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Author Topic: Manual antenna tuner and vertical base tuning  (Read 942 times)
VK1KHV
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Posts: 73




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« Reply #15 on: August 31, 2009, 01:49:16 PM »

250 pf on the output. maxed on the input at 480pf. 5uh aint bad i dont think
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N3OX
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« Reply #16 on: August 31, 2009, 02:05:32 PM »

Sounds like it\'s going to work fine...

480pF 6kV is a lot more suitable than the capacitor Tom was assuming... which based on the stated 500 ohms, would be about 175pF.

A lot of people are trying to load much shorter verticals with much less 160m-capable tuners.  And you\'re still doubling the capacitive reactance of the antenna by adding the output cap to it.

It\'d still be better with a series inductor but you\'ll have a comfortable margin against arcing the cap with the tuner setup.

If you\'re running high power  and are long winded (or run RTTY or something) you should worry about tuner coil heating... even 0.5dB is kind of a lot of heat then... and it\'s boxed in a case instead of out in the breeze.

It seems like a reasonable compromise to me with 480pF 6kV caps.
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
N3OX
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« Reply #17 on: August 31, 2009, 02:07:09 PM »

Wait, 250pF on the output or the input?  On the output you\'re going to start pushing it (assuming 1500W... I guess we don\'t know how much power you intend to run) but that doesn\'t sound like that\'s the matching solution...
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
W9OY
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« Reply #18 on: September 01, 2009, 08:36:45 AM »

Are you going out to the tuner and tuning it when you switch bands?  

If so just use the vertical to support an inv-L wire on 160 and a knife switch or something to switch between the 160-L and the 3/8 80M.  

You could match the L on its own to the coax, and use a coax relay to switch the coax between the L and the tuner that way you would be able to switch 160 and one other band (what ever you have the tuner set to) from the shack

OR you could have 2 wires (one for 160 and one for 40) supported from the 80M vertical and have separate matching networks for each of 3 antennas 160, 80, 40, and use a coax switch to switch between any of the 3 bands from the shack and leave the palstar for another project.  For 40M I suggest a 1/2 wave vertical end fed with a parallel network, and for 160 the inv-L with a hairpin coil across the feed point.  So to make this work you would need a 3 postiion coax switch, a coil for the 160 antenna (piece of #10 wound around a coke can will self support and you can adjust it by spreading or collapsing the lenght of the coil) and a coil and cap for the 40M antenna  

All verticals use a common radial field

This is how I have my verticals configured.  

73  W9OY
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VK1KHV
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Posts: 73




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« Reply #19 on: September 01, 2009, 04:22:34 PM »

the little calculator for the T.

says
INPUT 480pf
COIL 4.9mh
OUTPUT 226pf

the tuner as i said is 480pf on output and input and 26mh coil
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VK1KHV
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« Reply #20 on: September 01, 2009, 04:29:42 PM »

i would need to go out there to move to T wires anyways os yes i would be going out there to move the dials.

but once i get the right settings just make a mark on the tuner.

n3ox: im running 1200w pep max 600 cw max

it seems to me like it might work.
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VK1KHV
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« Reply #21 on: September 02, 2009, 02:24:44 AM »

i built a coil from that calculator.

says Q 1100 which i know is way to high but it will be decent maybe 600ish

its 1/4 (6.35mm) copper pipe air wound
21 turns 150mm d 250 l

28uh

put the meter on it today it resonated at 12ohms +j1

seems right seeing ythere is 100 40 meter radials under it.

so im assuming my best bet wound be to put the tuner in line with that. and it will give me a 50 ohm match?

only thing im trying to figure at the moment is how do i do a band switch.

switching the coil out so i can use the vertical on 80 just with a little capacitance.

dunno any ideas?
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N3OX
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« Reply #22 on: September 02, 2009, 07:17:53 AM »

"so im assuming my best bet wound be to put the tuner in line with that. and it will give me a 50 ohm match? "

Or you could detune the antenna a little high in frequency use a shunt inductor between the coax center conductor and ground.  This gives you a complete L-network to match to 50+j0.  W9OY suggested this too, suggested using a "hairpin coil," a term borrowed from "hairpin" or "beta" matching on yagis...

If you detune the antenna so that it reads 12-j21 at your frequency of interest, and put a 2.5 microhenry inductor (+j28 ohms) between the coax center and ground, the impedance seen by the coax will be:

12-j21 in parallel with +j28, which according to Google Calculator is:

1 / ((1 / ((12 ohms) - (i * (21 ohms)))) + (1 / (i * (28 ohms)))) = 48.746114 - 0.435233161 i ohms

You have to use "i" in Google Calc instead of "j" ;-)

This is what I do for my 60 foot vertical.  

http://n3ox.net/projects/stepperswitch/160_match_lg.jpg

The big red coil is the loading coil and the small natural copper coil is the "hairpin" or shunt coil.

I use a computer controlled switch to switch mine:

http://n3ox.net/projects/stepperswitch/

Doesn't sound up your alley in terms of simplicity ;-)  But if you had a big wafer switch like that, you could just wire up your networks and switch it by hand.  

You just need two poles of switching... one fairly low voltage one to switch the 50 ohm side from your 160m matching network to the tuner or whatever, and one high voltage side to switch the antenna to the various networks.  Of course, like my switch, both could be high voltage.

Maybe you could sell the Palstar and buy some vacuum relays to switch home-made networks in and out given that you are very close to having 80 and 160 done.  

I use a program called L_TUNER from here a lot:

http://zerobeat.net/G4FGQ/page3.html#S301%22  

Just cook yourself up a 40m matching network and switch with some relays?

I dunno... There are lots of ways to go with this.  I really like having pre-tuned networks ready to go.  Relays are the simplest remote solution.  My rotary switch is much more complicated but also ended up being a lot cheaper than the large number of vacuum relays I would have needed.

But a manual band switch could be really easy if you can find a big two-pole wafer switch like the one inside my stepper switch.

73
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
W4HV
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« Reply #23 on: September 08, 2009, 11:51:23 AM »

On that switch problem...if you don't mind manual switching. Go to the farm supply store and get an electric fence switch..they are hust a nice big knife switch and work very nicely with rf...Real cheap and real easy to configure anything you need to manually switch in inductors or caps with a big expense!
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