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SWR Meter Placement For Tuning With Amplifier

Capt Crunch

Captain Crunch NJ Mobile
Nov 3, 2015
160
210
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New Jersey
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SWR antenna tuning. From what I read for amps the SWR should be less than 1.5 going in. I see many talk about where the SWR Meter goes and most say by the radio or after the amp or both. If I am wanting to get low SWR into the amp wouldn't I want the meter just before the amp? I usually tune antenna swr with the radios meter with amp inline and off. I have also used 2 meters one at radio and one after the off amp and adjusted each as close as I could. I have never did the right before the amp one but I am questioning if that would be the best place because I want the lowest SWR going into the amp, and obviously watching it at the radio as well. Thanks in advance.
 
Last edited:

loosecannon

Sr. Member
Mar 9, 2006
4,195
3,588
273
the amp needs to be on in order to see the input tune.

with the amp off, you are seeing the SWR of the antenna, as the amp relay contacts are just passing the signal right through the amp.

first, just because of the way you worded things, i want to make sure you're not saying that you are using the SWR meter itself as some sort of "tuner".

to see how well you're amp's input tuning is matched to your radio, you can use the radio's internal SWR meter, or if the radio doesn't have one, you can put an SWR meter in between the radio and the amp temporarily.

now with the amp on, and an antenna or dummy load connected to the output of the amp, key the mic, calibrate the SWR meter, switch it to read SWR, and note the value shown. It should be less than 2:1 and preferably 1.5:1 or better.

now to see how well the output of your amp is matched to your antenna, put the SWR meter between the amp and the antenna, and repeat the test. amp on of course.
LC
 

wavrider

W9WDX Amateur Radio Club Member
Jun 2, 2009
3,404
1,268
173
If the amp is a tube type amp then the amplifier also needs to be tuned.

Radio>>>> VSWR meter>>>> amplifier>>>> watt meter>>> dummy load or antenna

Turn amp on and tune it as it should be tuned, dip plate tune the load !!!!
now that the amp is tuned
with no modulation,,cw , fm mode,\ or am carrier,,key radio and amp, calibrate vswr meter between radio and amp,,,check INPUT VSWR, or input impedance to the amplifier. Adjust input tune as needed with the variable inductors or caps or whatever flavor your amp has for adjustable input tune. adjust to lowest you can get.
now if your going work warc bands you will have to fine tune the 10 meter/15 meter input for 12 and 17 meters, make sure your plate choke will allow you to use warc freq.
DO THIS FOR ALL BANDS THE AMP HAS.

As for the VSWR of output????? that is your antenna system and a whole nother topic.
 
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Capt Crunch

Captain Crunch NJ Mobile
Nov 3, 2015
160
210
73
New Jersey
www.iamawesome.com
the amp needs to be on in order to see the input tune.

with the amp off, you are seeing the SWR of the antenna, as the amp relay contacts are just passing the signal right through the amp.

first, just because of the way you worded things, i want to make sure you're not saying that you are using the SWR meter itself as some sort of "tuner".

to see how well you're amp's input tuning is matched to your radio, you can use the radio's internal SWR meter, or if the radio doesn't have one, you can put an SWR meter in between the radio and the amp temporarily.

now with the amp on, and an antenna or dummy load connected to the output of the amp, key the mic, calibrate the SWR meter, switch it to read SWR, and note the value shown. It should be less than 2:1 and preferably 1.5:1 or better.

now to see how well the output of your amp is matched to your antenna, put the SWR meter between the amp and the antenna, and repeat the test. amp on of course.
LC
Ok thanks. I meant tune antenna swr. I have a meter in the radio. In the beginning and over the years when asking I was told to check swr at the radio and tune it from there with amp on. Then someone told me to do it with amp off. Then I was told to tune swr with amp off as it bypasses the amp and then if you turn it on and its way off it could be the amp tune. I have also been told to use two meters one in radio and 1 after amp on antenna side with amp off and tuned like that and tried to get both as low as possible. So thats my confusion going on.
 
Last edited:

Capt Crunch

Captain Crunch NJ Mobile
Nov 3, 2015
160
210
73
New Jersey
www.iamawesome.com
If the amp is a tube type amp then the amplifier also needs to be tuned.

Radio>>>> VSWR meter>>>> amplifier>>>> watt meter>>> dummy load or antenna

Turn amp on and tune it as it should be tuned, dip plate tune the load !!!!
now that the amp is tuned
with no modulation,,cw , fm mode,\ or am carrier,,key radio and amp, calibrate vswr meter between radio and amp,,,check INPUT VSWR, or input impedance to the amplifier. Adjust input tune as needed with the variable inductors or caps or whatever flavor your amp has for adjustable input tune. adjust to lowest you can get.
now if your going work warc bands you will have to fine tune the 10 meter/15 meter input for 12 and 17 meters, make sure your plate choke will allow you to use warc freq.
DO THIS FOR ALL BANDS THE AMP HAS.

As for the VSWR of output????? that is your antenna system and a whole nother topic.
Ita a Carl Built 400HDHG. I meant tune antenna swr not amp or radio.
 
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kopcicle

Sr. Member
Feb 17, 2016
2,073
3,303
273
Wow ,
I really will try to make this as simple as possible.
I'm including a TLDR version below.

First we have to establish a few definitions.

Voltage Standing Wave Ratio , otherwise VSWR, vswr, or swr (yuck) This last is a bit lazy and not quite correct so I ...

Additional notes and links:

Standing up for standing waves. Probably the best 90min you'll ever spend understanding radio waves in general.


Vizwarz, or how to get it wrong on so many levels.
https://forums.qrz.com/index.php?threads/vizwarz-or-only-your-barista-knows-for-sure.594793/

Another look at reflections. This is admittedly advanced material and will either make your head hurt and eyes bleed, or put you to sleep. In any case it had to be mentioned.
http://www.k3emd.com/downloads/Reflect.pdf

Resonance.
Resonance is not impedance. Let's try that again, with feeling , Resonance is Not VSWR. Resonance can be at minimal vswr, or not. Minimum vswr can be at resonance, or not. The two are interrelated but mutually exclusive and separate terms.

We currently have cool toys like rig expert and nano vna. but unless you anticipate frequently tossing wire around the property even the $99 VNA is overkill.

So with those definitions and links in place:
Place a dummy load on the output of the amplifier and without plugging it in or turning it on check the vswr between the radio and the amp. This first easy step will prevent issues later. Any bypass vswr has to be eliminated. Methods are a swamping resistor(s), constant impedance attenuator (3Db "T" pad) , or a lump constant tuned circuit ( capacitor/inductor network) Once the vswr barely if at all registers , move on .

Next, turn the amp on and with reasonable input observe the input vswr with the amp output into a dummy load. Again if this circuit displays significant vswr a swamping resistor(s), constant impedance attenuator (3Db "T" pad) , or a lump constant tuned circuit ( capacitor/inductor network) are needed to adjust the input vswr across the intended range of operation. I don't mean to gloss over all that this entails because you simply asked "where does the vswr meter go" . What you didn't know is that this opens a YUUUUUge can of worms.

So now you have a radio that drives an amplifier without seeing significant vswr. You have some significant output at the exit of the amplifier. What next?

A brief look at drive and efficiency.
One watt in = 10 watts out
Two watts in = 20 watts out
Three watts in = 30 watts out
Four watts in = 40 watts out
....

This is "linear" behavior.

14.49A @ 13.8V for 100 watts output.
This amplifier is 50% efficient. Take my word for it or do the math :)

Fully modulated AM output is four times the quiescent carrier. So four watts carrier fully modulated is 16 watts.
Now do you understand why a pair of 2sc455's or even 2sc2290's only need 2-3 watts of drive?

So the easiest way to establish drive level is watts input/output vs current draw. Simply put if the next amp you draw is only producing 25% more output than the last amp you drew it's time to back off. How much you back off depends on how deep your pockets are.

Okay now we're at the voodoo where resonance does not equal resistance. Resonance is NOT necessarily at 1:1 vswr.
A dummy load has a perfect 1:1 match but isn't much of antenna by design. Off Center Fed Dipoles are regularly fed at a 200 ohm point and are great antennas. Several constructions of wire antennas are resonant at frequency and exhibit feed point impedance in the several thousands of ohms.

From the above link to the antenna handbook find the chapter on matching sections. If the dimensions of the antenna make any realistic sense IE: 9 foot whip, 18 foot dipole, or any reasonable fraction or multiple there of you can continue.
You have two choices here, fool the amp into seeing a flat match with a tuner or fix the antenna feed point. The alternative is to place the tuner at the antenna feed point but not always convenient.
The best of the two choices as to fix the feed point so that your coax or other feed line isn't confused and either radiating or heating.
Mismatches under 2.5:1 (opinion) result in such minimal losses that placing the tuner at the amp output is acceptable if not ideal.

so the TLDR version as promised. An even shorter version follows this one.
Both goesinta and goesouta vswr/power meters.

Resonance does not equal vswr

For solid state devices an amp meter really really really helps set appropriate drive levels.

Do not over drive the poor beastie. You will let the smoke out.
If you're getting 100 ish (peak reading)output for around 15A @ 13.8V, out for 3 watts in on AM with a tone or whistle with a 25-30 dead carrier out of a random pair of magic smoke containment devices be happy.

12-14V DC MOSFET amplifiers are an absolute minefield.
I avoid them like my future ex-wife.

Amp bypass and amp input vswr are two separate circuits.

If the amp and the antenna are at or near 50 ohms the feed line becomes practically invisible save for it's losses.

It's not rocket surgery but it is brain science.

TLDR:
Both
Don't overdrive it or gawd will kill a kitten.
 

Dr_DX

Well-Known Member
Jan 29, 2006
236
280
73
Just my .02...

For any SWR meter that rectifies RF through a diode (SWR meter in a radio, most external SWR meters) to be accurate, it needs to be directly connected to the load/antenna or use a 1/2 wave length jumper connected to the load/antenna to be accurate.

Why: Because the RF going through the coax will be at the same potential on each end of a 1/2 wavelength of coax (or multiple of). Therefore, when the RF is rectified, it will give the same reading on the SWR meter. This is the reason you will see different SWR readings when you change your jumper to a longer or shorter one or a different efficiency when there is reactance in the load.

IMHO, to properly "tune" your antenna, you can use a meter or analyzer to get a "ballpark" tune by connecting directly to the antenna or through a 1/2 wavelength coax.

The "final" tune should always be with the amp on and at full output with everything in place and how you plan on running things.

Since your Carl Built doesn't have a SWR meter in it, use a double male pl-259 and attach a SWR meter directly to the output connector. Connect a 1/2 wavelength coax or multiple of (what ever it takes to reach the antenna). Make sure the SWR meter can handle the output of the Carl Built. Tune antenna for lowest reflect on the meter.

I prefer this kind of SWR meter as it uses a straight through design (uses inductive coupling) and has minimal impact when placed in line. They were all made in the same Japanese factory - just had different names put on them. They are good for 1KW. Also recommend disconnecting the 2 diodes on the FS connection so stray RF doesn't come in on it.

https://www.ebay.com/itm/165262121844?hash=item267a63db74:g:LBIAAOSwmSlh0Gcq

https://www.ebay.com/itm/255318322901?epid=778359977&hash=item3b72286ed5:g:Ys0AAOSw-2thXxu4

https://www.ebay.com/itm/144323966329?epid=2254344538&hash=item219a60f579:g:sREAAOSweJ9hsVo6

If you are going to run a SWR meter permanently, try finding one that has a remote sense that can handle 1KW and connect the remote directly to the output of the Carl Built.

For adjusting the input SWR on the Carl Built, that is done internally in the box. The pic is the input/output relay in the 400HD. It is not an RF relay, it is a power relay. It is not deigned to maintain a 50 ohm impedance between its contacts.

The lower green wire is the input. I see a single Silver Mica to ground (to the right of the input wire). If it is built right, that will be from the N/O relay contact to ground. You can adjust that value to change your input SWR when the box is ON. You will see a very short wire that goes between the 2 N/C relay contacts on the top of the relay. You can add capacitance (picofarads) to circuit ground there to adjust your input SWR when the box is OFF.

input and output relay.jpg
Good Luck!
 
Last edited:
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Capt Crunch

Captain Crunch NJ Mobile
Nov 3, 2015
160
210
73
New Jersey
www.iamawesome.com
Just my .02...

For any SWR meter that rectifies RF through a diode (SWR meter in a radio, most external SWR meters) to be accurate, it needs to be directly connected to the load/antenna or use a 1/2 wave length jumper connected to the load/antenna to be accurate.

Why: Because the RF going through the coax will be at the same potential on each end of a 1/2 wavelength of coax (or multiple of). Therefore, when the RF is rectified, it will give the same reading on the SWR meter. This is the reason you will see different SWR readings when you change your jumper to a longer or shorter one or a different efficiency when there is reactance in the load.

IMHO, to properly "tune" your antenna, you can use a meter or analyzer to get a "ballpark" tune by connecting directly to the antenna or through a 1/2 wavelength coax.

The "final" tune should always be with the amp on and at full output with everything in place and how you plan on running things.

Since your Carl Built doesn't have a SWR meter in it, use a double male pl-259 and attach a SWR meter directly to the output connector. Connect a 1/2 wavelength coax or multiple of (what ever it takes to reach the antenna). Make sure the SWR meter can handle the output of the Carl Built. Tune antenna for lowest reflect on the meter.

I prefer this kind of SWR meter as it uses a straight through design (uses inductive coupling) and has minimal impact when placed in line. They were all made in the same Japanese factory - just had different names put on them. They are good for 1KW. Also recommend disconnecting the 2 diodes on the FS connection so stray RF doesn't come in on it.

https://www.ebay.com/itm/165262121844?hash=item267a63db74:g:LBIAAOSwmSlh0Gcq

https://www.ebay.com/itm/255318322901?epid=778359977&hash=item3b72286ed5:g:Ys0AAOSw-2thXxu4

https://www.ebay.com/itm/144323966329?epid=2254344538&hash=item219a60f579:g:sREAAOSweJ9hsVo6

If you are going to run a SWR meter permanently, try finding one that has a remote sense that can handle 1KW and connect the remote directly to the output of the Carl Built.

For adjusting the input SWR on the Carl Built, that is done internally in the box. The pic is the input/output relay in the 400HD. It is not an RF relay, it is a power relay. It is not deigned to maintain a 50 ohm impedance between its contacts.

The lower green wire is the input. I see a single Silver Mica to ground (to the right of the input wire). If it is built right, that will be from the N/O relay contact to ground. You can adjust that value to change your input SWR when the box is ON. You will see a very short wire that goes between the 2 N/C relay contacts on the top of the relay. You can add capacitance (picofarads) to circuit ground there to adjust your input SWR when the box is OFF.

View attachment 49521
Good Luck!


I gather you mean at the ANT connector at the back of the amp. I have done this. I had to use both the radios swr meter and the one after the amp with a male to male connector and a Nessi RS-27 meter. I was told when doing it this way to balance at the radio and after the amp, as I do a 1 and 40 match tune. The SWR at the radio is reading backwards of the after the amp meter. With the amp on I can get it at 1.3 on the radio and 1.5 after the amp. I use two jumpers 15ft LMR400UF. One radio to amp and one amplifier to antenna. I thank you for all the info although I am clumsy and not technical at all and would probably f up anything I try that is explained to me inside the amp LOL. Hence the reason I was asking here.
 
Last edited:

Capt Crunch

Captain Crunch NJ Mobile
Nov 3, 2015
160
210
73
New Jersey
www.iamawesome.com
Wow ,
I really will try to make this as simple as possible.
I'm including a TLDR version below.

First we have to establish a few definitions.

Voltage Standing Wave Ratio , otherwise VSWR, vswr, or swr (yuck) This last is a bit lazy and not quite correct so I ...

Additional notes and links:

Standing up for standing waves. Probably the best 90min you'll ever spend understanding radio waves in general.


Vizwarz, or how to get it wrong on so many levels.
https://forums.qrz.com/index.php?threads/vizwarz-or-only-your-barista-knows-for-sure.594793/

Another look at reflections. This is admittedly advanced material and will either make your head hurt and eyes bleed, or put you to sleep. In any case it had to be mentioned.
http://www.k3emd.com/downloads/Reflect.pdf

Resonance.
Resonance is not impedance. Let's try that again, with feeling , Resonance is Not VSWR. Resonance can be at minimal vswr, or not. Minimum vswr can be at resonance, or not. The two are interrelated but mutually exclusive and separate terms.

We currently have cool toys like rig expert and nano vna. but unless you anticipate frequently tossing wire around the property even the $99 VNA is overkill.

So with those definitions and links in place:
Place a dummy load on the output of the amplifier and without plugging it in or turning it on check the vswr between the radio and the amp. This first easy step will prevent issues later. Any bypass vswr has to be eliminated. Methods are a swamping resistor(s), constant impedance attenuator (3Db "T" pad) , or a lump constant tuned circuit ( capacitor/inductor network) Once the vswr barely if at all registers , move on .

Next, turn the amp on and with reasonable input observe the input vswr with the amp output into a dummy load. Again if this circuit displays significant vswr a swamping resistor(s), constant impedance attenuator (3Db "T" pad) , or a lump constant tuned circuit ( capacitor/inductor network) are needed to adjust the input vswr across the intended range of operation. I don't mean to gloss over all that this entails because you simply asked "where does the vswr meter go" . What you didn't know is that this opens a YUUUUUge can of worms.

So now you have a radio that drives an amplifier without seeing significant vswr. You have some significant output at the exit of the amplifier. What next?

A brief look at drive and efficiency.
One watt in = 10 watts out
Two watts in = 20 watts out
Three watts in = 30 watts out
Four watts in = 40 watts out
....

This is "linear" behavior.

14.49A @ 13.8V for 100 watts output.
This amplifier is 50% efficient. Take my word for it or do the math :)

Fully modulated AM output is four times the quiescent carrier. So four watts carrier fully modulated is 16 watts.
Now do you understand why a pair of 2sc455's or even 2sc2290's only need 2-3 watts of drive?

So the easiest way to establish drive level is watts input/output vs current draw. Simply put if the next amp you draw is only producing 25% more output than the last amp you drew it's time to back off. How much you back off depends on how deep your pockets are.

Okay now we're at the voodoo where resonance does not equal resistance. Resonance is NOT necessarily at 1:1 vswr.
A dummy load has a perfect 1:1 match but isn't much of antenna by design. Off Center Fed Dipoles are regularly fed at a 200 ohm point and are great antennas. Several constructions of wire antennas are resonant at frequency and exhibit feed point impedance in the several thousands of ohms.

From the above link to the antenna handbook find the chapter on matching sections. If the dimensions of the antenna make any realistic sense IE: 9 foot whip, 18 foot dipole, or any reasonable fraction or multiple there of you can continue.
You have two choices here, fool the amp into seeing a flat match with a tuner or fix the antenna feed point. The alternative is to place the tuner at the antenna feed point but not always convenient.
The best of the two choices as to fix the feed point so that your coax or other feed line isn't confused and either radiating or heating.
Mismatches under 2.5:1 (opinion) result in such minimal losses that placing the tuner at the amp output is acceptable if not ideal.

so the TLDR version as promised. An even shorter version follows this one.
Both goesinta and goesouta vswr/power meters.

Resonance does not equal vswr

For solid state devices an amp meter really really really helps set appropriate drive levels.

Do not over drive the poor beastie. You will let the smoke out.
If you're getting 100 ish (peak reading)output for around 15A @ 13.8V, out for 3 watts in on AM with a tone or whistle with a 25-30 dead carrier out of a random pair of magic smoke containment devices be happy.

12-14V DC MOSFET amplifiers are an absolute minefield.
I avoid them like my future ex-wife.

Amp bypass and amp input vswr are two separate circuits.

If the amp and the antenna are at or near 50 ohms the feed line becomes practically invisible save for it's losses.

It's not rocket surgery but it is brain science.

TLDR:
Both
Don't overdrive it or gawd will kill a kitten.



I thank you for all the info although I am clumsy and not technical at all and would probably f up anything I try that is explained to me LOL and hence the reason for asking here. I know I am not saying everything correctly and many techs are nit picking the way I am saying things. Thats why I was just looking for a short answer of where it goes for adjusting the SWR, in my terms. I do believe I saw that video before years ago when I was searching about it, didn't really catch on as again I am not that into that stuff. Just looking for quick easy answers. I have a SWR meter and just want to know where it goes with an amp in line. I read from the biulder that he said lower than 1.5 SWR into the amp, so thats why I asked if it goes just at the radio input side of the amp. I run a galaxy dx979 with it doing around 25ish peak right now. My last amp was an old TS 500DX non variable and lasted 17 years before I had to sell it, and half that time I didin't even know what SWR was LOL. Thanks for the info though, much appreciated.
 

Cabover Bob

567 on the west side
Nov 17, 2020
381
613
103
111
Lots of good info here. What is the consensus on an E.F. Johnson CB Matchbox 250-49 tuner ? I know that it's '50's technology, but so are most of the meters being discussed here.

Suitable for a mobile installation ?

Todd
 

kopcicle

Sr. Member
Feb 17, 2016
2,073
3,303
273
E.F. Johnson CB Matchbox 250-49 tuner
Weak, a serious, stock, as in a proper uPD858 chassis, Realistic TRC-449/Robyn 510D/Early Grant, may eventually damage it. When used between a "driver" as in a 2-3 watt AM, no more than a 12 watt SSB output it will last for years and be a great addition.

I'm still a bigger fan of curing the problem , if one exists, at the antenna.

If on the other hand the issue is at the input to an amplifier fix it there.

I have always felt that these devices were a solution in search of a problem. I'm more in favor of curing the cause, not treating the symptom.

just my $0.02 worth ...


...and where's my change ?
 

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