my rig is IC-7200 and FT-857D
my ant is 730V-1
30 meters 50 -7 coaxial line.

i use a 6 meters  jackstay, 14,21,28 Mhz are all good, below SWR 1.5:1
but the 7 Mhz SWR is high 3:1

there are some steel structure below the jackstay, maybe it's the problem???
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WB5JEO
Member

Posts: 805




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« Reply #4 on: March 04, 2010, 07:02:48 AM »

I have not used or examined this antenna, but I assume it is a trapped dipole mounted as a "V." It is very like the Comet H-422. I suspect it is the same antenna with different brand names.

First, when you adjust for 40-meters, does the 40-meter SWR behave as you would expect? This cannot be a very broad bandwidth antenna, so resonance should change rapidly as you adjust it. Describe what happens to SWR on 40 as you adjust the antenna.  Is it lowest at one end of the adjustment range? Is it lowest somewhere in the middle range? Is it the same 3:1 at all adjustments? If you do not see a distinct response when you change the 40-meter adjustment, it will suggest something other than the antenna, assuming the traps have not been badly adjusted.

What kind of steel structure is below the antenna? A steel building, a steel roof, steel railing...? The manufacturer claims it is insensitive to height above ground and nearby structures. At best, that is a vague claim. It cannot be strictly true.

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KF4FM
Member

Posts: 8




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« Reply #5 on: March 05, 2010, 06:06:29 AM »

First!  I've been away from amateur radio for over 15 years, so there's a lot I forgot and a lot I never knew.

My rig and magnetic loop tuner box SWR reading while nearly flat when tuning on CW, bounces up and sown like the output power meter when broadcasting SSB.  Is that normal?

rig is a FT 1000 Mark V, antenna MFJ-1788.

Thanks,
Joe
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AA4PB
Member

Posts: 14420




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« Reply #6 on: March 05, 2010, 08:17:25 AM »

Yes, it's normal. The SWR reading is only meaningful when you are outputting a constant power as in CW key down or tune.
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Bob  AA4PB
Garrisonville, VA
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