[TowerTalk] book Tribander comparison test

[Joe Subich, W4TV]

> Yeah, but there's another variable besides forward gain, bandwidth
> and feedpoint impedance: front-to-back ratio. The 3-el and 4-el
> SteppIRs have only about 11 dB F/B on 10m, which is less than half
> the F/B of a 3-el or 4-el 10m monobander with optimized element
> spacing.

You are correct, the 11 dB F/B on 10 meters is because the reflector
to driven element spacing has begun to approach 1/4 wave.  That's one
reason for the optional fixed parasitic elements on six meters.

I'm not convinced that high F/B is particularly important.  Most
other antenna specifications give the maximum F/B (anywhere in the
band) and many have significant fall off at the band edges.  It is
well known among antenna builders and modelers that maximum F/B
and maximum gain do not coincide except for a very few "fortunate"
boom lengths.  10 meter F/B is still better than a log-periodic
or tribanders from some other manufacturers.

73,

    ... Joe, W4TV


On 2/25/2011 2:21 AM, Dick Green WC1M wrote:
> Yeah, but there's another variable besides forward gain, bandwidth and
> feedpoint impedance: front-to-back ratio. The 3-el and 4-el SteppIRs have
> only about 11 dB F/B on 10m, which is less than half the F/B of a 3-el or
> 4-el 10m monobander with optimized element spacing. I'm no antenna design
> expert, but I have to believe this is due to the fixed element spacing. In
> that sense, the SteppIR is more like a tribander than a monobander (c.f.,
> the Force12 C3E, which has similar poor F/B on 10m).
>
> Don't get me wrong -- I have a 3-stack of 4-el SteppIRs and love 'em! In
> many respects they're like monobanders, but not in all respects.
>
> 73, Dick WC1M
>
>
> -----Original Message-----
> From: Joe Subich, W4TV [mailto:lists at subich.com]
> Sent: Thursday, February 24, 2011 8:33 PM
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] book Tribander comparison test
>
>
>   >  It would be, if they had motors to vary the distance between the
>   >  elements
>
> Nonsense!  Some 30+ years ago W2PV showed that a monobander was a
> monobander no matter what the element spacing as long as the elements
> are properly tuned for their place in the array.  Gain is a product
> of boom length as long as there are "enough" elements for the length.
>
> Tapered spacing only effects the bandwidth and feed impedance of the
> antenna and with a SteppIR bandwidth has no meaning since the antenna
> is constantly retuned for the operating frequency.
>
> SteppIR is a tunable "monobander" with a fixed length boom - other
> than the optional fixed length elements for six meters, a SteppIR
> has no traps or parasitic elements whose sole purpose is to allow
> operation on more than one frequency at a time.
>
> 73,
>
>      ... Joe, W4TV
>
>
> On 2/24/2011 6:57 PM, Dick NY1E wrote:
>>    " As far as the SteppIR, it's a monobander for all  practical purposes."
>>
>> It would be, if they had motors to vary the distance between the
> elements... otherwise its a tribander (ok 5 bander) with a good swr!
>>
>> Dick NY1E
>> www.ny1e.com
>>
>>
>>
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