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Author Topic: External Tuner vs Radio's Internal Tuner  (Read 3278 times)
KB1TJY
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Posts: 257




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« on: December 21, 2012, 06:35:48 PM »

What is the real advantage to using an external Antenna Tuner such as the Palstar AT2K over the automatic tuner provided with most rigs?

Many thanks!

Lyman
KB1TJY
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K7KBN
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Posts: 2817




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« Reply #1 on: December 21, 2012, 06:55:24 PM »

The range over which the unit can match.  Many built-in "tuners" can cope with up to something like 3:1 mismatch.  Anything worse than that will kick it out of line.

A decent MANUAL tuner can handle much worse mismatches.
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73
Pat K7KBN
CWO4 USNR Ret.
VA7CPC
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Posts: 2395




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« Reply #2 on: December 21, 2012, 08:46:40 PM »

The range over which the unit can match.  Many built-in "tuners" can cope with up to something like 3:1 mismatch.  Anything worse than that will kick it out of line.

A decent MANUAL tuner can handle much worse mismatches.

Even many automatic tuners!

.            Charles
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KB1TJY
Member

Posts: 257




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« Reply #3 on: December 21, 2012, 09:15:46 PM »

The range over which the unit can match.  Many built-in "tuners" can cope with up to something like 3:1 mismatch.  Anything worse than that will kick it out of line.

A decent MANUAL tuner can handle much worse mismatches.

Even many automatic tuners!

.            Charles
Thank you both, greatly appreciated!

Lyman
KB1TJY
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M6GOM
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Posts: 955




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« Reply #4 on: December 22, 2012, 08:30:04 AM »

I'd just like to throw my two penneth in.

Depending on the SWR and the length of coax you're using, the losses due to the SWR can be quite horrific. I am not a fan of ATUs because of this. A far better solution is an antenna coupler such as a SGC230. Not only will you put more power into the antenna, you'll hear more too as losses are reciprocal so a 10dB coax loss affects both transmit and receive.

A friend of mine changed from an ATU in his shack to an antenna coupler at the feedpoint of his doublet. He has worked more with 100W from the transceiver than he ever did with 800W and he can hear far more too.
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AA4PB
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Posts: 12905




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« Reply #5 on: December 22, 2012, 08:44:34 AM »

I agree. If the SWR on a **coax** feedline is greater than 3:1 then you need to consider putting a tuner out at the antenna.
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N4CR
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Posts: 1672




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« Reply #6 on: December 22, 2012, 12:20:17 PM »

I agree. If the SWR on a **coax** feedline is greater than 3:1 then you need to consider putting a tuner out at the antenna.


Or use a lower loss feed line.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
W4RS
Member

Posts: 64




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« Reply #7 on: December 25, 2012, 02:05:15 AM »

i have always been told" buy the best coax you can find" for 90% of your power will radiate out of it! just kidding, but the coax does not have a forever life. i use external tunners, the nye 4-v they are built to take care of mismatches. i don't use the built in antenna tunners, except in mobile use. a easy way to check coax i found is a 50 dummy load at one end, and a ant anilizer like the mfj 259. see what the resistance is. you can check hard line the same way!

jim w4rs du3/w4rs
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G3RZP
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Posts: 4742




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« Reply #8 on: December 25, 2012, 03:42:35 AM »

One quick way is to disconnect the coax and measure SWR. If it isn't very high, the coax is bad.
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WB6BYU
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Posts: 13353




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« Reply #9 on: December 25, 2012, 11:43:47 AM »

Quote from: W4RS
...a easy way to check coax i found is a 50 dummy load at one end, and a ant anilizer like the mfj 259. see what the resistance is.


If you put a dummy load on the far end and check the SWR (or RF resistance), even a lossy feedline
will still look like 50 ohms.  That is NOT a good check for losses unless you use a power meter at both
ends.  A low SWR in a system is often an indicator of HIGH losses in the coax.

Instead, use Peter G3RZP's approach:  disconnect the antenna from the far end of the coax (or use
a band where you expect the SWR to be high) and check the SWR.  The higher the SWR, the lower
the loss of the cable.  Because the far end is disconnected (or shorted, if that is easier) the SWR
at the antenna is high, and it should be high also at the rig end unless the cable is lossy.  If the
SWR is 3 : 1 at the rig (or better) in that case, consider replacing the coax.

I use this with my triband yagi:  I check the SWR on 12m or 17m, and if it is too low then the
coax is too lossy.  Using a band where the SWR is high makes it easier because I don't have
to climb the tower to disconnect the coax, especially if I were smart enough to check the SWR
on all bands when I first put up the antenna, then checking it periodically will tell me if the
coax has degraded.
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N3JBH
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Posts: 2358




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« Reply #10 on: December 25, 2012, 12:02:30 PM »

Big fan here as well for open wire feeders. Palstar tuner's not as much a fan of any more. And there no way in heck i use a palstar balun oh no never ever again been screwed over there from great old Paul. But hey still recommend open wire/ ladder line feeder. 
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G3RZP
Member

Posts: 4742




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« Reply #11 on: December 25, 2012, 12:07:43 PM »

A good old fashioned tuner as per ARRL handbooks from the 1950's works very well. Yes, it's not as convenient as a modern 'sit on the desk tuner' and a 'balun' but it works rather better with ladder line feeders..
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W5DXP
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Posts: 3630


WWW

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« Reply #12 on: December 26, 2012, 07:35:35 AM »

Big fan here as well for open wire feeders.

One nice thing is those feeders can be tuned for a 50 ohm SWR close to 1:1. For instance, a 9:1 SWR on 450 ohm ladder-line allows a particular length of feedline to present 50 ohms at the shack thus eliminating the need for any tuner.

http://www.w5dxp.com/notuner.com
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
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