Elecraft

[Sorta OT]: Does terrain affect HF radiation patterns?

Classic

List

Threaded

4 messages Options

Al Gulseth-2

[Sorta OT]: Does terrain affect HF radiation patterns?

Greetings all,

I've been following some of the antenna-related discussions here recently, and
I've decided to see what the "gurus" here have to say about a question I have
related to my QTH. As my post title indicates, what (if any) effect does
nearby terrain have on HF radiation patterns? Is it along the lines of VHF?

Without going into too much detail, my QTH is partway up what amounts to a
long broad slope to the north. "Just for grins" I plugged my QTH coordinates
and an arbitrary antenna at 50 feet AGL into the FCC's Height Above Average
Terrain calculator. Here are the results, in meters of course, which shows
what the surrounding terrain is like; the results seem realistic from what I
know of the local area. I would also note that the area less than two miles
away, which is not used in these calculations, would nevertheless correspond
fairly closely slope-wise in my estimation. I'm aware that this calculation
is intended for FM/TV broadcast: my question is whether it could be of use
for hams on HF:

Antenna Radiation Center Heights Above Individual Radials:

0.0° -107.3 meters
45.0° -37.4 meters
90.0° 39.6 meters
135.0° 100.3 meters
180.0° 92.9 meters
225.0° 86.6 meters
270.0° -1.6 meters
315.0° -40.0 meters

Now, my observations: I've been using an inexpensive SW portable with its
built-in whip to monitor some of the International Beacon Project and 10M
beacon frequencies while I'm around the house. By using the portable, in my
estimation I achieve two things: 1) it should "hear" a mostly omnidirectional
pattern and 2) beacons heard under this circumstance should indicate the band
would be usable to the area in the beacon's vicinity.

That being said, I have found that other than 4U4UN, I'm most consistently
hearing South American beacons, and at least some of them can usually be
heard if I'm hearing anything at all. So, is the terrain around me affecting
this, or if not, what might be happening?

TNX/73, Al
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

k6dgw

Re: [Sorta OT]: Does terrain affect HF radiation patterns?

Try HFTA, by Dean N6BV, who edited the ARRL Antenna Book for many years.
It's on the CD that comes with the current edition. It will surprise you.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2014 Cal QSO Party 4-5 Oct 2014
- www.cqp.org

On 9/15/2014 6:54 PM, Al Gulseth wrote:

> Greetings all,
>
> I've been following some of the antenna-related discussions here recently, and
> I've decided to see what the "gurus" here have to say about a question I have
> related to my QTH. As my post title indicates, what (if any) effect does
> nearby terrain have on HF radiation patterns? Is it along the lines of VHF?
>
> Without going into too much detail, my QTH is partway up what amounts to a
> long broad slope to the north. "Just for grins" I plugged my QTH coordinates
> and an arbitrary antenna at 50 feet AGL into the FCC's Height Above Average
> Terrain calculator. Here are the results, in meters of course, which shows
> what the surrounding terrain is like; the results seem realistic from what I
> know of the local area. I would also note that the area less than two miles
> away, which is not used in these calculations, would nevertheless correspond
> fairly closely slope-wise in my estimation. I'm aware that this calculation
> is intended for FM/TV broadcast: my question is whether it could be of use
> for hams on HF:
>
> Antenna Radiation Center Heights Above Individual Radials:
>
> 0.0° -107.3 meters
> 45.0° -37.4 meters
> 90.0° 39.6 meters
> 135.0° 100.3 meters
> 180.0° 92.9 meters
> 225.0° 86.6 meters
> 270.0° -1.6 meters
> 315.0° -40.0 meters
>
> Now, my observations: I've been using an inexpensive SW portable with its
>
> built-in whip to monitor some of the International Beacon Project and 10M
>
> beacon frequencies while I'm around the house. By using the portable, in my
> estimation I achieve two things: 1) it should "hear" a mostly omnidirectional
> pattern and 2) beacons heard under this circumstance should indicate the band
> would be usable to the area in the beacon's vicinity.
>
> That being said, I have found that other than 4U4UN, I'm most consistently
> hearing South American beacons, and at least some of them can usually be
> heard if I'm hearing anything at all. So, is the terrain around me affecting
> this, or if not, what might be happening?
>
> TNX/73, Al
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>
>
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 2014.0.4765 / Virus Database: 4015/8219 - Release Date: 09/15/14
>
>
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

Jim Brown-10

Re: [Sorta OT]: Does terrain affect HF radiation patterns?

In reply to this post by Al Gulseth-2

On Mon,9/15/2014 6:54 PM, Al Gulseth wrote:
> Greetings all,
>
> I've been following some of the antenna-related discussions here recently, and
> I've decided to see what the "gurus" here have to say about a question I have
> related to my QTH. As my post title indicates, what (if any) effect does
> nearby terrain have on HF radiation patterns?

The short answer is that terrain has a MAJOR effect on the vertical
patterns of antennas, and that effect can be predicted by modeling. The
effects are very different at HF as compared to VHF.

RUN, do not walk, to the closest place you can buy the ARRL Antenna
Book. It includes both a good discussion and a very useful piece of
software called HFTA (high frequency terrain analysis) by N6BV. I and
many of my contesting cohorts have used it extensively, and are true
believers.

This is one time you do NOT want a used copy of the book, because the
software is on a CD that will likely not be in a used copy.

You can probably find a lot of stuff on the web by searching on HFTA.
The author, N6BV, did a nice webinar a couple of years ago. PVRC, a big
contesting club based around MD/VA/EPA organized it, and it was on their
website.

73, Jim K9YC
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

Al Gulseth-2

Follow-up: [Sorta OT]: Does terrain affect HF radiation patterns?

In reply to this post by Al Gulseth-2

First, TNX for all the replies. You've given me a lot of information to wade
through. In doing a quick browse about HFTA on the web I found a couple of
presentations, which while being "apples and oranges" to my situation,
nevertheless exhibited some of the same characteristics. It was really
educational to see their graphs of what terrain can do to a signal's take-off
angle and how the height of the antenna interacts with the terrain.

That being said, I'm wondering if this explains another phenomena I've
observed. Another "beacon" system exists in the form of W1AW in that it gives
a picture of closer in/domestic propagation on the various bands. In my
experience their signal on 20M is surprisingly weak here most of the time,
while 17M frequently shows full strength on the signal indicator during the
periods when I'd expect that band to be open. I've also seen times when 17
and 40M were both fairly strong, and it would seem logical that 20 should
also be in the "sweet spot" at that moment, but it isn't. Is this possibly
due to the terrain/antenna combination either on my end or W1AW's?

Again, TNX for the very informative comments. 73, Al

On Mon September 15 2014 8:54:38 pm Al Gulseth wrote:

> Greetings all,
>
> I've been following some of the antenna-related discussions here recently,
> and I've decided to see what the "gurus" here have to say about a question
> I have related to my QTH. As my post title indicates, what (if any) effect
> does nearby terrain have on HF radiation patterns? Is it along the lines of
> VHF?
>
> Without going into too much detail, my QTH is partway up what amounts to a
> long broad slope to the north. "Just for grins" I plugged my QTH
> coordinates and an arbitrary antenna at 50 feet AGL into the FCC's Height
> Above Average Terrain calculator. Here are the results, in meters of
> course, which shows what the surrounding terrain is like; the results seem
> realistic from what I know of the local area. I would also note that the
> area less than two miles away, which is not used in these calculations,
> would nevertheless correspond fairly closely slope-wise in my estimation.
> I'm aware that this calculation is intended for FM/TV broadcast: my
> question is whether it could be of use for hams on HF:
>
> Antenna Radiation Center Heights Above Individual Radials:
>
> 0.0° -107.3 meters
> 45.0° -37.4 meters
> 90.0° 39.6 meters
> 135.0° 100.3 meters
> 180.0° 92.9 meters
> 225.0° 86.6 meters
> 270.0° -1.6 meters
> 315.0° -40.0 meters
>
> Now, my observations: I've been using an inexpensive SW portable with its
> built-in whip to monitor some of the International Beacon Project and 10M
> beacon frequencies while I'm around the house. By using the portable, in my
> estimation I achieve two things: 1) it should "hear" a mostly
> omnidirectional pattern and 2) beacons heard under this circumstance should
> indicate the band would be usable to the area in the beacon's vicinity.
>
> That being said, I have found that other than 4U4UN, I'm most consistently
> hearing South American beacons, and at least some of them can usually be
> heard if I'm hearing anything at all. So, is the terrain around me
> affecting this, or if not, what might be happening?
>
> TNX/73, Al
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]