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Author Topic: SWR meter Placement  (Read 7166 times)
WH7PL
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Posts: 4




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« on: October 03, 2008, 05:45:43 AM »

If I am using a SWR Meter in conjunction with an antenna tuner, can I place the SWR meter between the antenna and the tuner in order to match the actual antenna SWR?
Because if I place the meter between the radio and the tuner, I am only getting the 'adjusted' SWR from the tuner right?


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W5JLF
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« Reply #1 on: October 03, 2008, 05:54:44 AM »

Yes you can.  That is how I have mine configured and I like the way it works.

Joe, W5JLF
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WG7X
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Posts: 350




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« Reply #2 on: October 03, 2008, 06:36:00 AM »

If you place the meter between the antenna and the tuner, all it will show is the actual match (SWR) at the antenna.

You cannot then use the tuner, which is before the meter, to "tune" the antenna.

The rig is looking into the tuner. That is the match that is important. It does not matter what mis-match is on the output side of the tuner, except where feedline losses are concerned.

The only reason for having a tuner in the first place it to use it to produce a reasonable match for the radio and then to transfer the power to the load. Why would you not place the meter between the radio and the input to the tuner?

This is the only place that you can get any usable information. The meter itself is designed to work best into a 50 ohm load as is the rig. Placing the meter anywhere else is just useless, because it's main duty is to inform the operator when there is a mis-match that needs to be corrected. Adjusting the tuner corrects the match and rig is working again. In order for this to happen, the meter needs to be placed in the correct place in the circuit (system) and that is after the radio but before the tuner.

Any other placement is wasted.

FWIW

Gary WG7X
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AD5X
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« Reply #3 on: October 03, 2008, 06:36:11 AM »

Think about this a little bit.  How could you possibly adjust the SWR with the tuner if the SWR meter is AFTER the tuner?  The SWR meter will only show the SWR of the antenna/feedline, and no adjustment of the tuner will result in a change in this indicated SWR.  The SWR meter must be before the tuner, so the reults of the tuner adjustments can be seen.  

Phil - AD5X
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K5DVW
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« Reply #4 on: October 03, 2008, 06:51:27 AM »

The adjusted VSWR is what you WANT to see. Why wouldnt it be?
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W5DXP
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« Reply #5 on: October 03, 2008, 07:38:13 AM »

> WG7X wrote: If you place the meter between the antenna and the tuner, all it will show is the actual match (SWR) at the antenna. You cannot then use the tuner, which is before the meter, to "tune" the antenna.

Yes, you can - with a dual-needle SWR meter - see below.

> AD5X wrote: Think about this a little bit. How could you possibly adjust the SWR with the tuner if the SWR meter is AFTER the tuner?

Think about it indeed. Even though the SWR is constant, you can tune the dual-needle SWR meter for maximum forward power and maximum reflected power. At that point the system is "tuned". This is akin to tuning the system for maximum radiated power.

Let's lay to rest the myth that a tuner has no effect between the tuner and the antenna.
--
73, Cecil, w5dxp.com
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
AD4U
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« Reply #6 on: October 03, 2008, 08:38:40 AM »

It depends.........

If you really want to adjust your antenna for minimum SWR, unhook the tuner and set it on the floor.  Put the SWR meter between the rig and the antenna.  You will get the best indication of actual SWR if the SWR meter is actually located right at the antenna and not in the shack.  But for real world use, that is really not necessary.  Coax losses will usually make the SWR in the shack look better than it really is at the antenna.

If you are trying to adjust your "tuner" to get minimum SWR at your rig in order to make your transmitter happy, then put the SWR meter between the rig and the "tuner". Tune the "tuner" for minimum SWR as indicated on the SWR meter.  This WILL NOT do anything to reduce the SWR between the "tuner" and the antenna.  It will only make your transmitter happy with the impedance it sees.

Dick  AD4U
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WA3SKN
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« Reply #7 on: October 03, 2008, 09:36:10 AM »

Question...
What are you trying to measure?
The meter measures VSWR relative to a 50 ohm impedance point.  Placed between the antenna and tuner, it will not be accurate if that point is not 50 ohms.  If it is 50 ohms you do not need a tuner.  Any adjustments made to the tuner will not show on the meter because the impedance point of the meter has not changed... so no need for the meter!
The object is to present a 50 ohm load to the transmitter so maximum power will be transferred to the antenna system.  Hopefully, the antenna system will radiate most of that power... and in a direction that is useful.  The tuner does not change the impedance of the antenna.
73

-Mike.
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AD5X
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« Reply #8 on: October 03, 2008, 09:42:23 AM »

W5DXP "AD5X wrote: Think about this a little bit. How could you possibly adjust the SWR with the tuner if the SWR meter is AFTER the tuner?

Think about it indeed. Even though the SWR is constant, you can tune the dual-needle SWR meter for maximum forward power and maximum reflected power. At that point the system is "tuned". This is akin to tuning the system for maximum radiated power.

Let's lay to rest the myth that a tuner has no effect between the tuner and the antenna."

Well, I agree with you Cecil.  But I assumed he was talking about measuring SWR (maybe not a good assumption) based on his question, not forward and reflected power.  If he can't figure out the best place to put an SWR meter and tuner for measuring SWR, I doubt if he can figure out that he needs to tune for maximum forward power and maximum reflected power on a dual-needle SWR meter if the SWR meter is after the tuner.

Phil - AD5X
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N4CQR
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« Reply #9 on: October 03, 2008, 09:48:14 AM »

Interesting variety of answers...

Here is a picture of how to hook your stuff up.

http://www.hamuniverse.com/tuner.html

Most manual tuners come with instructions of how to set your stuff up. Most transceivers has the same information in their manual(s) as does the VSWR meters.

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WB6BYU
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« Reply #10 on: October 03, 2008, 11:09:34 AM »

Yes, you CAN place the meter between the tuner and the
antenna.  At that point it will indicate the SWR on the
coax to the antenna.  You can then trim the ANTENNA for
minimum SWR.  This is the best approach for a coax-fed
antenna.

Adjusting the tuner may not be as easy:  if the SWR meter
is really a power meter, you can adjust the tuner for
maximum power output (since the SWR won't change.)  But
if your meter really reads SWR rather than power, this
won't work for adjusting the tuner.  I certainly know of
folks who adjust antennas for maximum power output (or
with some of the earlier solid state rigs, maximum
collector current) rather than SWR, since this finds the
point where the rig itself allows maximum output.  I had
to do this with one rig on 160m where my SWR meter wasn't
sensitive enough, and by the time I got the tuner adjusted
for maximum output I usually ended up blowing a fuse in
the power supply because the rig was drawing too much
current.

But generally, the SWR on the coax won't change as the
tuner is adjusted (except for some specific conditions
such as harmonic output from the transmitter) so the
best place to put the SWR meter is between the rig and
the tuner if you are going to use it to adjust the tuner.
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W5DXP
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« Reply #11 on: October 03, 2008, 11:43:53 AM »

> AD5X wrote: Well, I agree with you Cecil. But I assumed he was talking about measuring SWR (maybe not a good assumption) based on his question, not forward and reflected power.

Note that I did not respond to him (WH7PL) but instead responded to two extra class licensees, WG7X and you, who (apparently) didn't know the system could be tuned with the dual-needle SWR meter between the tuner and the antenna. You asked: "How could you possibly adjust the SWR with the tuner if the SWR meter is AFTER the tuner?" I simply answered your question based on a dual-needle SWR meter. I'm waging a crusade against the myth that the tuner accomplishes absolutely nothing between the tuner and the antenna.
--
73, Cecil, w5dxp.com
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
WH7PL
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Posts: 4




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« Reply #12 on: October 03, 2008, 12:19:32 PM »

I should have mentioned that the tuner is a auto antenna tuner and does not have a built in SWR meter.

The reason why I wanted the external SWR meter between the antenna and the tuner is so I could monitor the actual SWR as I moved the VFO across the band and if it became too high, I could go and adjust the antenna a bit so my transmitted signal would remain reasonably efficient.
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AA4PB
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« Reply #13 on: October 03, 2008, 01:18:14 PM »

Well, I'm another Extra that doesn't know that a tuner can reduce the SWR on the coax between the tuner and the antenna. I don't know that because it can't.

Yes, the tuner tunes the antenna system (meaning the antenna plus the coax) to resonance in that it cancels the reactance in the system but it does NOT change the SWR on the feed line between the tuner and the antenna. The only reason that the tuner might affect the forward power at its output is if the match at the transmitter is so high that the radio reduces its power output. Many transmitters have a fold back circuit to reduce output power in the presence of high SWR in order to protect themselves. At the point that happens you will see the forward and reflected power change anywhere in the system. The reflected power changes because the forward power changes, not because the SWR changes.

The traditional place for the SWR meter is between the radio and the tuner so that you can adjust the tuner for minimum SWR. I don't see a problem with placing it at the output of the tuner if you want to monitor the SWR on the line to the antenna. You can't use it to accurately adjust the tuner with it located at the output however.
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AA4PB
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« Reply #14 on: October 03, 2008, 01:35:42 PM »

I'm waging a crusade against the myth that the tuner accomplishes absolutely nothing between the tuner and the antenna.
------------------------------------------------------

1. It reduces the SWR on the coax between the transmitter and the tuner.

2. It provides a nice 50 ohm resistive load to the transmitter.

3. It does not reduce the SWR on the coax between the tuner and the antenna.

4. It does not reduce the loss in the coax between the tuner and the antenna.

The only real benefit is that the tuner provides a nice load to the transmitter. Other than that it doesn't improve the efficiency of the system or affect the amount of power radiated by the antenna.

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