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Author Topic: Why use a tuner with Ts-520?  (Read 1526 times)
KJ4RQV
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Posts: 130




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« on: January 30, 2013, 12:32:16 PM »

I have figured out my tune up problems with my Kenwood 520 thanks to the help I have received here and elsewhere so thanks to all. I have ordered a new driver tube as it is weak and will be replacing it.

Now, a general question about these hybrids. If I am understanding them correctly when adjusting the plate and load we are adjusting to achieve best power and resonance to the antenna for the frequency we will TX on.

If this is correct, what does an antenna tuner actually do for this radio type? I understand the matching purposes of the tuner in general but does the tuner just fine tune the plate and load set up on the hybrids?
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AA4PB
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« Reply #1 on: January 30, 2013, 12:49:01 PM »

A tuner is only useful with a tube final (plate and load controls) if the antenna impedance is beyond the matching capability (about 3:1 SWR) of the final tune circuit.
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WB6BYU
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« Reply #2 on: January 30, 2013, 12:49:47 PM »

The output tuning and loading controls, along with the fixed output coil, limit the range of
impedances that can be matched on each band.  Often the limitation is that loading
capacitor is too small to match low impedance loads.  (One of the old Johnson rigs, for
example, was rated to match 40 to 600 ohms:  if your SWR on 50 ohm coax was 1.5 : 1,
for some lengths it would be less than the 40 ohm minimum.)

If the outboard tuner is one that has limited range, it might not add any further capability.
But there will be some load impedances that will be out of the range that the TS-520 can
properly load, and for those you would want to use an external tuner.  (Or fix the antenna.)
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AA4PB
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« Reply #3 on: January 30, 2013, 01:01:32 PM »

The TS520S is specified for an load impedance of 15 to 200 Ohms. It should be fine for any resonant dipole or similar antenna.

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KJ4RQV
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Posts: 130




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« Reply #4 on: January 30, 2013, 01:23:02 PM »

Thank you all!

Makes sense, I was over looking the obvious.
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AD4U
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« Reply #5 on: January 30, 2013, 04:13:18 PM »

Make that to say any 50 ohm resonant antenna, FED WITH 50 OHM COAX.  None of the tube type rigs made in the past 50 years with a pi-net will operate successfully directly into open wire feeders.

Dick  AD4U
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W6EM
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Posts: 812




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« Reply #6 on: January 30, 2013, 04:16:19 PM »

Tube amplifiers are, by nature, high impedance.  Plate impedances in the 4000 ohm area are typical.  PI networks were the choice in most all transmitter designs.  PI networks are capable of transforming a very high input impedance to a very low output impedance.  Whereas, T networks typically will match up to a few hundred ohms to a few hundred ohms or less and are usually symmetrical, meaning the input and output capacitors are most often variable capacitors of the same range and rating.

Trying to load a PI network into a typical tuner with a T network would produce quite a range of possibilities to achieve a satisfactory match.  Worst of all, a lot of confusion and needless extra work going back and forth.  It also might stress your finals a tad until you get everything just right.  :--)

73,

Lee
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AC5UP
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« Reply #7 on: January 30, 2013, 04:19:59 PM »

Make that to say any 50 ohm resonant antenna, FED WITH 50 OHM COAX.

True enough regarding an open wire feeder, but why so selective on the coax impedance?

Betcha' a TS-520 would load a dipole fed with RG-59 or RG-11 just like it was still 1978 and the bands were wide open.............!
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KJ4RQV
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Posts: 130




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« Reply #8 on: January 30, 2013, 04:57:42 PM »

I think that the ONLY tuner I will consider is a Kenwood from that era!
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N8NSN
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« Reply #9 on: February 02, 2013, 08:50:16 AM »

Only time I use a tuner with my FT-101 hybrid is if I'm using a "random" antenna on a given band. Say like a 30 foot vertical with a random counterpoise, on any band 40 - 10 meters. To achieve something resemblant of efficient: I tune the radio into a heathkit cantenna since it represents a 50 ohm load. If the rig has an SO-239 connector on the rear apron, chances are it'll be happy with an impedance between 40 and say 90 ohms. given the era, 50 ohms is a nice mark to go with, and 50 ohm loads are commonly available. Then, place the tuner in line. Rig - SWR meter - Tuner - Antenna. Set both caps on the T network to 50%, adjust inductor for best receive level, key xmtr in tune mode and observe SWR, tweak the caps for best dip in SWR. Usually doesn't take a lot of tweaking as that peak in recieved signal is usuallr representative of things being fairly close to the 50 ohm load the radio's pi network was already set for.

If you want to run the 600 ohm near no loss parallel feed to an balanced system - build a link coupled tuner to resonate the system. That's my favorite choice where parallel feeders can have a system with a 20 or higher to 1 SWR and still represent nearly zero loss in feed lines. Unbalanced Feed-line mismatches are where systems lose most of their capabilities.

Never overthink it :-) & have loads (intended pun) of fun.
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