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Author Topic: Best band for QSO at 400 miles and 800 miles?  (Read 3088 times)
KG5MG
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Posts: 4




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« on: April 03, 2013, 10:00:28 PM »

I've been asked to help setup an HF station at the VA hospital where I work as part of an emergency communications plan.  We would like to be able to communicate with the hospital where we would send patients for specialty care which is a little over 400 miles west of our location and also our regional office which is about 800 miles to the west.

I have been out of ham radio for 15 years and never did much HF work when I was active before.

What bands would be most appropriate for daytime and nighttime to attempt this.

Right now we have a donated Icom IC-718 running 100 watts into a vertical mounted atop a building at about 15 feel. We may be getting some new equipment in the near future.

Thanks for any help.

Hamp KG5MG
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W8JX
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« Reply #1 on: April 03, 2013, 10:08:43 PM »

20m  day and 40m day and night with exception of mid afternoon for 800 miles on 40.
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K7MH
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« Reply #2 on: April 03, 2013, 10:28:27 PM »

In general terms, 40 during the day and 75/80 in the evening from my experiences with HF mobile operating. But of course it is nothing you can necessarily count on. There are at least a few variables to account for and the time of year will have an effect too.
I think many in "emcomm" think that HF communications has some certainty to it and it just doesn't.
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W1JKA
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Posts: 1770




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« Reply #3 on: April 04, 2013, 03:08:25 AM »

  Depending on resources available you may want to consider a dedicated beam type antenna to the West at least for 20m.
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M6GOM
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Posts: 945




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« Reply #4 on: April 04, 2013, 03:26:09 AM »

I've been asked to help setup an HF station at the VA hospital where I work as part of an emergency communications plan.  We would like to be able to communicate with the hospital where we would send patients for specialty care which is a little over 400 miles west of our location and also our regional office which is about 800 miles to the west.



Lower HF bands, horiztontally polarised antennas and keep the antennas low - NVIS. 80m band will do that just fine during the night and 40m band during the day. You won't get a reliable mobile solution for vehicles though.
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WA3SKN
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« Reply #5 on: April 04, 2013, 03:34:58 AM »

Set up for 20 and 40 meters, but plan on a 1/4 wave (or lower) high horizontal antenna (dipole or loop) and ditch the low angle radiation vertical!  100 watts should be fine.
73s.

-Mike.
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W8JX
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« Reply #6 on: April 04, 2013, 08:25:32 AM »

I would stay away for 80 because while it is a great winter time band, during warmer months it can be very noisy at times with a lot of static crashes too.
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WB6BYU
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Posts: 13336




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« Reply #7 on: April 04, 2013, 09:31:46 AM »

No single band - or even two bands - will guarantee coverage over the long term.
Over the last few years we've had to drop down to 160m to cover paths out to
400 miles on many occasions.  It all depends on the conditions in the ionosphere,
and that changes throughout the day, year, and with the sunspot cycle:  current
conditions aren't the same as those 2 years ago, or 2 years from now.

So you really need an antenna system for the two paths over multiple bands.  For
a long term solution that probably means 160m / 80m / 40m and 20m at least.
(If you are providing a data link then 30m might be a useful option.)

One useful approach is to look at some of the propagation prediction tools to see
what they forecast for coverage.  I like the tools from the Australian Ionospheric
Prediction Service because you can run them online here:

http://www.ips.gov.au/HF_Systems/7/1

The "Combined HF Prediction Tool" gives you a number of options:  the "Local
Area Mobile Prediction" (LAMP) tool shows what bands you can use for
distances out to 1000km (600 miles), which is easier to read than the more
detailed GRAFEX tool for point-to-point circuits.  The latter shows which
paths may be open, and includes the "Optimum Working Frequency" (OWF)
value - the frequency that is most likely to give reliable coverage for the path -
for each hour of the day.  (Currently it varies from about 5.5. MHz to 12.1 MHz
for the specific 800 mile path that I tried.)  For the LAMP display it has a preset
option for the ham bands, and color-codes the display based on the best band
vs. distance for each hour.

These will give you a prediction for the current conditions - you can manually
enter values for other conditions to see how it would affect the frequencies
needed.


In terms of antenna design, the optimum vertical radiation angle for a 400 mile
path is about 40 to 50 degrees, while for an 800 mile path it is 20 - 30 degrees.
(Approximations from scaling off a chart - exact value depends on the height
of the ionosphere.)  That means the optimum height for horizontal antennas will
be about 3/8 to 1/2 wavelengths.  Lower heights will work:  at 1/4 wavelength
the signal at 20 degrees is only down 8dB or so.  Higher antennas may not work
as well:  at 3/4 wavelength there is a null at 45 degrees, and the null drops to
30 degrees at 1 wavelength over ground.  (If the antenna is on a large metal
roof the calculation gets more complicated.)

For these angles a vertical antenna isn't a bad choice, as long as it has an
adequate ground plane, otherwise a simple dipole may out perform it.

Since both other sites are to the West you could plan some sort of directional
antenna, at least on some bands, to optimize coverage in that direction.
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W8JX
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Posts: 6060




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« Reply #8 on: April 04, 2013, 09:59:08 AM »

Nothing works 100% of the time but you can over complicate it too. When you talk about 160 and 80 you are talking large antennas and 160 has very high noise in warmer month. Not really a option for a reliable backup. 80 could work fine during cooler months in evening but noisy in summer and very short range during day. 40m is a very reliable daytime band short of a occasional solar storm. 400 miles is easy during day and more at night. 20 will work good to 800 miles during day. Will they work 100% of time? No but if you cannot do it it on one of those two band odd are no other bands too. Keep it simple and learn those two bands and they will serve you well.
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WB6BYU
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Posts: 13336




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« Reply #9 on: April 04, 2013, 11:13:18 AM »

Quote from: W8JX

...400 miles is easy during day  and more at night...



(My bold.)

And that is the problem:  as the band opens for longer distances the skip
zone gets longer as well, and you lose the shorter distances.

A current forecast for a 400 mile path suggests that 40m is open during the
day from 1300Z to 0100Z, and you'll need to drop down to 80m at night
even though 40m is still open for longer distances.  And that was for the
Gulf Coast:  here in Oregon at about 45N latitude 40m is only open for that
distance from 1600Z to 0200Z, and even 80m drops out from 0800Z to
1300Z when the skip "goes long".   We're used to using 80m during the day
and 160m at night for distances out to 300 miles over the last several years
because those were the only bands that were open at those distances.

The first requirement is to choose a band where the ionosphere supports
propagation over the desired path.  Just because signals are booming
in from all over the country doesn't mean it will cover shorter paths - in fact,
that may be a sign that you need to drop to a lower band.  In this case, if
you can hear the station at 800 miles but neither of you can copy the one
in between, you need to use a lower band.

Just because antennas are larger for 80m and 160m, and the bands are sometimes
noisy, doesn't mean that you shouldn't use them when they are the only bands
that will support the required communications.
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W8JX
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Posts: 6060




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« Reply #10 on: April 04, 2013, 12:00:31 PM »

I have spent a LOT of time on 40m so I know the band well. I can work into Florida from Ohio till about 1400z. During peak of day I get out to 5 to 600 miles with 400 miles easy. Around 2200z band starts to slowly go long again and 800 miles is possible but even till 0200 to 0300z 400 to 800 miles is not that rare. About a hour before and after sunrise 40 is at its longest for "local" stateside contacts but that changes quickly after sunrise. No band is perfect for the need here but 40 comes closest with 20 as a daytime backup.
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N6SBN
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Posts: 158


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« Reply #11 on: April 04, 2013, 05:31:22 PM »

I met an old ham at the local radiofest, who went on for half an hour about the need for a NVIS antenna for shorter range emergency comms.  I find that my vertical  connects from California to Texas, Florida and Japan .   I don't hear anything in the Western states.  There are numerous NVIS antenna designs on the net.
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K4RVN
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Posts: 778




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« Reply #12 on: April 05, 2013, 07:08:15 AM »

I agree with JX. If I had to suggest one band as the most reliable day and night for 400 to 800 miles, I would say 40 meters. That is based on several cycles , over 50 years experience in K4 land, and certainly not scientific propagation forecasts or real time data. 20 meters is good also in daylight.


Frank
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AA4PB
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Posts: 12893




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« Reply #13 on: April 05, 2013, 07:51:08 AM »

One nice thing about ham radio is that even if you can't work your station directly at times, you can always find someone to provide a relay for your really important traffic. Part of the plan should be that if you can't make contact on the prescribed frequency then you go to one of the established traffic nets where you can get some assistance.
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