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Author Topic: What advantage has a remote tuner?  (Read 2950 times)
KD4SBY
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Posts: 223




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« on: January 15, 2012, 08:09:27 AM »

I am wondering what the advantages are of having an remote tuner versus one right behind the TX? Does the remote not has the tendency to match its input (the cable) to the antenna which not necessarily may mean that your TX is matched to the antenna? With a tuner in the shack you at least know that the TX is matched to whatever is connected to the output of tuner, is that true with a remote one? Or do you ideally need two tuners, one inside and one at the antenna site to get an ideal match?
Any comments?
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WX7G
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« Reply #1 on: January 15, 2012, 08:25:45 AM »

With a tuner at the antenna there is no mismatched tranmission line to exhibit increased loss due to a high VSWR. The coaxial transmission line between the tuner and the transmitter is operated at a low VSWR (near 1:1) and exhibits no extra loss. 

With a tuner at the transmitter the transmission line between the antenna and the tuner might be operated at a high VSWR and exhibit increased loss.

Only one tuner is needed.
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M6GOM
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« Reply #2 on: January 15, 2012, 09:11:33 AM »

As above. On my inverted L, the SWR can reach over 50:1. The losses over 100ft of RG213 would be over 8.5dB so out of the 100W my transceiver was putting out, only 13.85 would reach the antenna if I used a tuner at the rig end. By using a SGC230, virtually 100W makes it into the tuner and the only losses are the tuner losses.
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KD4SBY
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« Reply #3 on: January 15, 2012, 12:54:01 PM »

Got the idea. With other words, with a tuner at the antenna the TX sees a correct match at its output and the SWR = 1. Full power is now applied to the tuner, (minus any cable losses), which in turn matches the antenna. Since it is so close to the antenna, cable losses are minimum, even with some SWR. The end result is more power into the antenna in this setup, even if all the components are the same as where the tuner is at the TX. Correct?
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WB2WIK
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« Reply #4 on: January 15, 2012, 06:39:58 PM »

You pretty much have the idea.

If the line was matched to the antenna, line losses would be minimized and you would have no reason to use a tuner at all.

When there's a mismatch, line losses increase; using a tuner at the antenna rather than at the transmitter create a good match for the line, so line losses are still minimized, as they would be with a normally matched antenna.

The "difference" in efficiency is based purely on transmission line loss.  If the line loss were zero, there wouldn't be any difference, either way.
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KD4SBY
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« Reply #5 on: January 16, 2012, 06:14:56 AM »

OK, than  I understand it right. In my situation I have a tuner at the TX, and abt. 130 ft of RG8 cable to the antenna. I have been able to tune my antennas pretty good and can get a SWR around 3-4, sometimes below 2 directly at the TX, without the tuner, on 7 bands, depending on the frequency. The tuner brings it down to around 1.3 on many frequencies, and never above 2 on any of the frequencies used.
Looks that it would not be worth the expense of having a remote tuner. That was the information I was after. Thanks fellows!
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K2QB
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« Reply #6 on: January 16, 2012, 06:21:27 AM »

To M6GOM's reply...8.5db over 100ft?Huh What frequency are you operating at..1Ghz? The loss per 100ft at 10Mhz is in the area of .5db.
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N3OX
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« Reply #7 on: January 16, 2012, 06:36:44 AM »

To M6GOM's reply...8.5db over 100ft?Huh What frequency are you operating at..1Ghz?

No... the very high SWR on the feedline increases the losses a lot.

Quote from: M6GOM
On my inverted L, the SWR can reach over 50:1.

It's easy to get extraordinarily high SWR on some bands for multiband antennas, and when faced with a 50:1 or 100:1 SWR, especially at a bad phase angle, losses can get extreme.  I run a half wave 40m vertical here, usually with a matching network at the base.  I did an experiment where I switched to direct coax feed tuned it with a tuner in the shack instead.  I used VK1OD's transmission line calculator and the EZNEC prediction for the vertical's base impedance to come up with about 10dB predicted coax loss in less than 100 feet of mixed RG-8/X and RG-213.  I then did an actual measurement of the signal level drop, because it was easy for me to switch back and forth between direct feed with the shack tuner and the 40m network at the base of the antenna:

http://n3ox.net/projects/sixtyvert/fortynet_lg.jpg

The 10dB predicted number was about right as measured on some broadcast stations up in the phone portion (steady carriers)

Extreme mismatches can cause extreme loss.  5:1 or even 10:1 SWR isn't usually too bad, but it's easy to get 50:1 SWR or even 100:1 SWR or 200:1 SWR when you have a short antenna with a low feedpoint resistance and a bit of reactance.  Low resistance antennas with large reactance are the worst, like a dipole used well below its fundamental resonance or direct feed of a small loop.  Here's a plot of SWR  on LMR-400 vs. reactance for three different resistances: 12.5 ohms, 50 ohms, and 2500 ohms:

http://n3ox.net/files/VSWRX.jpg

Adding a few hundred ohms of reactance to a 2500 ohm load doesn't increase the reflection from the load much, so the SWR is nearly flat at 50:1.  But at 12.5 ohms?  250 ohms of reactance and you're well over 100:1 SWR.   A 40m dipole used on the low end of 80m might be something like 10-j1000, which is nearly 1200:1 SWR.  With such a horrible mismatch you will see 10dB loss in 25 feet of RG-213
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
AA4HA
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Posts: 1378




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« Reply #8 on: January 16, 2012, 07:21:45 AM »

The only downside I have ran into with remote tuners is the requirement to get power and in some cases, control signals out there. Ideally it would be some sort of DC powered tuner that could run off of a battery, recharged by a solar panel mounted right on the case of the tuner and it would auto detect the transmitting frequency without the use of a control cable. That way you would not need to provide for transient surge protection on the power and control cable, just on the feedline.
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
K2QB
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« Reply #9 on: January 16, 2012, 12:50:41 PM »

I stand corrected...I didn't read his post correctly..... Roll Eyes
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N4JTE
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« Reply #10 on: January 16, 2012, 04:07:33 PM »

Just one more note to the symphony, moving tuner to antenna good thing, lousy antenna next to tuner bad thing.
Bob
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WA4FNG
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« Reply #11 on: January 16, 2012, 07:44:44 PM »

OK, than  I understand it right. In my situation I have a tuner at the TX, and abt. 130 ft of RG8 cable to the antenna. I have been able to tune my antennas pretty good and can get a SWR around 3-4, sometimes below 2 directly at the TX, without the tuner, on 7 bands, depending on the frequency. The tuner brings it down to around 1.3 on many frequencies, and never above 2 on any of the frequencies used.
Looks that it would not be worth the expense of having a remote tuner. That was the information I was after. Thanks fellows!

I don't think you have that right.... you may be matching it at the TX with the tuner, but the SWR between the tuner and the antenna could be very high leading to signal loss in the line. In the situation you're describing you WANT the tuner at the antenna because your trying to use one antenna on 7 bands AND you're using coax. Sounds like you have a mismatch at the antenna on most or all of those bands. Even though the tuner makes the rig happy, it's also masking the loss your getting in the feedline. The only reason to put the tuner at the TX is if you are using open wire balanced feeder or extremely low-loss coax.
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KD4SBY
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Posts: 223




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« Reply #12 on: January 17, 2012, 06:56:44 AM »

WA4FNG - You are right in your reasoning, wrong in your assessment of my situation. I realize that I neglected to mention that I first tuned my antennas directly at the antenna site, using an MFJ259B Antenna Analyzer, and I got the SWR readings from this instrument at that time. These figures where verified then  at the TX site using the same instrument but now using the coax feedline. Sorry about that.
BTW The antenna is a coax fed Hustler 4BTF with 3 bands added using end-fed wires. (Go to my posting on this subject to see how I did this. It is a easy way to add other bands to a vertical and it works very well.)
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