[SJDXA] 160 Vertical Advice

Tue Oct 13 00:40:33 EDT 2020

Hi Steve,

It's a nice looking SWR curve but it doesn't necessarily tell the whole
story for a vertical.  Things may change as you add more radials; hopefully
a lot more.  The good news is that the antenna is at least resonant inside
the 160m band.

Recently, an FRC member was asking about verticals and radials for a
long-term project he has.  Bruce, WA3RHW was asking about how many radials,
how long, and using various kinds of excess wire he has.  Drew, K3PA
responded with some info but I thought you might want to take particular
note of his last point which I've highlighted in yellow below.

This is counterintuitive and can make you think you are doing the wrong
thing as you add more radials and you see your SWR curve go up.  I believe
the reason the SWR increases is because radiation resistance increases also
as the losses decrease and that is a good thing for a vertical.

Depending on what portion of the 160m band you intend to use, you may want
to lower the resonant point.

All CW contacts on 160m are made below 1900 KHz with the majority being 1870
and lower.

Even in the SSB contests, the distribution still favors the lower portion of
the band.

On the other hand, if you have a group you like to talk with around the
middle of the band, then 1885 where you have it now will work fine.

Typically antennas are evaluated for their 2:1 SWR bandwidth.  I believe
this is because this is the point where most rigs will begin to limit the Tx
power (or even sooner).  This antenna looks like it has a 2:1 BW of about 43
KHz from 1865 to 1908.

If I were optimizing it for contest usage, I'd shoot for about 1830 to 1835
as the center point.  This would put your 2:1 BW from 1810 to about 1853.
DX can't operate lower than 1810 so I give little concern to the very bottom
of the band.

73 & GL,

Bob - KE2D

P.S.  I love getting plots like this from the Rig Expert analyzer and
software.

K3PA's email:

From: GoFRC at groups.io [mailto:GoFRC at groups.io] On Behalf Of Drew
Vonada-Smith K3PA
Sent: Wednesday, October 07, 2020 8:34 PM
To: GoFRC at groups.io
Subject: Re: [GoFRC] Radials

Hi Bruce,

1.  On ground radials are not tuned.  There is no advantage to shortening
them.  Max 'em all out.
2.  True, depends on the quality of your soil and lots of other things.
More is always better.  If you are staying on a budget, start with 20 or 30.
3.  Copper wire is best for low loss.  Use what you have. Telephone quad
should be fine.  The MIL field wire is OK if it is copper outside and not
just steel.  Just tie the strands together.  Fence wire is usually
galvanized steel or aluminum.  Galv steel is too lossy and alum corrodes
quickly in many soils.  I'd avoid the fence wire.

You are right that the insulation does not matter.  The gauge does, a
little.  I'd go for 18 or 16 AWG as a minimum.  Mechanical fragility is an
issue as well.

There are ways to determine lossiness of the final product to determine how
close to perfect your radials are.  With more info on what the vertical is,
I can give more detail.  You need an antenna analyzer to determine the value
of R when X=0..  It is VERY important to note...if SWR goes up as you add
radials THAT IS NOT A BAD THING.  It usually means losses are decreasing.

73,
Drew K3PA 

From: sjdxa-bounces at mailman.qth.net [mailto:sjdxa-bounces at mailman.qth.net]
On Behalf Of Steve Molo (KI4KWR)
Sent: Monday, October 12, 2020 9:41 PM
To: sjdxa at mailman.qth.net
Subject: [SJDXA] 160 Vertical Advice

All, hope somebody can give me some ideas..

Cushcraft MA160V middle of yard / 3 radials so far at 50ft each 120 degrees
separation. Will be adding more but does this look good? Moving the stinger
we get go anywhere and have 40khz 1:1 or close to that.

Steve

KI4KWR

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