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Author Topic: SWR Meter Use - New Ham Question  (Read 5094 times)
KJAV
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Posts: 2




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« on: June 27, 2012, 06:26:37 PM »

Hello all. I am a new ham with recent Tech/General ticket, trying to get setup on HF.  I was hoping for some explanation as to how an SWR meter should behave.  I understand what it is measuring, but mine seems to be acting a bit strange.

I'm running an Icom 7000 with a DX-EE dipole antenna from Alpha Delta.  I currently have no tuner attached.  The test described below was at the 100W max limit of the radio, on 20 meters in the 14.250 to 14.340 range, SSB.

It was my understanding that the SWR meter should read anytime I am sending a carrier - basically any time I have the mic key'd.  When I key up, I always get SWR 1.0.  As I start to speak however, it spikes up - it bounces around with my voice.  I don't think SWR should change depending on strength of signal transmitted unless I misunderstand something.

If it does bounce around, then fine, but mine seems to want to be "all or nothing" - meaning, I can talk quietly and it will remain low or barely move, but it is very easy to peak it up into the red range (greater than 3.0 on my radio).

I recently made a contact on 20 meters (which this antenna should easily tune).  The contact told me I was strongly turning on and off.  We went back and forth, he suggested I adjust mic gain (it was set at 50% which is default on this radio).  Once I dropped the mic gain to 25%, he said I was 100% better sounding.

We chatted for a while and he surmised that the SWR was causing the output amp of the radio to shut off (probably on over drive protection) because the SWR was going so high.  Apparently lowering the amplitude of my mic driving the radio caused it to now remain below this point of clipping.

In lowering my transmitter power, I have noticed the following behavior....

- When setting to 5W, I can speak at a normal volume and I don't see the SWR go up at all - it remains at 1.0 the entire time.  It will however go immediately from 1.0 to max peaked level when I make hard sounds like "p" and "t".

- I see the same behavior as I increase power, but it becomes easier to make the meter peak out.


Does the actual SWR change with power?  Is it possible the antenna is interacting with nearby objects which are actually changing the tuning of the antenna as they reflect RF energy?

I do plan to add an antenna tuner soon, but I want to try and get my head around any root problems with the antenna itself before masking them behind a tuner.

That's a lot of information.  I'm hopeful others have seen and solved the problem.

Any help very much appreciated.

Thank you.
-Kevin

« Last Edit: June 27, 2012, 06:28:19 PM by KJAV » Logged
WB6BYU
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Posts: 13251




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« Reply #1 on: June 27, 2012, 07:25:19 PM »


It was my understanding that the SWR meter should read anytime I am sending a carrier - basically any time I have the mic key'd...



Actually, SSB doesn't work that way.  When properly adjusted there is no carrier
when you just squeeze the mic.  You have to be talking into it in order to get any RF
out of the transmitter.

I use CW to generate a carrier to check the SWR.  Others use AM, which does
generate a carrier when the mic is keyed with no modulation.   That gives you a
steady  output level to measure the SWR.

On SSB the output power - both forward and reflected - varies with the strength
of your modulation.  If your SWR meter shows both at the same time, you can
judge the ratio between them as an indicator of your SWR.  Otherwise, all you
are watching is reflected power, and that won't tell you the SWR since the
forward power is also jumping around.


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KI4SDY
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« Reply #2 on: June 28, 2012, 06:20:35 AM »

It would probably be a good thing to read the instructions that came with the meter. If you don't have the instructions, try to get them online. Many manufacturers post owner's manuals to minimize customer service calls. If you can't find the instructions online, go to the local ham store and see if they have the same or a similar meter for sale. Ask to look over the instructions and ask the sales person to explain how the meter controls work. If there is no ham store nearby, get an experienced ham to show you how the meter is supposed to work and write the instructions down. You can't tell what your antenna is doing if you don't know how to operate the SWR meter correctly.  Wink
« Last Edit: June 28, 2012, 06:22:53 AM by KI4SDY » Logged
W5DXP
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« Reply #3 on: June 28, 2012, 07:37:48 AM »

It was my understanding that the SWR meter should read anytime I am sending a carrier - basically any time I have the mic key'd.

You are not sending a carrier during SSB operation. It's one of the "suppressed carrier" modes. Use CW or AM to get an SWR meter reading.
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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.
KC9Q
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Posts: 49




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« Reply #4 on: June 28, 2012, 08:09:44 AM »

Why not use the built-in VSWR meter function on the IC7000?  Select RTTY mode to supply a carrier (i.e., just like the Turbo-Tuner does) and read the SWR directly.  While not as accurate as a dedicated VSWR Meter/Bridge, it will give you a very close reading as to what the radio is seeing.


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WB6BYU
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Posts: 13251




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« Reply #5 on: June 28, 2012, 10:08:24 AM »

So to clarify the process:  an SWR meter basically reads FORWARD and REFLECTED power.
When the sensitivity control is adjusted so that FORWARD power is at full scale, then when
you switch the meter to REFLECTED the scale is calibrated in SWR (being a function of the
ratio between FORWARD and REFLECTED power.)

With SSB there shouldn't be any output power when you just key the mic, only when you
are speaking into it, and then the power varies with the speech waveform.  This makes it
very difficult to maintain a consistent output to set the FORWARD reading to full scale.
It also means that, if you are only looking at the SWR setting (that is, the REFLECTED power
level), it will jump all over the meter as you talk, because it is some portion of the
FORWARD power, which is also jumping all around.

So the SWR scale ONLY reads SWR accurately when the sensitivity control has been set
so the meter reads full scale in the FORWARD mode.  (This is assuming you have an external
SWR meter - you don't say what you are using for the measurement.)  Most SWR meters
will read 1 : 1 when there is little or no drive power, as is the case when you key the mic
in SSB mode, or when the output power is below the calibrated drive level for the meter.


The simple solution is to use CW, RTTY or AM modes to generate a steady signal for
taking the measurement.
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M6GOM
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Posts: 907




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« Reply #6 on: June 28, 2012, 12:17:37 PM »

Why not use the built-in VSWR meter function on the IC7000?  Select RTTY mode to supply a carrier (i.e., just like the Turbo-Tuner does) and read the SWR directly.  While not as accurate as a dedicated VSWR Meter/Bridge, it will give you a very close reading as to what the radio is seeing.




Far better is to press and hold the MENU/GRP button down until you get to this screen here.
http://www.benlo.com/ham/ic-7000/ic-7000-front.jpg

Then press it briefly until you get the SWR plot meter. Press F1 and then key the mike and as you key it it'll move to the next segment and repeat until it gets all the way to the right and give you a SWR sweep of your antenna on that band. Press the F4 key to change the step.
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W9KDX
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Posts: 770




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« Reply #7 on: June 28, 2012, 01:53:15 PM »

It would probably be a good thing to read the instructions that came with the meter. If you don't have the instructions, try to get them online. Many manufacturers post owner's manuals to minimize customer service calls. If you can't find the instructions online, go to the local ham store and see if they have the same or a similar meter for sale. Ask to look over the instructions and ask the sales person to explain how the meter controls work. If there is no ham store nearby, get an experienced ham to show you how the meter is supposed to work and write the instructions down. You can't tell what your antenna is doing if you don't know how to operate the SWR meter correctly.  Wink

That might be a good suggestion if things came with any instructions these days.  The last meter I got neglected to mention how to measure SWR by looking at the point where the needles intersect.  They must have just assumed we all know that.

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Sam
W9KDX
KI4SDY
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Posts: 1452




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« Reply #8 on: June 28, 2012, 05:45:00 PM »

Man, that must have been a cheap CB meter! I have never bought a good one that did not come with instructions. Maybe somebody returned it and forgot to put the instructions back in the box before you bought it.  Wink
« Last Edit: June 28, 2012, 06:00:59 PM by KI4SDY » Logged
WB6BYU
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Posts: 13251




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« Reply #9 on: June 28, 2012, 09:45:48 PM »

Quote from: KI4SDY
Man, that must have been a cheap CB meter! I have never bought a good one that did not come with instructions.


The instructions for an SWR meter designed for CB use very likely would assume that the
radio was operating AM, so there would be a carrier when the mic button was squeezed.

If the SWR meter is the one built into the radio, then the instructions would be different.
But we don't know which one it is yet.


There is a lot of complexity and "lore" to learn in ham radio.  While this forum is pretty good
for giving advice, there are lots of things that are easier to learn from someone sitting with
you who can see everything you are doing:  often the problem is not where you would
think to look for it.
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KI6LCY
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Posts: 5




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« Reply #10 on: June 28, 2012, 10:12:42 PM »

How would one generate a CW with say a HT or mobile dual band?

I'm using a Radio Shack SWR meter, and I need to get to a CW  or tuning mode to test SWR, but I can't figure out how to do that with a FT8800.

Rob
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K2OWK
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Posts: 1061




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« Reply #11 on: June 29, 2012, 12:02:38 AM »

The FT-8800 is an FM transceiver. Its carrier is on when you key the mike. No CW mode is required. Just key the mike and read power out (50watts or 35 watts) and check the VSWR with your meter. Make sure that the SWR meter you use is capable of reading the frequencies of the 8800 (2 meters and .70 centermeters).

73s

K2OWK
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KI4SDY
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Posts: 1452




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« Reply #12 on: June 29, 2012, 06:07:44 AM »

There is a lot of complexity and "lore" to learn in ham radio.  While this forum is pretty good
for giving advice, there are lots of things that are easier to learn from someone sitting with
you who can see everything you are doing:  often the problem is not where you would
think to look for it.

I already suggested that.  Wink
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W5DXP
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Posts: 3583


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« Reply #13 on: June 29, 2012, 09:23:20 AM »

... often the problem is not where you would think to look for it.

Often the person asking the question doesn't know what question to ask. He wants to know what time it is and we tell him how a clock's spring action is synchronized to the rotation of the earth. Smiley
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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.
KI6LCY
Member

Posts: 5




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« Reply #14 on: June 29, 2012, 09:24:06 AM »

That Radio Shack meter apparently doesn't work with the 8800.

I saw a suggestion that I reverse the connections; I tried that method and it seemed to work. Not sure about the accuracy though....

Rob
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