Elevation and shortwave propogation

[dragon48]

I have great radios, but don't have any really good antennas, just some active antennas that do a reasonable job of picking up strong shortwave signals in NYC, but overall, my shortwave reception is bad. I was surprised that when I traveled 100 miles to a rural part of Eastern Long Island, the reception didn't improve.

I then realized that both locations are basically at sea level, maybe 30-50 feet higher and was wondering if this limits reception. I can travel the same 100 miles, but instead travel northwest, and land in a spot around 1,300 feet above sea level. Will this get me much better reception? If so, if I travel a little farther north, I can get up to a little more than 3,100 feet above sea level. Would this get me better reception that the spot 1,300 feet above sea level.

Thanks

 

[ka3jjz]

No it likely won't make any difference. You must consider 2 factors here - one is that the sun has been very uncooperative lately. HF Propagation heavily depends on solar activity and interaction with the ionosphere. This website is a good intro into this subject...

Propagation Primer - Flash Movie by AE4RV

(note: Turn your flash player on for this site)

Now as to height - your station height really isn't the limiting factor, it's how high your antennas are off the ground. Actives are less sensitive to this issue, but many antennas, such as dipoles, need to be a certain height off the ground to work properly.And as a general rule, indoor antennas can't match the performance of an outdoor antenna, out away from all the noise sources inside a typical home. But for many, this is not always practical or doable. If you are able to get your actives outdoors, likely as not things will improve, but it's nearly impossible to quantify by how much. The ionosphere is, to paraphrase, a fickle master.

Mike

 

[wyShack]

Propagation at MW and SW is mostly unaffected by elevation in that 'line of sight' is not near the factor it is at VHF and up. While it does have some effect on antenna performance (as noted above), most reception is not 'line of sight'.


It may help to remember that it is not just the signal strength, but the signal to noise ratio that helps reception. Almost any receiver is sensitive enough but in today's world, selectivity is often more important. One thing to try is tuning AM signals in USB or LSB- if your receiver adds extra filters for SSB you may be surprised. Also experiment with gain if you can -max sensitivity also means max noise and often you get a better (*sometimes much better) signal to noise ratio at lower gain settings. Part of the hobby of shortwave is experimenting (both with the radio and different antennas). Patience is often the only tool that works.

73 and good luck

 

[prcguy]

In the lower HF/SW range up to maybe 10MHz where most people have wire antennas maybe 10 to 20ft off the ground, the radiation pattern will be mostly straight up with diminished reception towards the horizon. Unless you have a SW broadcaster in your neighborhood you are picking them up via low angle skip where you want the antenna to have good low angle properties. If you run some typical wire antennas at low heights through an antenna analyzing program you will be surprised at the mostly straight up radiation they have.

If you set up the same typical SW wire antenna on the side of a hill with the hill tapering down and away from the antenna, it will pull the radiation pattern down some towards the horizon and in effect give you gain in the direction of the descending hill.

Or if you put a horizontal wire antenna at 1/2 wavelengths above the ground at your receiving frequency you will get lower take off angles and more gain at the horizon where you want it for distant reception.

Otherwise, for a horizontal antenna its all about how high the antenna is off the ground and very little to do with how high the average surrounding terrain is.

A vertical HF/SW antenna over a good ground plane will typically have a lower angle of radiation at the expense of picking up more noise.
prcguy

 

[WA8ZTZ]

Assuming that by "shortwave" you mean the HF frequencies, the short answer is "no", the increased elevation of the terrain you mention would not matter. (Actually, eastern Long Island should be an excellent trans-atlantic DX location).

Can't imagine the man-made RFI/EMI in NYC... it must be horrible. So, getting out of the city should yield a big improvement in the signal to noise ratio. If, as you mention, things did not improve out on Long Island, then my guess would be to blame propagation. It has been erratic at best lately on all bands from LF though HF.

The next thing is your antenna. You need a good outdoor antenna. Do some reading and experimenting with various antennas. All part of the radio adventure.

 

[dragon48]

Thanks for all of the replies and the confirmation that propagation has generally been awful lately. I seem to remember getting much better SW reception a few years ago. I'll have to go ahead nd get a good outdoor antenna.

 

[Boombox]

In my experience elevation can help only when "low elevation" equals "I have hills around me," i.e. when you live in a valley, as I do.

If you don't have any hills around you to block low angle signals, how high or how low you are shouldn't matter.

And yes, propagation has been terrible most of the past year, actually.

 

[WU8Y]

Terrain effects on HF reception are complex. The height of the antenna above the terrain, and the profile of the terrain close to the RX antenna in the direction of the incoming wave, can create effective gain or loss.

Absolute height above sea level doesn't matter so much as relative height of the antenna above terrain.

Consult the ARRL Antenna Book for a very in-depth discussion of this topic.