Drax Felton wrote:
> >From what I've read in materials from the ARRL is that anything under a
> 2.0:1 SWR is great.
>
> However, anything under a 5.0:1 SWR is negligible loss at HF frequencies.
> Fighting it lower is a pursuit of diminishing returns.
>
>
OTOH with a solid state rig it's a good idea to get it below 2:1.
My 756 Pro will operate pretty much the entire 40 meter band with the
internal tuner. However the solid state amp (Tokyo Hy-Power HL-1.5Kfx)
shows a substantial power drop with 1.2:1 compared to 1:1. At 1:1 it
runs 1 KW out. At 1.2:1 it is down to a bit above 800 watts. At 1.3:1
the reflected power will start tripping the protective circuitry.
So where I don't need an external tuner on 40 barefoot I do with the
amp. With the internal tuner in the 756 ro off, I can still cover most
of the 40 meter band but the power drops off. On 75 I can cover about
100 KHz centered on the lowest SWR. which is about 1.2:1 at 3.75
> Feed your antennas with ladder line and a tuner or put the balun as close to
> the antenna as possible to reduce transmission line losses.
>
Good, low loss coax will work fine on antennas like these across the
entire 74 and 40 meter bands.
The problem arises from solid state rigs and no matching. On those the
power will usually be reduced due to the mismatch and fold back from the
SWR or reflected power.
> Resonance is overrated. You want your radio to run full power into what it
> sees as an SWR under 2.0:1.
>
Simple wire antennas do not really care if they are resonant or not.
They will radiate all the power that gets to them.
73
Roger (K8RI)
> On the other side of the tuner or balun it really doesn't matter if it's
> 8:1, 15:1 or whatever because the losses are RF radiation losses and not
> losses as heat in the coax.
>
> What you want to prevent is a high SWR (> 5:1) on coaxial cable. On ladder
> line it doesn't matter.
>
> ARRL members can read this article that debunks the myths of SWR and
> resonance:
> www.arrl.org/members-only/tis/info/pdf/Reflect.pdf
>
>
>
>
>
> ------------------------------
>
> Message: 4
> Date: Sun, 09 Nov 2008 10:07:53 -0500
> From: Blair S Balden <blair.balden@wmich.edu>
> Subject: [TowerTalk] wire antenna question
> To: "towertalk@contesting.com" <towertalk@contesting.com>
> Message-ID: <3af18bee3559.4916b679@wmich.edu>
> Content-Type: text/plain; charset=us-ascii
>
> Hello antenna gurus,
> I have a question regarding wire dipoles that's been bothering me. I'm sure
> someone on towertalk can help. Here it is:
>
> When I put up dipoles, whether they be "straight" or inverted V's, I've
> always started out with the wire a little longer than the formula length of
> 468/f. Then I've trimmed for as close to a 1:1 match as I can get to my
> 50-ohm coax, as indicated by my SWR meter. I can usually get a 1:1 SWR.
>
> These antennas usually work very well, but I realize that a resonant dipole
> will not have exactly 50 ohms resistance. So, I must be cutting these
> antenna somewhat off resonance. I also realize that a mismatch at the
> antenna (SWR of greater than 1) results in loss.
>
> What I'm not sure about is whether it would be better to get the antenna
> resonant at the desired frequency and accept the mismatch, or whether I
> should continue to go for the best SWR (minimizing losses due to the
> mismatch).
>
> BTW, my rig does not have an internal antenna tuner, and I am currently
> without an external tuner for it. So, I'm running it without a tuner (if
> this matters). Also, I have not been using any kind of matching device at
> the feedpoint, just direct connection from the coax connectors to the wires.
>
> If someone on here can give me some insight as to whether I should try to go
> for resonance instead of low SWR, please respond. I would truly appreciate
> any help with the question.
>
> 73,
> Blair NP2F
>
>
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