[TowerTalk] Please Help Me Decide on a Tribander or Monobanders

[Richard Thorne]

I sure like my C31XR at 79' with a Delta 240 mounted 10' above it. I 
plan on changing out the 240 with a Delta 230/240  and lower it to about 
7' above the C31xr then add a WARC 2/2 at the 10' level.  That will give 
me a rotatable 10 through 40 solution.

I also have a C3 tribander (going on 17 years old) mounted on a 
rotatable swinging side gate at 40'.

I really like the F12 antennas, instant band change and made in America.

Rich - N5ZC


On 4/18/2013 4:06 PM, Wayne Willenberg wrote:
> My 86 or 89 foot crank-up tower project seems to be progressing through my
> County review boards.  So now I am getting really excited for my first
> tower.
>
> I am now in ham nirvana because I have to start making up my mind on which
> antenna(s) to put on the 15’ mast.  Here is my first dilemma.  Should I put
> up a tribander (10, 15 and 20M) or 3 monobanders.  My intuition said there
> was no way a tribander with the same 20M boom length could beat 3
> monobanders having a 20M antenna with the same boom length.
>
> So, just as an exercise, I looked at Force 12 antennas.  (I am not
> endorsing Force 12 antennas, although they do seem to have a good
> reputation.  I am also aware that the performance specs of antenna
> manufacturers need to be taken with a grain of salt –this is not meant to
> be a criticism of Force 12.)
>
> I started with the Force 12 model C-31XR tribander.  It has 14 elements on
> a boom length of 31’, a wind load of 10.7 sqft and published figures of:
>
> 20M gain: 14.0dBi, a F/B of 20dB,
>
> 15M gain: 14.3dBi, a F/B of 22dB, and
>
> 10M gain: 15.6dBi, a F/B of 21dB.  Published price: $2,970
>
> Then, I looked for monobanders from Force 12 that had a boom length for the
> 20M monobander close to the C-31XR and a gain in the vicinity of the of the
> tribander for each of the 3 bands.  Here is what I found:
>
> EF-420 (20M with 4 elements) has a boom length of 30’, a gain of 14.5Dbi,
> a  F/B of 22dB, a wind load of 5.5 sqft, and a cost of $1,300.
>
> EF-415 (15M with 4 elements) has a boom length of 20’, a gain of 14.6Dbi, a
> F/B of 22dB, a wind load of 2.8 sqft, and a cost of $869.
>
> EF-510 (10M with 5 elements) has a boom length of 18’, a gain of 15.1dBi, a
> F/B of 23, a wind load of 2.5 sqft, and a cost of $799.
>
> The total wind load of the 3 monobanders is 10.8 sqft and a total cost of
> $2,968.
>
> So, at first glance, the price and wind load of the tribander is
> practically the same as the sum of the 3 monobanders.  There is no more
> than an additional 0.5dB of gain (and 0.5 dB loss of gain on 10M) with
> monobanders;  a gain of 2dB F/B (and 2dB more F/B on 10M) for monobanders.
>
> However, I am aware that there will be a degradation of the performance of
> at least the middle monobander if I put 3 of them, in a Christmas tree
> fashion, on a 15’ mast.  I haven’t been able to find a good discussion of
> the amount of degradation—even the 22nd Edition of the Antenna Book has
> only a few words to say about this.  Please direct me to a discussion of
> this topic if you know one.  I may have to model these antennas on EZNEC to
> see the impact of 3 antennas confined to a 15 foot mast.
>
> On the other hand, there has to be a compromise when 3 antennas are mounted
> on a single boom.
>
> I would really appreciate your help in finding all of the specs I should be
> looking at in making this decision.  Any other comments that would push me
> one way or the other would also be appreciated.
>
> Please help me with my first tower!
>
> 73, Wayne KK6BT
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