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Author Topic: Do you NOT always keep your SWR meter inline due to insertion loss?  (Read 9842 times)
G3RZP
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« Reply #15 on: August 20, 2012, 08:19:54 AM »

In the days of VHF (low band) TV, when harmonics were a definite problem, it was best to have the low pass filter between the antenna and the SWR bridge. This was because the diodes in the bridge could produce enough harmonic energy to cause quite severe TVI. But because of the filter mismatch (there's always some!) the SWR never got as low as people felt it should. Since those were the days of tuned tube PAs, it didn't matter. But anywhere that's left with low band VHF TV, it might better to not leave the SWR meter in circuit.
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G3TXQ
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« Reply #16 on: August 20, 2012, 08:30:31 AM »

But anywhere that's left with low band VHF TV, it might better to not leave the SWR meter in circuit.
Or, perhaps, use an SWR meter that doesn't have diodes!

Steve G3TXQ
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N4CR
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« Reply #17 on: August 20, 2012, 04:23:50 PM »

I measure the insertion loss of my LP100 sense head as 0.022dB at 30MHz; I think I'll leave it in  Wink

Steve G3TXQ

How did you measure that? I've always wondered what the insertion loss was on my LP-100a.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
G3TXQ
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« Reply #18 on: August 21, 2012, 12:26:52 AM »

An S21 measurement on a 2-port VNA. It wont be accurate to 0.001dB, but it will be in the right "ball park"!

73,
Steve G3TXQ
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F8WBD
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Posts: 63




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« Reply #19 on: August 22, 2012, 05:34:33 AM »

My OHR QRP wattmeter is always in line with my FT-817. Use a short RG8x connection between the two. No tuner employed. Not necessary with my Par end fed wire.
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AA4HA
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« Reply #20 on: August 22, 2012, 01:18:04 PM »

Get yourself a good Peak Envelope Power Meter/SWR and leave it inline.
A good PEP/SWR Meter is the N8LP LP100A meter. It is pricey, but well worth the investment in the long run, and it is very accurate.

http://www.telepostinc.com/lp100.html

http://www.eham.net/reviews/detail/5981

Just my $0.02 worth.

(((73))) Milverton.

There seem to be quite a few Bird Model 43's floating around. They have very minimal insertion loss. I leave them in-line and usually have the slug rotated to look at reverse power. If I transmit and that needle jumps I know immediately that I have a major problem and shut down to go looking for a fried balun, coax issue, etc...

For about $40 you can buy a Peak Envelope Power (PEP) board that goes inside of a Bird wattmeter. It is a tremendously complicated kit to install. it attaches to the two panel meter lugs inside of the Bird 43, has a 9 volt battery, LED a power switch and another switch to go from PEP to normal operation. It took like an entire 10 minutes to install.

What is nice about Bird is that you can get slugs for anything from the AM broadcast band well up into the microwave spectrum. Also slugs are available at a variety of power ratings from 0-1 watt for a portable radio up to 0-10 kilowatts for commercial transmitters.

The slugs can also be the not so nice part as well. Prices on eBay can vary from $20 US up to $300 depending upon the supplier. You are not limited to just Bird slugs, there are several companies that make slugs that work in a bird wattmeter.

or, buy a Telewave with a rotary switch for power levels. Most folks are not calibrating a transmitter where you need to know within 2% of what the forward or reflected power is.

Oh, a major downside. You might want to download a little graph that shows you what the SWR is depending upon the forward vs. reflected power readings. You get both numbers just by rotating the slug 180 degrees in the socket. No crossed needles on this type of wattmeter or a little switch to go from FWD to REF.
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
K2UE
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« Reply #21 on: August 26, 2012, 05:16:46 AM »

Insertion loss = Heat.  If it's not warm when you transmit, there's no point in removing it.
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W8JI
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« Reply #22 on: August 26, 2012, 03:11:02 PM »

An S21 measurement on a 2-port VNA. It wont be accurate to 0.001dB, but it will be in the right "ball park"!

73,
Steve G3TXQ

I thermally measured loss in a directional coupler I did some time ago.

It was ~.008 dB on almost all bands, just very slightly higher on ten meters than 160 or 80 meters. Nearly all loss was in the current transformer termination. It was a little difficult to not have the cables mess up the readings, but I think I got it pretty close. If the cables were sucking out more heat than I expected, then it would be less than .008 dB

I think .022 dB is high. That would be about 8 watts of heat at 1500 watts. I can't think of any meters that get that warm.



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W0BTU
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« Reply #23 on: August 26, 2012, 05:00:36 PM »

Insertion loss = Heat.  If it's not warm when you transmit, there's no point in removing it.

VERY well said, indeed! That is exactly right. This answer gets right to the heart of things.

People are always asking questions like this, wondering if they can make their signal stronger (or hear better) by doing something like this that won't make one bit of difference.

Some similar non-issues we hear discussed all the time are small losses in tuners, antenna switches, coax, or if connectors such as N connectors are better than PL-259s, or if our signal will be louder if we switch to some expensive coax on HF that they've seen advertised. (Or maybe stranded vs. solid wire, or insulated vs. uninsulated wire for our antennas.) And the list goes on.

In order for anything to lower the loss significantly, whatever we take out of the line has to be producing lots of heat that we can burn our fingers on, smell, or see the smoke. :-)

Leave your SWR meter in line and don't worry about it.
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K7KBN
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« Reply #24 on: August 26, 2012, 08:09:36 PM »

My advice is always the same:  try it and see how much difference it makes.
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73
Pat K7KBN
CWO4 USNR Ret.
KG6MZS
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Posts: 476




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« Reply #25 on: August 27, 2012, 07:25:39 AM »

Some similar non-issues we hear discussed all the time are small losses in tuners, antenna switches, coax, or if connectors such as N connectors are better than PL-259s, or if our signal will be louder if we switch to some expensive coax on HF that they've seen advertised. (Or maybe stranded vs. solid wire, or insulated vs. uninsulated wire for our antennas.) And the list goes on.

I understand what you are saying, but sometimes I think of the expression we have in backpacking: "Ounces make pounds."  The idea being that if you add up enough insignificant losses, they become significant.

That being said, my Palstar AT2K is always inline, so I always have the rig's meters and the cross needles on the tuner, even in bypass.
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SWMAN
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« Reply #26 on: August 27, 2012, 11:31:16 AM »

I dont ever keep mine inline, I just use the one on the radio which works fine. I use all single band tuned antennas so I dont really need it all of the time. 73 Jim W5JJG
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W9MMS
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Posts: 119




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« Reply #27 on: August 27, 2012, 11:56:38 AM »

Insertion loss = Heat.  If it's not warm when you transmit, there's no point in removing it.

VERY well said, indeed! That is exactly right. This answer gets right to the heart of things.

People are always asking questions like this, wondering if they can make their signal stronger (or hear better) by doing something like this that won't make one bit of difference.

Some similar non-issues we hear discussed all the time are small losses in tuners, antenna switches, coax, or if connectors such as N connectors are better than PL-259s, or if our signal will be louder if we switch to some expensive coax on HF that they've seen advertised. (Or maybe stranded vs. solid wire, or insulated vs. uninsulated wire for our antennas.) And the list goes on.



In order for anything to lower the loss significantly, whatever we take out of the line has to be producing lots of heat that we can burn our fingers on, smell, or see the smoke. :-)

Leave your SWR meter in line and don't worry about it.

Is this the "ELMERING" Forum?

>>>> People are always asking questions like this, wondering if they can make their signal stronger (or hear better) by doing something like this that won't make one bit of difference. <<<<
I guess there is really Dumb questions then! Huh
I guess THOMAS EDISON's was also a question of "NON ISSUE" and did not make " one bit of difference " when he stumbled upon the Phonograph in Menlo Park?
>>> " The first great invention developed by Edison in Menlo Park was the tin foil phonograph. While working to improve the efficiency of a telegraph transmitter " <<<< end of quote.

The question was asked in earnest, which in my opinion (for what it's worth) makes it a legitimate question.
Sometimes, we (collectively) need to be a little bit more tolerant of others.

(((73))) Milverton.  
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W0BTU
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« Reply #28 on: August 27, 2012, 12:51:26 PM »

If my reply sounded intolerant, I didn't mean to. I was just trying to get a point across that many other people have also asked about on the forums.

Basically, if it doesn't get quite warm to the touch when we transmit (at say, 100 watts on CW or RTTY) for awhile, then the loss is nothing to be concerned about.

Even when we add up all the normal I2R losses in our connectors, switches, SWR and power meters together, the tiny fraction of a dB that it all adds up to is seldom going to make any difference in how well our signal gets heard at the other end.

Here is some food for thought: http://www.vk1od.net/transmissionline/concept/iltl.htm
« Last Edit: August 27, 2012, 01:03:55 PM by W0BTU » Logged

W8JI
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« Reply #29 on: August 27, 2012, 04:51:18 PM »

If my reply sounded intolerant, I didn't mean to. I was just trying to get a point across that many other people have also asked about on the forums.

Basically, if it doesn't get quite warm to the touch when we transmit (at say, 100 watts on CW or RTTY) for awhile, then the loss is nothing to be concerned about.

Not always.

If we lose 20-30 watts out of 1500 in an antenna tuner inductor, it can melt the inductor down.

If we lose 300 watts out of 1500 in a 100-foot long feeder, we may not notice.

How well something gets rid of heat matters just as much as how much heat we have to get rid of. :-)


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