W3EA is on point and very correct.
I remember reading K1EA's advice about odd quarter wavelengths of cable in a
YCCC Butt articles in the late 70s and early 80s.
I have used Ken's advice ever since. Stacking 2, 3 or 4 Yagi's with great
results since 1981. The models back up his recommendation - good engineering
practice.
Using a Monostacker relay switch design (as published in the NCJ by K3LR and
K3LC many years ago) at K3LR on all bands using coax quarter wavelength
sections to provide the matching transformers for 2, 3 or 4 Yagi's being fed
in a stack (no ferrite transformers). These are single band stacking systems
using good quality open frame relays (hot switching traps are EASY to
achieve inside the shack - no failures here). There are 10 combinations of
stacking or individual Yagi's (4 high) - with perfect matching (OWA feeds)
no matter what combination is selected - the exact same length of coax from
loads to the amplifiers. That means the amplifier never sees an odd multiple
change - which would rotate on the Smith chart and cause retuning of the
amplifier.
73,
Tim K3LR
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Wayne
Kline
Sent: Friday, May 04, 2018 6:16 PM
To: Wes Stewart; Richard (Rick) Karlquist; towertalk@contesting.com
Subject: Re: [TowerTalk] Coax Lengths for Stacked Yagis
MY reason for using odd multiples of ¼ wave feed line. Was all my antennas
are either Beta match or direct feed OWA. Purely resistive loads not
capacitive as in a beta match.
Speaking to Ken K1EA many years ago.. and others. he was the one who
strengthened the notion . @ odd multiply 1/3 wave transmission line Voltage
in minimum and current is maximum.
Wayne W3EA
Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows
10
________________________________
From: TowerTalk <towertalk-bounces@contesting.com> on behalf of Wes Stewart
<wes_n7ws@triconet.org>
Sent: Friday, May 4, 2018 4:07:32 PM
To: Richard (Rick) Karlquist; towertalk@contesting.com
Subject: Re: [TowerTalk] Coax Lengths for Stacked Yagis
I probably should have been a little more specific; there are some special
case
exceptions.
Roy Lewallen says on page 6-15 in my 22nd Edition of the ARRL Antenna Book:
"The only cases in which the current (or voltage) delay is equal to the
electrical
length of the line are
1) When the line is flat; that is, terminated in a purely
resistive load equal to its characteristic impedance;
2) When the line length is an integral number of half
wavelengths;
3) When the line length is an odd number of quarter
wavelengths and the load is purely resistive; and
4) When other specific lengths are used for specific load
impedances."
Wes
On 5/3/2018 9:24 PM, Richard (Rick) Karlquist wrote:
> Isn't it true that for lines that have a length
> that is any multiple of a quarter wave,
> the phase shift when matched is the same as when mismatched?
>
> Otherwise, (1) is correct AFAIK.
>
> Rick N6RK
>
> On 5/3/2018 9:06 PM, Wes Stewart wrote:
>> Another point or two and then I'll shut up.
>>
>> 1) The expected phase shift in a line is only achieved when the line is
>> matched.
>>
>> On 5/3/2018 7:28 PM, Wes Stewart wrote:
>>> Quarter wavelength lines have the magical property that the output
current
>>> is equal to the input voltage divided by the line Zo. So with multiple
>>> inputs tied together, and obviously having the same voltage, the output
>>> currents will be equal.
>
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