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Author Topic: Tuner and Amplifier Connection Order  (Read 4370 times)
AK4SK
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Posts: 150




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« on: January 07, 2013, 08:19:22 AM »

I have a rookie question. Are antenna tuners always the last piece of gear before the feed line going to an antenna? In other words they are always downstream of any amplifier being used, correct? Why is this? Why can't a tuner be between the transceiver and amplifier?

Thanks,
Chris
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WB2WIK
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« Reply #1 on: January 07, 2013, 08:27:27 AM »

It could be, but then it would only be "tuning" the input to the amplifier.  Sometimes, that helps.  But that has nothing to do with matching the antenna.
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N4CR
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« Reply #2 on: January 07, 2013, 10:17:56 AM »

I have a rookie question. Are antenna tuners always the last piece of gear before the feed line going to an antenna? In other words they are always downstream of any amplifier being used, correct? Why is this? Why can't a tuner be between the transceiver and amplifier?

The primary purpose of your antenna tuner is to provide a lump sum impedance that matches the impedance of a transmitter to the impedance of a load to attain maximum power transfer between the two. To accomplish that for a linear amplifier, it has to sit between the linear amplifier and the antenna.

Most amplifiers already have a tuned input circuit so there is no need to add an additional tuner since maximum power transfer from your transceiver to the amplifier is already accomplished.

A secondary purpose is that it also matches the antenna during receive (the signal) and the receiver (the load), so this match work in both directions. If your transmitter is tuned to 50 ohms and your receiver is tuned to 50 ohms, these occur at the same place.

This is one reason that it is suggested that you tune your amplifier into a dummy load (which sets it to 50 ohms) and then tune your outboard tuner to match to the antenna since this also will match the antenna to your receiver when you are not transmitting.

Transistorized linear amplifiers have a fixed output impedance and generally require a tuner to follow them or they will not attain full output power.

Tube amplifiers have a tuning section (very similar to your antenna tuner) following the tubes which servers the very purpose of matching the output impedance of the tubes to the impedance of the load. If your antenna system presents a reasonable impedance of less than about 3:1 to a tube linear, then the tune up process of the amplifier can be the antenna tuner and you don't need another one.

For highly mismatched systems, the tube amplifier will not be able to tune because the mismatch is too large and an additional tuner is required.

Every place you add equipment in your coax sequence, it introduces some loss, so putting a tuner in line where one is not needed simply steals some signal or output power without giving you anything in return. If you bypass your tuner and your amplifier will still tune up, you are good to go.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
AK4SK
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« Reply #3 on: January 07, 2013, 01:14:42 PM »

Thanks to you both. I guess I was thinking about it wrong. I knew that common practice was to have the tuner last but I didn't know why. I was thinking that the tuner could "see" the antenna through the amp but it sounds like a tuner placed between the radio and amp just sees that amp as a 50 ohm load. I don't have an amp yet so I was trying to figure out if I would need a tuner rated to a higher power level to pair with an amp.
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N4CR
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« Reply #4 on: January 07, 2013, 01:43:25 PM »

Thanks to you both. I guess I was thinking about it wrong. I knew that common practice was to have the tuner last but I didn't know why. I was thinking that the tuner could "see" the antenna through the amp but it sounds like a tuner placed between the radio and amp just sees that amp as a 50 ohm load. I don't have an amp yet so I was trying to figure out if I would need a tuner rated to a higher power level to pair with an amp.

Yes, the radio sees the amplifier input as a 50 ohm load. If your radio has a built in tuner, you would turn it off because it's already matched and the radio's internal tuner can only steal power from you and give you nothing in return when that is the case.

Since the antenna tuner goes after the amplifier, you'll need a high power tuner.
« Last Edit: January 07, 2013, 01:51:59 PM by N4CR » Logged

73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
KE3WD
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« Reply #5 on: January 07, 2013, 02:32:11 PM »

No such thing as QRO on the cheap, but one can get there without breaking the bank account with frugal purchases. patience and a bit of good old amateur ingenuity. 


73
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WB2WIK
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« Reply #6 on: January 07, 2013, 03:08:59 PM »

I think it always pays to use a high powered tuner, even for low powered operations.

The larger (high power rated) tuners nearly always have less insertion loss, and offer improved performance at any power level.
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KE3WD
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« Reply #7 on: January 07, 2013, 03:58:19 PM »

I think it always pays to use a high powered tuner, even for low powered operations.

The larger (high power rated) tuners nearly always have less insertion loss, and offer improved performance at any power level.

Agreed.  As soon as I could, I started using qro matchboxes exclusively and haven't looked back. 

73
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AK4SK
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« Reply #8 on: January 08, 2013, 06:31:05 AM »

Thanks again for the help.
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KD4SBY
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« Reply #9 on: January 08, 2013, 08:17:49 AM »

To expand on the original question, how do you tune a system when a tube type amplifier is connected to a tuner? I have the following setup: Solid state 100W Transceiver - SB-200 Amp - SA-2040 1KW Tuner - SWR meter - Ant.
Starting from scratch, what is the correct way to get on the air? (Regardless of Band used)
Also, can I use an auto tuner between the Transceiver and the Linear? Or should I not use one in that case?
(I use the auto tuner when using the Transceiver barefoot and leave it in the chain if possible.)
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KM3F
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« Reply #10 on: January 08, 2013, 08:44:32 AM »

Tune for best SWR before you put amplifier on line.
Amp on line at low drive to get the tune and load setting first.
Then fine tune everything at full drive.
Record the settings.
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KA1MDA
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« Reply #11 on: January 08, 2013, 09:33:14 AM »

I have the following setup: Solid state 100W Transceiver - SB-200 Amp - SA-2040 1KW Tuner - SWR meter - Ant.
Starting from scratch, what is the correct way to get on the air?

The SWR meter should go between the amp and the tuner, such as below:
100W Transceiver - SB-200 Amp - SWR meter - SA-2040 1KW Tuner - Antenna
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KD4SBY
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« Reply #12 on: January 08, 2013, 12:34:02 PM »

Got all that. Now back up several steps. Assuming I have never owned a SB-200 Linear and a tuner, and now I like to put my Transceiver on the air using both of them. What step by step procedure do I perform?
(I like to know that, because I am new to Tube Linears and am not quite sure how to tune and load them.  Do I understand it right that I use the load-tune adjustments to get to the point that varying the Load Adjustment will not significantly change the RF output with the Tuning knob? Or do I look at Plate Currents?
Also the tuner uses a roller inductor and two capacitors, what is the best combination to aim for to begin with?)
Comments anyone?
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WB2WIK
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« Reply #13 on: January 08, 2013, 01:33:59 PM »

Got all that. Now back up several steps. Assuming I have never owned a SB-200 Linear and a tuner, and now I like to put my Transceiver on the air using both of them. What step by step procedure do I perform?

As stated above, the SWR meter goes between the amp and the tuner, not between the tuner and the transmission line to the antenna.

I'd always recommend making tuner adjustments with low power (barefoot, and preferably with that turned down to 5W or something), and null the SWR to perfect, or as perfect as possible.  Then, increase power and add the amp and the tuner should not require re-adjustment at all.

Quote
(I like to know that, because I am new to Tube Linears and am not quite sure how to tune and load them.  Do I understand it right that I use the load-tune adjustments to get to the point that varying the Load Adjustment will not significantly change the RF output with the Tuning knob? Or do I look at Plate Currents?

Plate current doesn't tell you anything particularly useful, although it's nice to look at it and see that "nothing's wrong," such as pegging the meter with a current reading that's drastically higher than it should be.  Using a steady (CW) carrier, tune both PLATE (or TUNE) and LOAD controls for absolute maximum output power: These interact, so it's a reiterative process.  Once max power is achieved and further adjustments yield no improvement, advance the LOAD control slightly (almost always clockwise to increase loading) while watching GRID (not plate) current, to decrease grid current slightly.  Then stop, and "log" those control settings for future reference, which makes it a lot easier and faster to tune up next time on that band and approximate frequency.

If I'm not using a tuner at all, I usually "tune up" a new tube amplifier on a few frequencies per band with the real-world antennas I use, when the bands are "dead," such as tuning up on 160m and 80m at noontime, or 10-12-15m at midnight, etc.  40m may never be dead, but there are periods of shortened propagation and less activity (often midday), so I'd pick one of those times, rather than tuning up at night when the band's wide open.  The reason for this, although the process may take a whole day to complete, is to minimize interference to others while experimenting.

Now, if I am using a tuner and it can be adjusted to create a "perfect" or nearly perfect match (VSWR = 1.0), then the amplifier tuning process can be made much easier: Tune the amp into a good 50 Ohm dummy load at a few frequencies on each band, any old time you want to do that.  Log those settings for reference.  Then, once the antenna tuner is adjusted for a nearly perfect match, just switch from the dummy load to the tuner and the amplifier should already be tuned with no further tuning required. Wink


Quote
Also the tuner uses a roller inductor and two capacitors, what is the best combination to aim for to begin with?)
Comments anyone?

Always the settings that use the minimum inductance to provide a good match.  If you can't tell which setting is "min" and which is "max" by looking at the front panel, I take the cover off and look inside to see. Smiley
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KD4SBY
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« Reply #14 on: January 08, 2013, 05:36:25 PM »


I'd always recommend making tuner adjustments with low power (barefoot, and preferably with that turned down to 5W or something), and null the SWR to perfect, or as perfect as possible.  Then, increase power and add the amp and the tuner should not require re-adjustment at all.


Now, if I am using a tuner and it can be adjusted to create a "perfect" or nearly perfect match (VSWR = 1.0), then the amplifier tuning process can be made much easier: Tune the amp into a good 50 Ohm dummy load at a few frequencies on each band, any old time you want to do that.  Log those settings for reference.  Then, once the antenna tuner is adjusted for a nearly perfect match, just switch from the dummy load to the tuner and the amplifier should already be tuned with no further tuning required. Wink

1. I use a power level of a 15-20W to tune up. This level is available on my Transceiver by pulling a certain pin to ground at its connector for an auto tuner. (Which I also have, but it is rated only for 200W)
2. That sounds like a good idea. I happen to have a 1200W Dummy Load, so I can use that info to simplify things.
Thanks fellows!
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