Just a reminder, although there is time left to make comments on the proposed
UHF rules if you haven’t made comments you should do so. Now is probably better
than later. It is all well and good to make comments about the rules here on
the reflector, but to have a real impact they should be sent to the committee
at < vhf-input@arrl.org > by June 15. If you haven’t made your comments yet,
here is my rumination on the proposed band factors.
There have been some questions here about whether or not the band factors
suggested for the new contest are reasonable. I have had the same doubts
myself. At first glance they seem high. So, I set about to see if there is a
quantitative way to determine what the best band factors are. The answer is
“sort of”.
It is straight forward to calculate the path loss on a troposcatter path, and
combined with an assumed station capability, one can calculate the distances at
which the SNR is equivalent for the same power and same physically sized
antenna (increasing capture area with frequency) and use that to normalize
distances on the varying bands to determine at least part of the band factor.
There can be variation in troposcatter path loss calculations, so don’t take
these as gospel. I used the SM6FHZ excel spreadsheet to calculate the expected
troposcatter distances over a smooth earth. The distances calculated do show a
reasonable and mostly correct dependence with frequency though. Here are
normalized factors to adjust for the varying distance capability on the bands
up through 10GHz:
Band (MHz) Normalized distance (dn) for 3dB SNR in 500Hz bandwidth
222 1
432 1.1
902 1.4
1296 1.9
2304 2.4
3456 2.5
5760 2.3
10368 3.1
Three dB SNR in a 500 Hz bandwidth is a copiable CW signal to most experienced
weak signal ops.
The way to interpret these factors is that, with similar equipment, one can
work 3.1 times as far on 222MHz than on 10GHz, so the band factor, based solely
on distance, should be the reciprocal of that. As the contest is distance
scored, these should be a significant component of any band factor.
I stopped at 10GHz as the water absorption grows above that and I don’t have a
good way to calculate that now. I feel pretty good about recommending band
factors based at least partially on these numbers.
One of the goals of the committee is to increase activity. Thus, I think it
makes sense to calculate at least a part of the band factor by the level of
activity on the various bands. This data is easy to obtain from the contest
results on the ARRL web site. I just divided the number of total entries, which
was 175 for the 2015 UHF contest, by the number of entries per band to get a
factor by which to multiply the distance to encourage activity in inverse
proportion to current activity on the given band:
Band (MHz) Normalized participation (pn)
222 1.3
432 1
902 2.1
1296 1.6
2304 4.7
3456 6.3
5760 10.9
10368 6.3
No big surprises here, except that 5760 has the lowest participation and hence
the largest factor, which may dismay some who would like a smoothly increasing
factor with frequency. I thought that the 222MHz factor would be higher, but it
turns out that there were 138 222MHz entries out of the out of 175 total.
Interestingly enough, not all of the entries included 432MHz as there were only
172, out of 175 total, 432MHz entries.
A third thing to consider is that it is harder to get on the higher bands than
it is the lower bands and that the band factor should include something to
compensate for this difficulty. It is hard to quantify difficulty, so I took
the capitalist way out and determined the cost of similarly capable stations on
each band, including equal capture area antennas, and normalized them to 432
MHz. The station had 60W out to a 17ft Yagi or equivalent, and was background
noise limited. ON 5GHz and 10GHz, I assumed a 60cm (24 inch) dish.
Here are those factors:
Band (MHz) Normalized cost to 432MHz (cn)
222 1
432 1
902 1.2
1296 1.1
2304 2
3456 2
5760 2.1
10368 6.1
So, you can see that there is a jump at 2304MHz, and one at 10GHz. The jump at
10GHz is due to the large cost of a 60W amplifier from Kuhne; $4500. Accepting
lower power would reduce the price and put the difficulty in line with the
other microwave bands, but would affect the distance factor. You pays your
money and you takes your choices.
Now, how best to combine these factors to compute an overall band factor?
Damned if I know.
Well, I do have some ideas. One usually does not want to normalize
normalization factors, that is, the various factors should be added in some
fashion rather than multiplied. Depending on one’s preferences, not all of the
factors are of equal importance. How best to weigh the factors? The distance
factor should be used as is and given highest priority. How best to weight the
other two? The participation and cost factors are somewhat dependent on each
other as the activity is driven somewhat by the cost of a system.
My first Band factor generated was simply adding the distance and participation
factors with equal weighting, ignoring the cost contribution as it is partially
included in the participation factor. That is shown in the second column. The
third column is a band factor calculated by using the distance normalization
weight of 1, participation weight of 1, and the cost weighting of 0.5. The
proposed Committee band factors are listed in the last column.
Band (MHz) Band Factor 1 Band Factor 2 KK6MC Band
Factor Committee Band Factor
(dn+pn) (dn+pn+1/2*cn) MCFactor
222 2.3 2.8 3
1
432 2.1 2.6 2
1
902 3.5 4.1 5
4
1296 3.5 4.1 4
4
2304 7.1 8.1 10
20
3456 8.8 9.8 10
20
5760 13.2 14.7 15
20
10368 9.4 12.5 15
20
The KK6MC Band Factor column? That is a Band Factor I generated after doing
these calculations, combined with what I feel the Band Factor should be,
influenced a bit by these numbers, all rounded to nice integer numbers that
look good in the rules. They are intuitive, part objective, part subjective,
and neatly rounded off to integers. Here is what I was thinking when I
generated these numbers: I think activity should be incentivized more on 222MHz
and 902 than either my computed numbers or the committee’s band factors
indicate, as 222MHz is underused but has great capability, and 902 is underused
but can be a more of a struggle than 1296. I also think the transition from the
lower bands to the microwave bands is too abrupt in the committee’s factors.
So, to answer the question raised in the first paragraph, the committee’s
numbers are fairly reasonable, but I think they have too much spread in them,
probably are a bit high for the low microwave bands, and have breaks in the
wrong place. I suspect that the committee can make a reasonable case for them.
They probably went through an exercise similar to what I did, only with
different emphasis, which results in different numbers. But they aren’t way out
of line.
These assume that the dominant propagation mode used by competitors will be
troposcatter; line-of-sight and EME will distort the Band Factors.
If anyone wants more details of what I did, I can provide that, but the details
will probably give the impression that the calculations have more validity they
really do. - Duffey KK6MC
--
KK6MC
James Duffey
Cedar Crest NM
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