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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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26th Feb 2023, 1:34 pm | #1 |
Hexode
Join Date: Dec 2018
Location: Lugo, Spain
Posts: 477
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Link coupled Z match
Nearing the end of a build here of a Link coupled z match from bits and bobs.
Question , will it work with just a single VC across the balanced line o/p ?. An amateur on you tube posted his build and it appears too work very well. Or does it really require a double butterfly cap and a center vane earth. Looking to feed an antenna for 10 mt band as i have heard conditions are picking up. I haver never built nor used one before so should be an interesting experiment with different feeders and aerial combinations. There are no toroids nor coax involved in feeding and z matching the aerial, that was one of my caveats. Trying to rule out coax, PL259 connectors and toroids !. Any suggestions / ideas welcome |
26th Feb 2023, 7:06 pm | #2 |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,675
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Link Coupled ATU
I'm sure I saw a post about an hour ago with a similar title to this one
Was it in a different part of the forum? Anyway, it addressed the same dilemma that I had when I built this experimental ATU i.e. the difficulty in obtaining a differential "butterfly" VC
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26th Feb 2023, 7:24 pm | #3 |
Heptode
Join Date: May 2015
Location: Chatham, Kent, UK.
Posts: 947
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Re: Link Coupled ATU
Hi link to other post https://vintage-radio.net/forum/showthread.php?t=198628
mick |
26th Feb 2023, 7:28 pm | #4 |
Heptode
Join Date: May 2015
Location: Chatham, Kent, UK.
Posts: 947
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Re: Link Coupled ATU
Hi i built my own from parts https://www.etsy.com/uk/listing/8888...MaAnvhEALw_wcB just found the link Mick
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26th Feb 2023, 7:31 pm | #5 |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,675
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Re: Link Coupled ATU
Thanks Mick, I'll pull the emergency call cord, and ask the mods to merge the threads where they deem appropriate.
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26th Feb 2023, 7:49 pm | #6 | |
Octode
Join Date: Nov 2010
Location: Ross-on-Wye, Herefordshire, UK.
Posts: 1,648
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Re: Link Coupled ATU
Quote:
The purpose of the variable capacitors - as I understand it - is to alter the resonant frequency of the tuned circuit. That requires a standard variable ganged capacitor, where each section has the same capacitance value at each point in the rotation. |
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26th Feb 2023, 8:04 pm | #7 | |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,675
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Re: Link Coupled ATU
Quote:
On the other hand a normal VC is asymmetric, with one side connected to its frame and the control spindle. This could be isolated from ground but seems less than ideal in the circuit I posted. Is there a different VC that is ideally suited?
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26th Feb 2023, 8:20 pm | #8 | |
Octode
Join Date: Nov 2010
Location: Ross-on-Wye, Herefordshire, UK.
Posts: 1,648
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Re: Link Coupled ATU
Quote:
Sorry - I don't really understand what the problem is here. In the original circuit, we have the centre point of the two capacitors C1 grounded. So a totally standard variable capacitor, with the stator grounded, should meet the requirement. Not difficult to find at all! The rotors of these two capacitors go to the outer tapping points on L1, as indicated on the schematic. The only difficulty that you might have with the circuit is that of power levels, if you are using the ATU for transmitting. In which case you will have to watch the plate spacing on C1 is appropriate to whatever power you want to pass through the ATU. If its receive only, then any standard ganged variable capacitor should work just fine. |
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26th Feb 2023, 8:28 pm | #9 |
Octode
Join Date: Nov 2010
Location: Ross-on-Wye, Herefordshire, UK.
Posts: 1,648
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Re: Link coupled Z match
The old KW E-Z match type circuit should meet your requirements. That's described on various websites, but here's a typical one: https://vk6ysf.com/kw_ezee_match.htm
I don't think it requires any "exotic" variable capacitors at all. The ones pictured appear to be pretty standard. |
26th Feb 2023, 8:35 pm | #10 |
Heptode
Join Date: Jul 2018
Location: Worthing, West Sussex, UK.
Posts: 983
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Re: Link Coupled ATU
You could use just one capacitor on the primary side of this (with no earth centre tap) as long as you realise both sides of the cap will be RF "Hot"
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"Behind every crowd, there's a silver Moonshine" |
26th Feb 2023, 9:04 pm | #11 |
Triode
Join Date: May 2021
Location: Near Hereford, Herefordshire, UK.
Posts: 31
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Re: Link coupled Z match
Have been using this design for many years. Much easier than the original Z match.
http://users.tpg.com.au/users/ldbutl...CoilZMatch.htm |
26th Feb 2023, 9:05 pm | #12 | |
Octode
Join Date: Nov 2010
Location: Ross-on-Wye, Herefordshire, UK.
Posts: 1,648
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Re: Link Coupled ATU
Quote:
Quite. I suspect the only reason for having a dual gang capacitor at all is to go for easy construction by allowing the centre point - the common stators - to be grounded. |
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27th Feb 2023, 10:31 am | #13 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
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Re: Link Coupled ATU
As well as maintaining symmetry for feeding balanced-lines, the dual-capacitor approach also has the benefit that since both halves are wired in series, the RF voltage appearing across each half is halved.
If using old broadcast-capacitors with a beefy transmitter, the voltage issue becomes significant under certain (mis)matched conditions!
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27th Feb 2023, 11:51 pm | #14 |
Nonode
Join Date: Jun 2007
Location: Coulsdon, London, UK.
Posts: 2,152
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Re: Link Coupled ATU
I thought that it was the spindle, chassis and rotors that were grounded in a 'standard' dual gang variable capacitor.
The insulated 'stators' are then connected to the inductors. |
28th Feb 2023, 3:26 pm | #15 | |
Heptode
Join Date: Jan 2003
Location: Tewkesbury, Gloucestershire, UK.
Posts: 690
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Re: Link Coupled ATU
Quote:
Quite right. I've been using this arrangement for years to match a doublet to any frequency and keep it balanced to cancel noise.
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28th Feb 2023, 6:36 pm | #16 | |
Octode
Join Date: Nov 2010
Location: Ross-on-Wye, Herefordshire, UK.
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Re: Link Coupled ATU
Quote:
Richard |
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