cb swr meter for 10 meters

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joseph2020

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Is it safe to assume a SWR meter for CB (11 meter) will work on HF (10 meter) ? Thanks in advance.
 
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LtDoc

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I would think that it would be usable on 10 meters. But I would also take a few precautions, such as reducing power to something in the 5 - 10 watt range. Most SWR meters also have a watt meter, and the max range for that watt meter is typically the max power for the SWR meter.
None of this says how accurate, or what the meter's limits actually are, so...
- 'Doc
 

joseph2020

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LtDoc, Thanks for your reply. The radio is rated at less than 20 Watts PEP, the SWR meter at 1000 Watts. I am more concerned with the measurement accuracy more than anything else. I'm not sure, but I'm guessing with everything else being equal, the SWR reading between 10 and 11 meters would be close enough for practical work? Thanks again.
 
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kc4jgc

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Yes, because it's close enough in frequency, most if not all swr meters marketed for CB also works for 10m. My old meters even work down to 80m! Unless you find documentation otherwise, I would say yours would as well.
 

LtDoc

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Most SWR meters (CB/ham/commercial) have a wide enough usable frequency range that 10/11 meters really shouldn't be a problem. The readings from that meter ought to be 'accurate' enough, which just depends on who made the thing, some manufacturers aren't known for 'accuracy', much.
Use it. If it seems to be typically accurate, good enough.
- 'Doc
 

k9rzz

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You'll find no tuned circuits inside an SWR meter. As long as you don't over power it, no prob.

 
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joseph2020

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kc4jgc, LtDoc Thanks for your replies.

k9rzz, A special thanks for that schematic. I have looked at some in the past, but they all had either unobtainable components, or were imposible to understand. This one is realistically home "brewable". Maybe I'll try building one myself just for fun.

Any special construction hints that would be helpful? I have built plenty of circuits at home, both digital and analog but never any RF equipment. Any help would be appreciated. Thanks in advance.
 

LtDoc

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"You'll find no tuned circuits inside an SWR meter..."
Oh? What's the purpose of that RG-58A/U section in there? Any particular reason why RG-58A/U was chosen, and the significance of it's length? "Tuned" doesn't necessarily pertain just to frequency.
- 'Doc
 

joseph2020

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LtDoc
Oh? What's the purpose of that RG-58A/U section in there? Any particular reason why RG-58A/U was chosen, and the significance of it's length? "Tuned" doesn't necessarily pertain just to frequency.
Would you please answer the 2 questions you pose so that someone , not as knowledgeable as you (that would be me), can learn something form this? I am guessing the answer is "impedance", but not sure. Thanks in advance.
 
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Kennrth

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You did not mention the model of your Meter. The vast majority of cb swr/power meters will show little to no error reading swr since it is a relative measurement. Make sure you set your radio power output is set not to exceed max power capability of your meter. Use lowest power possible. Do not attempt to do this in single sideband. Use CW,FM,Am with no modulation.

Most modern radios have bar that shows relative output power. They have output Fet transistors which will fold back with excessive swr. Use the low power output setting of your radio will protect your output finals incase of bad mismatch. If there is a severe mismatch you will see the radio bar not come up or drop during transmit indicating very bad mismatch. Keep an eye on it. Of course it will be low bar indication relative to full power output when you set the radio to low power.
Put the meter in line in close to the radio in the swr position first. Key radio for quick reading. If SWR reading shows no reading (maybe a quick bleep on the meter) or exceeds 4 to 1 stop . (A severe mismatch will shut down your finals giving zero swr reading). Go no further you have a bad mismatch. Extended transmit may damage your radio. If reading is less than 4 to 1 go ahead.
Put Meter in Forward position for swr reading (cal Position) adjust cal for meter fullscale reading.
Then go back to swr position. Good match should be 1.5 or less. Most good matches should yield 1.3 or better in sweet spot in the band and 2 to 1 on the edges. Exceeding 2 will cause your radio's final to run a little warm . Stay under 2.5 to keep your finals overheating on extended transmit time. To get below 1.3 usually requires phase cutting your cable which is usually a waist of time.

Expect a power calibration error reading your power output but not likely to be more than 3 percent error that any reading on 11 meters. Most of these meters at best are +5 -5 percent anyway.
If you are a perfectionist there is a more accurate way to measure swr. Hams use this method when using cb swr meters bands like 2 meters or 6 meters. Insert the meter in the proper direction and set swr cal to full scale. Shut down your radio keep all settings the same. Careful not to touch the cal knob on the swr meter. Keep the swr meter in calibration position. Remove the meter and reinstall in reverse. Turn your radio back on and take your meter reading again while keying. This is your reflected power measurement which can be used to measure your swr. The lower the reading the better the match. There are many web sites that will show you how to calculate swr using forward and reflected power measurements.
Use a dead carrier with no modulation . Don't expect your cb meter to measure percent modulation if your radio is in FM .

As a side note; Your meters swr accuracy is dependent on adjusting your forward cal point to full scale
and going to the swr position and taking the measurement. The accuracy of the reading is directly related to the forward to reverse isolation capability at the frequency your using. A very good meter will have 40db of isolation between forward and reverse. 30db of isolation can cause 20 percent swr error reading error. So on 2 meters an 30db of isolation swr will could be 20 percent high. So a true swr of 1.5 would read 1.8 or 1.8. So still very usable. The difference between 10 and 11 meters would be negligible.
For those who intend to use a cb meter for 6 meters or 2 meters bands some meters have rf inductors inside which will not allow being used far out of band. But still very usable for 10 meters.

Hope this helps
 

N8IAA

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Ken, it appears that he hasn't been on RR since 9/2011. He even answered his own questions. But, who knows, he just might see your post:)
Larry
 

ke7htu

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I have about 8 swr meters and all work cb with most working up to 148 megs however its the power of the transceiver that is the key. You must not transmit more watts than the meter can handle or you will have to replace a diode or two. 1n914, etc. I have inadvertently done this a couple times but after spending several hours at the bench working on transceivers you tend to forget sometimes. :)
 
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