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   Home   Help Search  
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Author Topic: SWR HELP  (Read 3915 times)
KM6NFF
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Posts: 139




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« on: April 09, 2018, 01:28:24 PM »

Hello all. I've been in Ham Radio for about 5 months now and have a SWR question. I have a Icom 7300 with a Comet 250B vertical antenna. The SWR on the radio looks good but do you suggest an additional SWR meter inline? Right now I have a low pass filter in place and was wondering about an SWR meter. Thanks
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AA4PB
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« Reply #1 on: April 09, 2018, 02:32:32 PM »

The SWR meter built into the 7300 should be fine. Remember that with the tuner on, you will be reading the SWR on the transmitter side of the tuner (which should always be low). Turn the tuner off to see the real SWR on the antenna feedline.

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Bob  AA4PB
Garrisonville, VA
KB2WIG
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Posts: 541




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« Reply #2 on: April 09, 2018, 02:34:14 PM »


If the SWR looks "good" why are you asking? Is there something else going on, or you just don't trust your Icom
? Not trying to dump on you, just asking for clarification. I'll guess you've made contacts with this setup.

5 months experience- your getting into HF on the ground floor of the cycle. Pretty much nowhere to go but up, propigation wise.

KLC
« Last Edit: April 09, 2018, 02:43:01 PM by KB2WIG » Logged

EXTRALight  1/3 less WPM than a Real EXTRA
KM6NFF
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Posts: 139




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« Reply #3 on: April 09, 2018, 02:38:33 PM »

I am making contacts and the previous comment is right as well I guess. The radio is reading a very low SWR so I guess I'm good to go. Thanks
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AC2EU
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« Reply #4 on: April 09, 2018, 02:43:10 PM »

If the radio can tune the antenna with the internal tuner, there is no real need for an external "anything".
It's just when you have a non resosnant antenna that you may need to tune into greater than 3:1 SWR that you might consider an outboard tuner/SWR meter.
You are better off being less than 3:1 SWR , anyway, you will have better efficiency. That is why the radio MFRs don't go beyond that.
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WA3SKN
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« Reply #5 on: April 09, 2018, 02:49:17 PM »

Why the low pass filter?  Problems?

-Mike.
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KM6NFF
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« Reply #6 on: April 09, 2018, 02:51:31 PM »

Honestly I put on the filter to avoid any issues. Do you think that is wrong? It was just an idea but what do you think?
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KB1GMX
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Posts: 1658




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« Reply #7 on: April 09, 2018, 03:01:56 PM »

Unless the internal circuit is broken an external one is not needed.

If you have an internal tuner and using it then external meter not indicate what the
transmitter sees as you cannot interrupt the path between the transmitter and the internal tuner.

If you have an internal tuner and using it then external low pass filter you cannot use it
as you cannot put it in between the transmitter and the internal tuner.

If used external to the radio it may not perform well as then its not terminated
with 50 ohms with any certainty on either end again due to the tuner.

The only way to use a filter and external meter is turn off the internal tuner and
use an external one.  In that case the order is radio to the filter, then SWR meter,
and then tuner.  There might be reasons for doing that but modern radios have
good metering, filtering, and the tuner is handy.


Allison
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KM6NFF
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« Reply #8 on: April 09, 2018, 03:09:38 PM »

That's good to know,thanks
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AA4PB
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« Reply #9 on: April 09, 2018, 03:17:54 PM »

Low pass filters are pretty much a relic of the old tube days when transmitters often didn't have sufficient internal filtering.
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Bob  AA4PB
Garrisonville, VA
KM6NFF
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« Reply #10 on: April 09, 2018, 03:20:51 PM »

I didn't know that. Its good to know.
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W5DXP
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« Reply #11 on: April 09, 2018, 03:24:54 PM »

If you want an external SWR meter, you might get an antenna analyzer that not only indicates the SWR but also the impedance including the sign of the reactance.
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73, Cecil, w5dxp.com
KM6NFF
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Posts: 139




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« Reply #12 on: April 09, 2018, 03:40:22 PM »

I think I'll stick with what I have and forget about an external swr.
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W8JX
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« Reply #13 on: April 09, 2018, 06:49:11 PM »

Low pass filters are pretty much a relic of the old tube days when transmitters often didn't have sufficient internal filtering.

Actually it is more of a relic of old broadcast analog TV starting at 54 mhz in past. TV channels  2 thru 6 could have harmonic radiation interference. I really do not think modern SS rigs with broad band tuned output are better than old tube finals that had manually tank circuits  for harmonics.
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--------------------------------------
Ham since 1969....  Old School 20wpm REAL Extra Class..
K0UA
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« Reply #14 on: April 09, 2018, 08:16:13 PM »

A couple more things to keep in mind from a fellow IC7300 owner.  The CHA250B antenna  presents a good match to the rig even without a tuner.  Usually under 2:1 SWR across the whole HF spectrum due to its broadband transformer and design.  BUT you pay for that with a very low efficiency antenna.  Of course I don't know your property restrictions or what you can do antenna wise, but almost any wire antenna will outperform the CHA250 by many many dB.  Everything "works", dummy loads with T connection and a bit of wire strung out , light bulbs , little whips on the patio etc. It all works to varying degrees.  But if you had even dipoles for each band, your 7300 would think it died and went to heaven from the amount of signals you would now hear AND work!.

The SWR meter is a very good one in the 7300, and it even has the SWR plotting function (consult your manual) that you can use to plot your SWR (without the tuner engaged) for each band. Kind of a gimmick, but also kinda cool too.

Keep in mind that SWR, while a useful thing to measure, has nothing at all to do with antenna efficiency.  If you have a good SWR match your rig will put out full power, but that doesn't mean the antenna will actually radiate much of it.  As an example  a good shielded dummy load is a very poor radiator, but it is an excellent match to your rig.  NO tuner required.  I am reading between the lines here, but I suspected that the reason you asked about the external SWR meter is because you are not entirely happy about the way your antenna performs?   I could be wrong.
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