There is no difference between a hairpin match and a beta match, its just 2
different names for the same thing.
My understanding of them is that it's a device for raising the feedpoint Z
of a yagi, typically 25-35 ohms, up to 50 ohms. But when you build one, you
can only adjust its length for one frequency band. I have never seen one
used on a tribander, only on monoband antennas.
Could this be another example of confusion on the part of the folks at MFJ?
Maybe they got tribanders mixed up with monobanders and just stuck a beta
match on the TH-3JR-S because they didn't know any better.
All of the trapped tribanders that I have worked with, and it's been quite
a few, were direct fed with no matching system. The losses in the traps
probably provide the extra Z to arrive at 50 ohms.
It might be worth just removing the beta match altogether and see what
happens.
K0SN
On Sun, May 18, 2025 at 10:33 AM Bill Cotter <n4lg@qx.net> wrote:
> Gary,
>
> Attached is the manual for the TH-3 MK3 that shows the (grounded)
> beta-match dimensions, and the coax choke. I think the hairpin may
> be the problem (inductor vs transmission line). I think I would
> construct the beta match as designed. It should be easy to make up
> from available materials. And, thoroughly inspecting the traps for
> electrical integrity and correct location is a must.
>
> 73 es GL Bill N4LG
>
>
> At 09:19 AM 5/18/2025, Gary Mayfield wrote:
> >Thanks Jim,
> >
> > We did test with the long coax on the ground, and your
> > point is well taken about the balun vs a choke. We will take a
> > fine tooth comb to our hairpin recreation. I suspect that may be
> > a contributing factor.
> >
> >73,
> >Joe n0sd
> >
> >-----Original Message-----
> >From: TowerTalk <towertalk-bounces@contesting.com> On Behalf Of
> >Jim Brown
> >Sent: Saturday, May 17, 2025 11:18 PM
> >To: towertalk@contesting.com
> >Subject: Re: [TowerTalk] HELP - Hy-Gain TH-3JRS
> >
> >On 5/17/2025 6:04 PM, Gary Mayfield wrote:
> > > We have also added a balun made from type 31 ferrite material.
> >
> >Hi Gary,
> >
> >Don't know anything about that antenna or have a solution for your
> >problem, BUT -- if that #31 is a lot of turns of transmission line
> >wound around a 2.4-in o.d. core, it is a Common Mode Choke, NOT a
> >"balun."
> >Antennas like yours are designed for specific matching networks or
> >feeding methods. A choke is used between the transmission line and
> >that matching system, whatever it is. These matching systems are
> >often called baluns.
> >
> >And with respect to your problem and on-the-ground testing -- did
> >you have a long length of coax on it when testing on the ground,
> >or just the analyzer connected with a few feet of coax? Their
> >matching networks often want to be driven by that coax.
> >
> >Also, study carefully as you can what the original matching system
> >was.
> >With gamma and hairpin matching, both the length and the diameter
> >of the
> >rod(s) matter.
> >
> >73, Jim K9YC
> >
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> >
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