VHF Distance From Pikes Peak?

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I recently received this question via email from Dave N0MUA:

Bob, I ran across your pictures mountain topping on Colorado peaks, thought if anyone could answer this it would be you and your group.  We run on 146.52 here in Coffeyville KS.  and a group of us have brought up the question how far east can a mobile atop Pikes Peak be heard on 146.52 FM? The mobile would be mine running a Icom V8000 into a Tokyo HI power amp at 375 watts  LMR 400 coax to a Cushcraft 13B2 beam pointing to the east.

This is one of those how far will my signal go? questions that always gets my attention. Other folks may find this interesting, so I decided to spend some time on the topic and post it here. I am assuming we are talking about tropospheric propagation and not something more exotic such as meteor scatter or sporadic-e skip.

The (incorrect) conventional wisdom is that VHF propagation is “line of sight”, extending a bit beyond the optical horizon. From Wikipedia, we find that the distance to the optical horizon can be approximated by:

d = √(1.5 h)

where d is the distance to horizon in miles, h is the height of the observer above ground in feet

Pikes Peak reaches to 14,110 feet above sea level. The elevation of the surrounding area varies but since Dave is asking about propagation into Kansas, let’s use a typical elevation of eastern Colorado (4500 feet). This gives us an optical horizon equal to the square root of (1.5 x 9610) = 120 miles. Yes, this is an approximation, so feel free to knock yourself out with a more precise calculation.

It is interesting to note that there is a community 30 miles west of the Kansas border called Firstview, CO that is supposed to provide the first opportunity to see Pikes Peak when traveling from the east on Highway 40. Firstview is about 135 miles east of Pikes Peak, so the 120 mile calculation is in the right ballpark.

The ARRL web site says that the radio horizon is about 15% longer than the optical horizon, so that means our line-of-sight radio horizon is about 1.15 x 120 = 138 miles. I’ve operated from the summit of Pikes during the ARRL June VHF QSO Party and the Colorado 14er Event and working stations on 2 Meters at this distance is not difficult. To be more specific, I worked the Mt Sunflower crew (highest point in Kansas, 160 miles) from Pikes Peak on 2 Meter FM using a 25 Watt mobile and a not-very-well-positioned 1/4-wave antenna on the SUV fender.

I pulled up the distance records for the Colorado 14er Event and found that the best DX using 2 Meter FM is when Phil N0KE on Mount Bross worked Larry N0LL in Smith Center, KS at a distance of 375 Miles! Clearly, we are well beyond line of sight for this radio contact. N0LL has a very capable VHF station on his end and I believe N0KE was using a decent Yagi antenna and was running some power(~200W?). Still, this contact was on FM which is not that great for weak signal work. While Pikes is on the Front Range of the Rockies, Mount Bross (14, 172 feet) sits back some distance, about 60 miles west of Pikes Peak. (I have also worked N0LL from Pikes using 50W and a single 2M9 yagi on SSB with no problem during VHF contests.)

Also during the Colorado 14er Event, Phil N0KE (and Jeff N0XDW) on Mount Bross worked W7XU in Parker, SD on 2 Meter CW at a distance of 551 miles.  Keep in mind that as the signal strength fades, SSB has a serious advantage over FM and CW is even better! So for squeaking out the marginal contacts, CW is the way to go.

Dave asked about working Pikes Peak from Coffeyville, KS using 2 Meter FM. I had to look up where Coffeyville is and discovered that it is way the heck over on the east side of Kansas, maybe 50 miles from Missouri. I estimate that Coffeyville is 525 miles from Pikes Peak. To get back to Dave’s question, making a contact from Pikes to Coffeyville on 146.52 MHz FM is not likely. Maybe if we got some exceptional tropospheric propagation…but I think even then it would be unlikely to complete the contact using FM.

But you never know what might happen on VHF. That’s what makes it fun.

73, Bob K0NR

4 Replies to “VHF Distance From Pikes Peak?”

  1. An interesting analysis and comment, but may I suggest a different method? Radio Mobile by VE2DBE produced accurate coverage plots determined by topography and the capabilities of stations at each end. In our densely populated island the repeater coordination system does this automatically to ensure that chaos does not ensue. I used it 5 years ago when moving house to see what kind of a radio site I was buying.

  3. I received this via email (RMVHF email list) from Phil N0KE:

    RMVHF
    When I worked Larry, N0LL, in EM09 on 2m FM from Mt Bross I was running either 160w or 350w to a 13 EL KLM. We also tried 222 FM (140w to 14 el KLM) and heard each other but no official QSO resulted. No problem to work Larry on 432 CW. On 2m CW we also worked W7XU who has a well equipped VHF contest station in EN13SE South Dakota, his wife Holly N0QJM(?). We heard another station in the same grid but in the NE corner of IA but he couldn’t copy us. On another occasion I heard a station in central Iowa on 432 CW but he never heard my 100w and long yagi and he was running some serious power and good antenna.

    During a CSVHF conference in Colorado Springs one summer there was a very stable mass of hot air going east from Colorado and some exceptional tropo. I was running 100w to a 4 el 2m yagi mounted on my vehicle’s spare tire bike rack and my first QSO was near South Bend IN and I was just barely above most of the homes in Colorado Springs. I worked stations in MO, KS, NE, IA, IL, IN, MI, WI and the opening lasted until about 11am on Saturday and Sunday. Two VHF stations in the Colorado Springs area worked 432 tropo as far as Columbus Ohio. Tropo like this rarely gets as far west as the populated areas of the front range of Colorado.

    If I was going to make a special trip from eastern KS to Pikes Peak, I advise using the planned power and antennas on CW and if conditions are really good you might make it on SSB with a bit of tropo help. I would be nice to do it the same weekend as the 14er event. I think the tropo is there more than a lot of people realize as few or maybe no one monitors 144.200 on a regular basis. Doug, W0AH (now K4LY in SC) use to live near Woodland Park at the base of Colorado used to monitor FM and TV broadcast stations to the east of Colorado and found many cases of tropo that hams did not take advantage of. Some of this well into the UHF TV channels.

    During this tropo one station from MO was at the VHF conference and on Saturday morning after he got wind of the tropo, drove to the top of Pike Peak and was above the tropo for some time as those of us lower down were in it. We lost it and for over an hour worked a lot of station to the east in the same states I worked plus MN and maybe some others. Dave was running stacked loops and 100w and many of the stations he worked on SSB in MO etc were running 10w to small yagis. Stacked loops don’t offer much gain and are omni directional.

    Phil N0KE DM69em

  4. Even on 10 GHz SSB, from the top of Pikes Peak, you can consistently work into Wyoming 150 miles away. And that’s with a very modest 2 Watts and small dish on each end. A 2 meter FM contact between the same two stations is easily accomplished with mobile whip antennas and 25 Watts. That’s picking two locations that have clear views to one another (but not a visual line of sight), so pretty much an ideal situation. As always, local topographical or man-made obstructions will reduce the range, so as we all know your mileage will vary depending on various factors.

    Gary WB5PJB DM79oi