Rick,
Thanks for pointing out that, unlike the tri bander, the gain and pattern
are only being shown for the center frequency on the mono banders. We will
correct that to be consistent. The website just went live yesterday and
this morning it was found that the link to those plots was broken. It got
fixed in 10 minutes.
I just ran the numbers for the 15m antenna as an example and here are the
gain and front to back numbers every 50 khz across the band
free space gain (dBi) Front to Back
21.000 8.52 26.35
21.050 8.56 30.36
21.100 8.6 36.95
21.150 8.64 49.83
21.200 8.67 36.75
21.250 8.7 31.65
21.300 8.72 28.8
21.350 8.75 26.98
21.400 8.77 25.76
21.450 8.79 24.99
I believe the average is about 32 dB front to back - not bad for a 17 foot
boom, 23 pound antenna that has an SWR of no higher than 1.16 at the very
highest point in the band - 21.450.
Just for the fun of it I shortened and then lengthened each of the
parasitic elements by 1/2 inch total.
Here are the numbers for bottom, mid and high end of band with all the
parasitic elements 1/2 inch short of design:
21.000 8.49 24.08
21.200 8.65 46.86
21.450 8.78 25.59
Here are the numbers with all the parasitic elements 1/2 loonger than the
design:
21.000 8.58 24.08
21.200 8.71 31.5
21.450 8.79 25.7
It is difficult to guess or make an assumption as to how far off the person
who puts the antenna together will have the dimensions. We have to assume
the person can read the tape measure. Although I would not recommend
pacing off the lengths on a 15m Yagi like I would do for an 80m dipole, it
is clear that there is some tolerance where the gain numbers do not change
significantly. The largest, huge dip off the back may be increased or
decreased by 5 or 10 dB and move to another frequency but the front to rear
doesn't change much overall even with the dimensions off by 1/2 inch.
We are not trying to hide anything here. This is not my source of living.
What we are trying to do is offer some great antennas and products at
prices people can afford. Less QRM for me if they have a directive antenna
pointed off the side :-)
73...Stan, K5GO
www.cycle-24.com
On Thu, Mar 21, 2013 at 4:00 PM, Richard (Rick) Karlquist <
richard@karlquist.com> wrote:
> On 3/21/2013 5:45 AM, Stan Stockton wrote:
>
>> Steve,
>>
>> Yes. Take a look at the little mono banders we have on our website
>> www.cycle-24.com.
>>
>> On many Yagi antennas you will see one frequency where there is huge
>> front to back. With these designs we have listed huge front to back
>> extends across the entire band. The antennas are modeled using EZNEC Pro/4
>> (NEC4). Actual models built and installed show these results in the real
>> world as best we can test them.
>>
>
> OK, I looked at www.cycle-24.com
>
> For the tribander, pattern vs frequency is shown. Good.
>
> For the monobanders, only center frequency gain
> and pattern are shown. Bad (but par for the course).
>
> But even these are only "typical" or "modeled" numbers.
> (Ever notice how modeled antennas have zero mechanical
> tolerances?) Ideally, there should be a guaranteed (worst case)
> minimum gain number over the band taking into account
> tuning tolerances.
>
> Rick N6RK
>
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