I agree on the F/B issue. I built a long boom 15m yagi years ago that
worked great. I pointed it to JA from Colorado and it was quiet off the
back so much so that stations would constantly move in on my frequency.
For working big pileups simplex the F/B helped wipe out some of the
qrm. For most of my operating, I prefer max gain out the front and I
will take whatever F/B as long as the pattern is decent.
Mike W0MU
On 2/25/2011 7:28 AM, Joe Subich, W4TV 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.
> 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
>>>
>>>
>>>
>>> _______________________________________________
>>>
>>>
>>>
>>> _______________________________________________
>>> TowerTalk mailing list
>>> TowerTalk@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/towertalk
>>>
>>
>>
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