Good points. I agree that the jury is out on F/B. It's a particularly mixed
bag for contesting.
If domestic contacts count, as they do in WPX for example, low F/B can
actually be something of an advantage. It can also be helpful for S&Ping
when the band is open in multiple directions. In fact, one has to be careful
when running with an antenna that has high F/B: if you don't turn the
antenna enough you can easily miss mults from other directions. This is one
reason why the 40-2CD and XM-240 designs have withstood the test of time.
That said, low F/B will pass more noise from adjacent domestic stations,
sometimes making it more difficult to run under crowded band conditions.
Being able to receive better is often much more important than gain in a
contest.
73, Dick WC1M
-----Original Message-----
From: Joe Subich, W4TV [mailto:lists@subich.com]
Sent: Friday, February 25, 2011 9:29 AM
To: Dick Green WC1M
Cc: towertalk@contesting.com
Subject: Re: [TowerTalk] book Tribander comparison test
> 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@subich.com]
> Sent: Thursday, February 24, 2011 8:33 PM
> To: towertalk@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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>
>
>
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