Topband: Hairpin Matching Coil Questions

Wed Sep 18 15:18:17 EDT 2013

Sorry, I just looked at my own post and I see that the reflector or e-mail
changed my superscripts to lower case.

The formula is Q(squared) +1 or Q*2 +1

Sorry,
Charlie, K4OTV

-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Charlie
Cunningham
Sent: Wednesday, September 18, 2013 2:44 PM
To: 'Jim GM'; 'Tom W8JI'
Cc: 'topband'
Subject: Re: Topband: Hairpin Matching Coil Questions

Hello, Jim

You seem to be "lost"!

First of all, the "thing" that you originally called a "hairpin match" is
NOT a "shunt match".  The coil, or "hairpin" is in SERIES with the reactance
and radiation resistance and copper losses of the antenna!

For the "thing" to "work" the antenna must be shortened some from its
resonant length, so that its series reactance is capacitive.

The "formula" that you are looking for is Q2+1, that is the impedance
transformation formula for an L-network. In this case the L-network is
formed by the series capacitive reactance  of the antenna element and the
shunt inductance of  the coil or "hairpin".

If your antenna looks like 25 ohms resistive at resonance, then the required
loaded Q of the network = 1, so that 25 ohms( Q2+1) = 50 ohms.

>From that we could deduce that |jXL| = 25 and |jXc| = 25.

So, you could start your design by calculating L. I believe that you would
find that it's approx. 8.8 uH.

Then shorten the antenna to resonate with that.

BUT - why not just connect the coax directly to the end of the vertical???
If it looks like 27 ohms, as you say, then the excess loss in any
reasonable, finite length of RG-8 or RG-213 over the flat-loss in the same
length of line at 1.8 MHz is negligible.  Just match the feedling in the
shack!

Sorry, but for me to derive all of the above numbers and formulas from first
principles would require more derivation, more tutorial and more  time
typing mathematical formulas, and symbols and superscripts and subscripts
than I have time for at the moment.

73,
Charlie, K4OTV

-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Jim GM
Sent: Wednesday, September 18, 2013 1:05 PM
To: Tom W8JI
Cc: topband
Subject: Re: Topband: Hairpin Matching Coil Questions

The thing works, I mean the shunt match works.

what would be a good Q for just the coil?  300, 600, 900

Operating Q, what is the desired value?  Whats your formula for that?

Q of the operating antenna, cannot be expressed as band width equation I
see so many others use. there is another quick easy formula that, may be a
function or derivative that has some relationship, but not the number we
really want.  Not even sure if it would get every one in every situation in
the ball park.

On Tue, Sep 17, 2013 at 4:31 PM, Tom W8JI <w8ji at w8ji.com> wrote:

> Hi Jim,
>
> A gamma match is an arm extending out or up on the element from the
> "ground" point. It is named "gamma" because it looks like the capital
Greek
> letter called "gamma". See
http://en.wikipedia.org/wiki/**Gamma<http://en.wikipedia.org/wiki/Gamma>
>
> A beta match is called a beta because it extends equally on each side of
> the neutral point, roughly looking like the Greek letter beta on it's side
> http://en.wikipedia.org/wiki/**Beta <http://en.wikipedia.org/wiki/Beta>
>
> A hairpin match is a hairpin shaped "stub inductor", generally balanced,
> but it could be unbalanced.  It is called a hairpin because it looks like
a
> hairpin, just like a "bobby pin" spread out a little.
>
> A shunt matching component can be used, either an inductor or capacitor,
> but this is typically called shunt matching because it is a shunt
component
> across the feedpoint. It is not a hairpin unless it is in the form of a
> hairpin.
>
> Hairpins and shunt matching generally act like L networks, with the series
> reactance in the element (caused by adding or subtracting length to move
> the element away from resonance). Gamma and Beta matchs can do the same,
> use the adjustment in length away from resonance to act like a reactance,
> or the Gamma or Beta might contain a series internal component(s) so the
> element can be resonant.
>
> Q can mean many things. The style or construction of the component usually
> has little bearing on the operating Q of the system, unless you have a
> terrible matching system or component design.
>
> The Q people generally talk about in matching is almost always operating
> Q. Operating Q is generally the ratio of real parts of impedance to
> imaginary parts of impedance, or operating resistance compared to
component
> reactances in simple systems. For example a simple parallel tank circuit
> with a reactance of 500 ohms in each component shunted by 5000 ohms has an
> operating Q or loaded Q of ten. The component Q might be 300, or 3
zillion,
> and not affect operating Q significantly.
>
> The Q of components is entirely different than operating Q of a system,
> and is the ratio of reactance to resistance in a component.
>
> Q can also be used to describe bandwidth, but if the component or system
> is more complex than a single resonant L, R, and C the Q defined by
> bandwidth might not be related at all to system operating Q as defined by
> losses.
>
> When I think about all of that, and your desire for a certain coil
> conductor type for a Q of 80 for a hairpin (that doesn't use a coil by
> definition of being a hairpin), none of it makes much sense to me. The Q
of
> a very simple matching system would generally be discussed as a ratio of
> matching system reactance to resistance of the system at that matching
> point. The Q of a component in the matching system would generally be
> defined as the ratio of loss resistance to reactance of that component by
> itself.
>
> For example, a 200 ohm reactance capacitor of 0.05 ohms loss resistance in
> series with an antenna feedpoint of  50 j200 to cancel reactance and match
> the system would have a component Q of 4000 (200/.05) and an operating Q
of
> 3.996 (200/50.05). If I put in a capacitor with a reactance of 200 ohms
but
> a seres loss resistance of .5 ohms, capacitor Q would be 400. This would
> insigificantly change operating Q to 200/50.5 = 3.96.
>
> This all makes me think you have operating Q confused with component Q.
>
> Are you trying to solve some problem by reading stuff somewhere, and
> getting confused by it??? Maybe some misinformation or misunderstanding is
> making your project needlessly difficult for you to manage?
>
> 73,
> Tom
>
>
>
>
>
>
>
>
>  MFJ and Texas Instrument used this type of calculation for antenna Q.
>>
>> The other attachment is what some other people are using with their
>> inverted using the K2AV balun and a Gamma match on bands other than 160M.
>> So I thought why not use the same gamma setup on 160M and not the FCP. So
>> from what you had said best I DO NOT GO THAT ROUTE.
>>
>> My antenna system morfed into just using my gamma big coil on 160M.
>>
>>
>> On Sun, Sep 15, 2013 at 9:32 AM, Jim GM <jim.gmforum at gmail.com> wrote:
>>
>>  Has any one used the MFJ-907 and do what I am trying to do on 160M as a
>>> hairpin match?
>>>
>>>> From what I have been reading, Q needs to be high but not sure how high
>>>>>
>>>> and what range.  My 6 inch coil with remote tuner in line with the tap
>>> on
>>> 160m I am getting around a Q of 80. My 2 inch coil has a Q much lower
>>> than that I know cause the set up has a much larger band width on 160M.
>>>
>>> I have around 30 to 40mh of coil from the tap to ground with both coils.
>>> --
>>> Jim K9TF
>>>
>>>
>>
>>
>> --
>> Jim K9TF
>> _________________
>> Topband Reflector
>>
>>
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>

-- 
Jim K9TF
_________________
Topband Reflector

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Topband Reflector