Pls comment on this dipole
 

I have a span of approx 32 ft. to use for a horizontal dipole. It will
be about 40 ft high.

I want to use 2 parallel wires to cover 40M, 20M, and 15M. Ladder line
is not feasible here, so I need to tune the antenna for min SWR to
minimize coax feedline losses.

I would use 1 of the wires for 20M as a 1/2 wave dipole; and use the
other for 40/15.

The 40/15 will have off center loading coils at approx 11' on each
side (so it will be a 1/2 wave dipole for 15M), followed by more wire
to use the span. The coils would be designed to tune the whole span
for 40M, using either the Hamcalc program or one of the G4FGQ
programs.

Is the combined 40/15 element a reasonable idea? Or should I use
seperate wires for 40 & 15M?

I expect the interaction with the 20M wire will require several
pruning iterations.

Thanks in advance for any helpful comments.

73
Steve
K8SDK

Steve wrote:
Is the combined 40/15 element a reasonable idea? Or should I use
seperate wires for 40 & 15M?

66 ft dipoles work on 15m because they are 3/2WL long. Not just any
40m dipole with loading coils will work on 15m. Better use a separate
wire for 15m or turn the loading coil into an LC trap.
--
73, Cecil http://www.qsl.net/w5dxp



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"Steve" wrote in message
om...
I have a span of approx 32 ft. to use for a horizontal dipole. It will
be about 40 ft high.

I want to use 2 parallel wires to cover 40M, 20M, and 15M. Ladder line
is not feasible here, so I need to tune the antenna for min SWR to
minimize coax feedline losses.

I have had good results with one 40 meter dipole (a little coil loading to
shorten it shouldn't hurt), a 20 meter dipole suspended (by nylon string)
below it (about 3 ft below the 40m wire at the 20m wire ends) and a 15 meter
dipole suspended below the 20 meter dipole. All three dipoles were
connected in parallel at the center, and fed by 75-ohm (RG-59 or cable
coax). Never found a satisfactory length that would work well on 40 and 15
using one wire, so the extra 15m dipole solved the problem. Did not find
much, if any detuning caused by the extra dipoles, although the antenna
starts to look like a spider's web.

I also found no need for a balun when my coax came straight down to ground
level and then was run into the basement. The way to test to see if a balun
is needed is to check the resonant points on the three bands without a
balun, then put a balun in and retest. If the resonant points don't
noticeably increase in frequency when you insert the balun, then the balun
isn't needed. (i.e. the coax isn't radiating as if it's part of the antenna)
Fifty ohm coax (RG 58) will work also, but the SWR at resonance will be
somewhat higher - especially on 15m and 20m because of the height above the
ground. (75 ohm coax matches best when the dipole is higher than a half
wavelength over the ground.)

Good luck & 73, Andy K4YKZ

If you add a little series inductance at the feedpoint of the 40 meter
dipole, it'll load fine as a 3/2 wave on 15 meters. You can convert the
cloverleaf pattern on 15 to a bidirectional pattern with some gain,
without much effect on 40, by moving the wires together horizontally,
each by 30 degrees, for a 120 degree included angle -- if you have room,
and if you'll settle for essentially two-direction operation on 15.

But whether you use that scheme or not, a combined 40/15 meter dipole
and separate dipole for 20 should work well. I wouldn't put them in
parallel, but would hang the 20 meter antenna under the 40/15 as an
inverted vee, or separate them horizontally. That will make the
arrangement less critical to tune, and improve the bandwidth of at least
the 20 meter antenna.

Roy Lewallen, W7EL

Steve wrote:
I have a span of approx 32 ft. to use for a horizontal dipole. It will
be about 40 ft high.

I want to use 2 parallel wires to cover 40M, 20M, and 15M. Ladder line
is not feasible here, so I need to tune the antenna for min SWR to
minimize coax feedline losses.

I would use 1 of the wires for 20M as a 1/2 wave dipole; and use the
other for 40/15.

The 40/15 will have off center loading coils at approx 11' on each
side (so it will be a 1/2 wave dipole for 15M), followed by more wire
to use the span. The coils would be designed to tune the whole span
for 40M, using either the Hamcalc program or one of the G4FGQ
programs.

Is the combined 40/15 element a reasonable idea? Or should I use
seperate wires for 40 & 15M?

I expect the interaction with the 20M wire will require several
pruning iterations.

Thanks in advance for any helpful comments.

73
Steve
K8SDK

"Steve" wrote in message
om...
I have a span of approx 32 ft. to use for a horizontal dipole. It will
be about 40 ft high.

I want to use 2 parallel wires to cover 40M, 20M, and 15M. Ladder line
is not feasible here, so I need to tune the antenna for min SWR to
minimize coax feedline losses.

remember, "too low an swr can kill you!". unless you are going hundreds of
feet and using rg-58 for coax the losses on hf are small.

Steve,

I had a situation something like that. Wanted 40, 17 and 12 meters, but the
trees were too close for 40. I supported the whole thing from the 17m
dipole, hung the 12 underneath it (ends were separated by about 5 feet), and
strung a full length 40m inverted V from the same feedpoint, but about 30
degrees out of plane with fairly low end supports.

In tuning up, go from the lowest to the highest frequency, or it might not
converge.

A 40m inverted V makes a lousy 15m antenna. I would use a separate dipole
for 15. Run EZNEC first to get in the ballpark.

Tam/WB2TT
"Steve" wrote in message
om...
I have a span of approx 32 ft. to use for a horizontal dipole. It will
be about 40 ft high.

I want to use 2 parallel wires to cover 40M, 20M, and 15M. Ladder line
is not feasible here, so I need to tune the antenna for min SWR to
minimize coax feedline losses.

I would use 1 of the wires for 20M as a 1/2 wave dipole; and use the
other for 40/15.

The 40/15 will have off center loading coils at approx 11' on each
side (so it will be a 1/2 wave dipole for 15M), followed by more wire
to use the span. The coils would be designed to tune the whole span
for 40M, using either the Hamcalc program or one of the G4FGQ
programs.

Is the combined 40/15 element a reasonable idea? Or should I use
seperate wires for 40 & 15M?

I expect the interaction with the 20M wire will require several
pruning iterations.

Thanks in advance for any helpful comments.

73
Steve
K8SDK

Thanks to all.

I'll go with the seperate 15M wire, & let you know how it turns out.

73
Steve

K8SDK