My SWR's are basically flat on the lower end of the 2m scale, but there is a
significant jump starting at 146.000 thru 147.999. Starting at 147.000,
it's pushing the 3:1 threshold and going over the 3:1 threshold the higher
in the freq band I go.

I have a discone antenna and would like some suggestions as to tuning
methods. From what I know, if the SWR's are high on the 'top' end of the
range, the main vertical whip needs to be trimmed.

Does that sound right or is there something else I need to check on first?

Thanks.

On Thu, 1 Apr 2004 11:58:42 -0500, "Macman"
wrote:

My SWR's are basically flat on the lower end of the 2m scale, but there is a
significant jump starting at 146.000 thru 147.999. Starting at 147.000,
it's pushing the 3:1 threshold and going over the 3:1 threshold the higher
in the freq band I go.

I have a discone antenna and would like some suggestions as to tuning
methods. From what I know, if the SWR's are high on the 'top' end of the
range, the main vertical whip needs to be trimmed.

Does that sound right or is there something else I need to check on first?

Thanks.


Hi OM,

There is no "tuning" of Discones. They are what they are,
broadbanded. Their lower frequency of use is basically defined by the
length of the lower skirt elements (verging on quarterwave). The
higher frequency is more a function of the feedpoint gap between the
disc and the cone. If this is adjustable, you are in luck. If it is
not adjustable, something else is broke.

As you describe a vertical whip, that is NOT the usual part of a
Discone, but is a means to offer an even lower single band's coverage,
usually 6M. It's addition is not a bonus at higher frequencies (and
may actually make the antenna deaf). However, this has nothing to do
with SWR. If this is a 6M addition, and you have the option of
removing it entirely, try that.

73's
Richard Clark, KB7QHC

Thank you Richard. This my first discone I've had a chance to play with and
didn't realize that verticle 'whip' was 6m. The lower radiating elements
that make up the cone; two of them have telescoping elements inside of the
main element. Maybe some gentle adjustments there would improve the top end
of the 2m band.
Thanks for you input.

On Thu, 1 Apr 2004 17:05:05 -0500, "Macman"
wrote:

Thank you Richard. This my first discone I've had a chance to play with and
didn't realize that verticle 'whip' was 6m. The lower radiating elements
that make up the cone; two of them have telescoping elements inside of the
main element. Maybe some gentle adjustments there would improve the top end
of the 2m band.
Thanks for you input.

Hi OM,

That determination of 6M was by dint of simple guess work. The
dimensions compared to wave length (quarterwave) will bear out what
part is responsible for the lowest frequency. The inclusion of
telescoping elements further complicates the analysis. Perhaps if you
were to supply dimensions, then we could shake the characteristics
out.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote:
There is no "tuning" of Discones. They are what they are,
broadbanded. Their lower frequency of use is basically defined by the
length of the lower skirt elements (verging on quarterwave). The
higher frequency is more a function of the feedpoint gap between the
disc and the cone. If this is adjustable, you are in luck. If it is
not adjustable, something else is broke.

As you describe a vertical whip, that is NOT the usual part of a
Discone, but is a means to offer an even lower single band's coverage,
usually 6M. It's addition is not a bonus at higher frequencies (and
may actually make the antenna deaf). However, this has nothing to do
with SWR. If this is a 6M addition, and you have the option of
removing it entirely, try that.

73's
Richard Clark, KB7QHC

Hi Richard,

Just wanted to mention, there are several discones on the market assembled
with circular arrays of horizontal and 45-degree angle groundplanes plus a
trimmable vertical element which is the only radiating element of those
discones. The vertical radiating element comes from the factory cut to 2m
but can be shortened to suit. I have owned a few and they are anything but
deaf.

Best regards,

Jack Painter
Virginia Beach

Not too in the way of specs for it, that could be my problem.
But I did find this http://www.wep4hams.com/base.htm that shows the one I
have.
Mine is the Workman T734 model.

On Thu, 1 Apr 2004 20:36:00 -0500, "Macman"
wrote:

Not too in the way of specs for it, that could be my problem.
But I did find this http://www.wep4hams.com/base.htm that shows the one I
have.
Mine is the Workman T734 model.


Hi OM,

Well, it is a bit difficult to count the number of radial elements,
but it looks like between 6 and 8. Also, given that it operates from
25MHz (in an attempt to encompass the earth, sea, and sky) it must
ultimately disappoint you somewhere. That somewhere is that above 3
to 4 times the lowest frequency, those higher frequencies invest their
attention to sending/getting signals from overhead instead of out and
away towards the horizon. Also with fewer radial elements, there are
going to be gaps in SWR coverage (your reports confirm this).

Too often the Discone vendor is content to cite only the matching
characteristics and not mention that directionality explodes upward
like a wind swept umbrella. So, even if it did match to 2M, it would
tend to be deaf. Like I said, try to eliminate the top whip, and
retract the lower skirts lengths to roughly 1M length or less.

73's
Richard Clark, KB7QHC

On Thu, 1 Apr 2004 20:21:39 -0500, "Jack Painter"
wrote:
Hi Richard,

Just wanted to mention, there are several discones on the market assembled
with circular arrays of horizontal and 45-degree angle groundplanes plus a
trimmable vertical element which is the only radiating element of those
discones. The vertical radiating element comes from the factory cut to 2m
but can be shortened to suit. I have owned a few and they are anything but
deaf.

Best regards,

Jack Painter
Virginia Beach

Hi Jack,

It would be if it were designed to a lowest resonation (through
lengths involved) at 25MHz.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Thu, 1 Apr 2004 20:21:39 -0500, "Jack Painter"
wrote:
Hi Richard,

Just wanted to mention, there are several discones on the market
assembled
with circular arrays of horizontal and 45-degree angle groundplanes plus
a
trimmable vertical element which is the only radiating element of those
discones. The vertical radiating element comes from the factory cut to 2m
but can be shortened to suit. I have owned a few and they are anything
but
deaf.

Best regards,

Jack Painter
Virginia Beach

Hi Jack,

It would be if it were designed to a lowest resonation (through
lengths involved) at 25MHz.

73's
Richard Clark, KB7QHC

Richard,

That makes sense...and the reason the ones designed as "scanner" antennas
are usually much shorter radials too, about 30" I think.. Though they
advertise 25-1300 mhz, I only used them for the 118-139 and 225-400 mhz
aircraft bands and 156 mhz marine band (where it was a poor performer in rx
and tx). The newer concept of discone called the "Scantenna" although for Rx
only, is a vastly superior performer than the standard discone design in the
bands I mentioned.

I currently use a J-Pole for marine band and have good 2-way between CG
Groups and aircraft over 100 miles distant. Accordingly, a J-pole woould
seem to be a natural for 2m work since mine is so close to that at 156.8
mhz, and it outperforms fishing-pole makers that advertise upwards of 6dbi.

73's

Jack Painter
Virginia Beach, VA