Steve,
In your unlikely example it would be 15 dB. I think it would not be possible to
design an antenna such that the F/R changed by 10 dB in one KHz on the HF bands.
I certainly would not want to see one manufacturer say his antenna had 25 dB of
front to rear and then find out after buying it that it had 25 dB at 14.350 and
had a linear drop (approx .03 dB per KHz) in F/R as you went down to 14 dB at
14.000 and see another manufacturer's antenna passed up when his quoted number
for F/R was pretty consistent at around 20 dB across the band.
The data is not on line now but, for example, 2X Arrays had published gain,
F/R, F/B, R, X and SWR numbers every two KHz across the entire band for all
three bands on tribanders. This provided a lot of information in order for
people to make an informed decision. As I recall the F/R on a Tribander was
over 20 dB at every frequency on every band and varied not more than about a dB
at any frequency on any band. To me that is a whole lot better than the
previous example of one that went from 25 dB at a frequency I would likely
never operate and not be a lot better than a small two element antenna where I
did operate.
The main point is that some manufacturer's provide the highest gain figure that
occurs somewhere in the band and that frequency is usually not shown. Same for
F/B.
Because of the confusion and inconsistency in specs, there would be some who
would automatically think the pattern of an antenna with a specified F/B of 35
dB would trump an antenna where the specified minimum F/R at every frequency
was 20dB. I would choose the later with no other information provided.
73...Stan, K5GO
Sent from my iPad
> On Dec 11, 2014, at 5:43 AM, Steve Hunt <steve@karinya.net> wrote:
>
> Stan,
>
> I agree with what you say, but I'm challenging your idea of quoting an
> average. Let's say the F/R at 175 of the frequencies is 10db, and for the
> other 175 frequencies it is 20dB - what are you going to quote for the
> average F/R?
>
> Steve G3TXQ
>
>
>
>> On 11/12/2014 11:35, Stan Stockton wrote:
>> I'm talking about 350 numbers averaged, for example covering the 20 meter
>> band - not averaging two numbers like 10 and 20 dB and I'm suggesting that
>> because an antenna can have in excess of 60 dB of front to back at a few
>> frequencies that the F/R number is more important. Unless you are a
>> direction finding person or trying to null some particular source of QRM,
>> front to rear is a better number to look at. The thing to avoid is for one
>> manufacturer to claim 35 dB of F/B when in reality that occurs at 14.287 and
>> there is no place in the band where Front to Rear is even 20 dB while
>> another antenna is overlooked because it is shown to have 18-20 dB of F/R
>> across the band.
>>
>> Stan
>>
>> Sent from my iPad
>>
>>> On Dec 11, 2014, at 4:52 AM, Steve Hunt <steve@karinya.net> wrote:
>>>
>>> I agree that Free Space figures are probably the least ambiguous; but I'm
>>> not convinced that "averages" are very helpful!
>>>
>>> What do we mean by "average"? What's the average of two F/B ratios, one of
>>> 10dB and one of 20dB?
>>>
>>> [The average of 10dBW and 20dBW is 17.4dBW]
>>>
>>> A "not worse than" figure across the bandwidth may be more meaningful.
>>>
>>> Steve G3TXQ
>>>
>>>
>>>> On 11/12/2014 10:30, Stan Stockton wrote:
>>>> If every antenna were compared to every other antenna in terms of free
>>>> space gain and all in the same unit of measure (say dBI) and if the
>>>> numbers for gain F/B, F/R, etc were shown as average across the band then
>>>> there are no additional questions to ask to determine which antenna is
>>>> better or best.
>>> _______________________________________________
>>>
>>>
>>>
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>
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