A lot of the POTA parks in my area are in some pretty narrow canyons.  There are at least 10 within easy driving distance of my house that have never been activated.  Many of them are "twofers" that are trailheads or campsites within larger wilderness or recreation areas.

What's the best strategy for activating from inside a narrow canyon?  

I have an assortment of wire antennas, vertical antennas and vehicle mounted mobile antennas, but for now I am limited to running a 5W FT-817 for mobile and portable use.  I currently can cover 80m to 70cm with vertical antennas and 40, 20, 15, 10 with an end fed.  I have plenty of wire and a few different ferrite cores, and I'm willing to make wire antennas for other bands if need be.

So I guess the question is, what's the best band to use for late day to early nighttime operations from inside a canyon?  12:00 GMT is 6:00pm MDT here so I need to start activations in the later part of the day this time of year.  My gut says just use 20m and rig it as a low inverted V.

VHF/UHF might work if there were a bunch of POTA hunters standing on the canyon rim.  But the real challenge is going to be picking the right band not only for the time of day, but also for the ability to get a signal up and out of the canyon.

Can riding through these canyons with the car's AM radio tuned to a local station tell me anything of value?

I don't want to spend hours in a fruitless pursuit, but if there's a good chance at actually successfully activating some of these parks, I'd like to be the first to do it.

There's no way to activate them without going into the canyon? You only have to be on park property. The boundaries are in the canyons only? That's probably not going to be easy but people do it a lot.

Would be fun to try different NVIS antennas.  Probably won't get too far but it would be a fun experiment....

You will now get an extended thread about NVIS

Don't let all the NVIS posts overcomplicate your understanding of this phenomenon. It's literally as simple as:

1. NVIS in the USA exists 99.9999% of the time on 40M, 60M, and 80M depending on time of day.

2. You can get a good idea of the f0F2 frequency (maximum usable frequency, or MUF) at the current time of day at the following website. There is plenty of historical data so you can see patterns and make predictions.

https://www.sws.bom.gov.au/HF_Systems/6/5

3. Choose the band that is closest to f0F2 without going over. Of course if that is 60M you won't get many contacts because it is not a popular band.

4. Put up ANY, literally ANY, horizontally polarized antenna.

5. Put the antenna up less than 1/4 wavelength above the ground (the default condition for any portable 40/60/80M antenna anyway).

5W is not a good performer on NVIS. 20W is a practical minimum, but you might make some contacts. This has to do with D and F layer absorption, particularly in the daytime.

Contacts will be within a few hundred miles.

All that said, there is never any harm in trying any band at any time. HF is like a box of chocolates. You never know what you are going to get when you make things very difficult (low antennas, low power, poor terrain). If you try hard enough and long enough you will make a contact. If you want to "cheat", don't forget to spot yourself on a POTA spotting website. And then you can be the guy that says "Shoot, man, you don't need that fancy amp and tower. Hell, I talked to Australia on 100 milliwatts and a lawn chair. And then I won the lottery. Hand me another beer, boy!"

If you want to get really crazy, consider balloon-borne or kite-borne antennas.

With Cycle 25 hung up and it being mid-summer, 20 and 40 are going to be your best bet. As stated above, horizontal polarization and heigth of less than 1/4 wavelength will give you the high radiation angle needed to make contacts.

You can find additional Ionosonde data here: https://www.digisonde.com/
Select the Digisonde location nearest to you and select the year, month, day, and time for current conditions.
Some of the sites may no longer be operational, so you may have to select another.
If you haven't used an Ionogram before, there are numerous websites that will tell you what to look for and how to interpret it.

ETA: Our group did numerous Field Days from an island in the middle of a TVA lake (Watuaga) surrounded by steep mountains. We always had good results, not as good as on a mountain top, but still good results
Grilling our fresh-caught trout and sleeping out under the stars made up for it, though.

I have thought about this myself.   I can tell you this much, when I operate mobile on HF and going down the road, there are many dB's difference in signal strength with on ongoing QSO between the valleys and the hills. And the hills have it. It is the difference in "your down in the mud" and Wow!, you have a great signal. Yeah, that much. As far as "cheating" goes, there is NO cheating by spotting yourself on the POTA website. It is the norm to spot yourself before operating.

80 meter NVIS would give 300 miles coverage. That should work well out of the deepest canyon. 40 meter NVIS always seems hit or miss to me. Now all of that said, I live in a valley, but it isn't a deep valley, and have a couple of ends that are open to the horizon. But I can drive less than a mile to a hilltop and it makes a big difference.

Unless a miracle occurs, 20M is never going to provide NVIS propagation. And in the summer 40M is often not a good band for NVIS, either. Which leaves 60 and 80M for NVIS. Your own ionosonde link below shows this quite well.

However, there's never any penalty for trying to make long distance contacts on, say, 20M, out of a canyon location. Weird stuff does happen on HF.

That's a great link. I've always used the Aussie site, but the one you suggest looks great, too.

As noted above, here's the INL site data for this morning. 40M NVIS is just not there. Forget about it period on 20M barring the aforementioned miracle.

Attached File

Smoke Signals.

I'd start with a vertical on 20 and 40 and see how that works. You might be surprised how your signal bounces out of there.

I hate to say it, but I look at that graph and all I see is a school of suspended bait fish and maybe some walleye just off the bottom.  

Someone I know was planning on making a full wave 160 meter ground plane with balloons once. Next time I see him I'll ask if he ever did it.

RF energy has to go somewhere, but I am not sure QRP from the bottom of a canyon is an activation I would want to bet on making 10 contacts from. Good luck OP.

Click here: https://www.wirelesswaffle.com/index.php?entry=entry110112-212228
It looks intimidating at first, but once you think about it for a bit, you should be reading them like a pro.

Take some time to explore the other pages listed at the bottom. Believe me, it's well worth your while.

That's the long answer, the short answer is that you want a low height dipole for 80 and 40 meters and a 100 watt radio (at least) if you're down in a canyon.


40 is at the high end of the frequency spectrum for NVIS and often above the useful frequency range, but worth a shot especially if some lower takeoff angles are possible, I would imagine in most places you'd have takeoff angles down to 20~30 degrees at least.

Some of them could be activated from outside the canyons, but in many cases these are wilderness areas that don't allow mechanized access, and the only legal routes are the canyon bottoms.  If you wanted to activate from the rim, you're hiking in on foot.  It's about 20 years too late for me to do that kind of thing.  POTA is fun, but packing radios for miles would take the fun out of it for me.  I do appreciate those who do it from a hunter perspective though for sure.

So another question I had is, if you have a clinometer and can actually measure the angle from your antenna position to the canyon rim, how high is too high of an angle to get away with using 20m and a vertically polarized antenna?

You would be better off using a horizontal antenna 1/4 wavelength (5 meters ) high. It will radiate from straight up to what ever angle is the highest terrain clearance angle and maybe even bounce off the canyon wall and escape
the canyon, but with probably a large attenuation.

a vertical is going to have a very big hole in the radiation pattern above 45 degrees off of horizontal. A good grounded 1/4 wave vertical will have a 25 degree takeoff angle or lower.

It is a crap shoot.

Not much above 20 degrees on 20 meters... found this graphic:

Attached File


You really want that 9~10 degree peak if at all possible.

If you're really down in a hole you're not going to hear much on 20m or higher.