Tropospheric ducting?

[Bugkiller]

Got a new HT, charged it up, and started playing with it.  Normally, I hear crickets, or kids playing with bubble wraps.  Not tonight.  Long conversations on 462.650, obviously on a repeater.  All well and good, except…

There are no repeaters on that frequency near me.  

Signal was fading in and out.  Finally got the repeater id and tracked it down.  It belongs to a repeater 130 miles (as the crow flys) away.  On a tower about 330 ft.  I’m in Florida, so its is relatively flat.  

I’m new to the radio game, but I’m thinking I was picking up tropospheric ducting this evening.  What say you experts?

[marcspaz]

Wrong time of the year for traditional ducting... but we have a geomagnetic storm that is starting.  It's going to peak in about 2 days and expected to last for a few days.  Last time I was in Florida and this happened, I was able to talk from St. Pete to Panama City Beach for several hours a day several days in a row.

 

During geomagnetic storms, more often than not, UHF radio waves get absorbed, causing reduced range.  Other times UHF can get reflected like HF NVIS propagation.  The easiest way to tell if that is happening now is if you have a GPS system that relies solely on SatComms (not cellular) and you are having accuracy issues or an outage.

 

There are some websites that map this stuff out, too.  Been a long time since I looked for them, though.

 

EDIT:  This tropo map is indicating that you may be right... how about that!

 

https://www.dxinfocentre.com/tropo.html

 

[WROZ250]

11 hours ago, marcspaz said:

Wrong time of the year for traditional ducting... but we have a geomagnetic storm that is starting.  It's going to peak in about 2 days and expected to last for a few days.  Last time I was in Florida and this happened, I was able to talk from St. Pete to Panama City Beach for several hours a day several days in a row.

 

During geomagnetic storms, more often than not, UHF radio waves get absorbed, causing reduced range.  Other times UHF can get reflected like HF NVIS propagation.  The easiest way to tell if that is happening now is if you have a GPS system that relies solely on SatComms (not cellular) and you are having accuracy issues or an outage.

 

Tropo ducting is also a weather generated phenomena.  When I lived in the Midwest, it happened more often than it does down here in the Southwest (if it happens at all here).  It typically impacts VHF and UHF communications. 

It is not unheard of to have contacts in the hundreds, even 1000+ miles under the right conditions.  Pretty cool when it happens, but despite the prediction tools, nobody really knows for sure where or when it is going to happen.  It's kinda like predicting tornadoes... you know the 'conditions' are present, but that doesn't mean it's going to happen.

Back in the 1970s, there was a repeating pattern in the weather every morning for about a week.  It was so strong, it was causing ham repeaters in Chicago area to lock up with repeaters in the Detroit area (Michigan used repeater input and output frequencies inverse to what Illinois used. Normally not a problem). 

In any event, despite being somewhat disruptive to local communications, it was fun because for about 3 hours every morning, you could hear (and QSO) guys in Detroit during their morning commute and vise-versa. 

The police had issues with it because many departments (on shared frequencies), that would normally be far out of their respective communications range, now had to deal with and sort out traffic from multiple agencies.

I've not seen a Tropo incident of that magnitude or duration since.  Indeed, typically Tropo ducting is a very short in duration, but that too depends on the weather!

 

[MichaelLAX]

Was that on 2 meters or 440 MHz?

[WROZ250]

58 minutes ago, MichaelLAX said:

Was that on 2 meters or 440 MHz?

The 1970's event? 

That was primarily 2 meters, but there were a couple of UHF guys saying they experienced some ducting as well.  I personally, didn't have any UHF equipment at the time, so I cannot say for certain that UHF was enhanced by the event.

You gotta remember that back in the 1970s, operating UHF was just getting popular in amateur radio, at least in the Midwest.  Most of the people I knew who were on UHF were doing SSB and CW (and then usually with transverters) so if there was any tropo ducting going on at UHF, they would probably know it.  As I recall, there were only like 20 UHF repeaters in the Chicago area back then.  Today, you can't find an unassigned pair. A lot changes in 50 years!

Tropo can and does happen at UHF, but I think it far more rare than at VHF.  That said, that mid 1970's event was extraordinary by anyone's measure.

 

[WROZ250]

15 hours ago, Bugkiller said:

Got a new HT, charged it up, and started playing with it.  Normally, I hear crickets, or kids playing with bubble wraps.  Not tonight.  Long conversations on 462.650, obviously on a repeater.  All well and good, except…

There are no repeaters on that frequency near me.  

Signal was fading in and out.  Finally got the repeater id and tracked it down.  It belongs to a repeater 130 miles (as the crow flys) away.  On a tower about 330 ft.  I’m in Florida, so its is relatively flat.  

I’m new to the radio game, but I’m thinking I was picking up tropospheric ducting this evening.  What say you experts?

Not saying it wasn't tropo, but it sounds more like normal/typical path margins. 

I routinely monitor a GMRS repeater in the Las Vegas area which is about 90-95 miles away from me.  Most days the signal is pretty decent, other days it has a lot of 'popcorn' on it.  I also have a few mountains between me and Las Vegas and the overall terrain is desert with a lot of temperature variations throughout the day, all of which get reflected up into the atmosphere (RF path).

There are a lot of things that can make or break a path, especially at UHF.  Don't know where in Florida you are, but as childhood memory serves me, it's pretty humid there. 

One thing known to eat (attenuate) UHF signals is water vapor (not sure if salt in that vapor contributes).  So it is possible that there are 'weather related events' that might be altering the moisture content along the path between you and the repeater.

Weather is not the only factor either.  Again, when stretching the proverbial rubber-band (long distance paths), a lot of things come into play.

Finally, flat is a relative term.  That 330ft tower at 130 miles away isn't actually 330ft anymore where that path is concerned.  More like 86ft relative to you at 130 miles away.  That probably allows for more path obstructions to come into play.

Again, there are a lot of variables involved.

So, forget all that mumbo jumbo and just have fun on the air!

[PACNWComms]

3 hours ago, WROZ250 said:

The police had issues with it because many departments (on shared frequencies), that would normally be far out of their respective communications range, now had to deal with and sort out traffic from multiple agencies.

I recall many of these types of incidents in the past. It was great when radio networks became "smarter" (and re-banding helped) as radios would then only affiliate with sites in their own network (SystemID). As you also mentioned, now it is hard even getting a UHF frequency pair assignment. Trying to get a pair for a dense RF environment right now. 

On the Tropospheric ducting aspect, I also worked tropo communications terminals in the military, with many experiments in prediction ducting, then came a company that bounced radio traffic off of meteorites. Lots of fun but esoteric types of propagation techniques. Washington State ferries to my north even had a statewide location reporting system based on the meteor bounce company, and two generations of that system were put into use. I am not sure if that is still used now, but it was an interesting technology to hear about, detecting a meteorite and using its ionized trail to bounce radio signals off the tail. Seemed to work for burst transmissions.

[WROZ250]

4 minutes ago, PACNWComms said:

On the Tropospheric ducting aspect, I also worked tropo communications terminals in the military, with many experiments in prediction ducting, then came a company that bounced radio traffic off of meteorites. Lots of fun but esoteric types of propagation techniques. Washington State ferries to my north even had a statewide location reporting system based on the meteor bounce company, and two generations of that system were put into use. I am not sure if that is still used now, but it was an interesting technology to hear about, detecting a meteorite and using its ionized trail to bounce radio signals off the tail. Seemed to work for burst transmissions.

I'll start by saying the military has a lot of technology not accessible to the average American. LOL!   That said, today there are software applications used in Amateur radio made specifically for bouncing signals off of the ionized trails given off of meteors, usually data bursts (which is probably what your ferries example were using) because it's not like these sort of paths last very long, at least not long enough for a typical voice transmission.  A fractional second data burst can convey more information than a 3 minute voice message, especially when you factor in forward error correction and automatic retries.

Technology is pretty cool, but sometimes it is just nice to sit back and actually talk to someone!

[AdmiralCochrane]

Meteor trail and moon bouncing are common with VHF guys chasing confirmed long distance contacts.  I am not certain any of the 20 or so hams that have made contacts with all 50 states on 1.25 meters did not use one or the other for some of their contacts.   Bouncing a signal off the moon is called EME, for Earth Moon Earth.

A lot of specialized equipment involved, high skills and PATIENCE.

 

I have heard ducting from NYC to MD several times, conveyed along the edges of weather fronts, which is similar to true tropospheric ducting where the radio signal is trapped in a temperature inversion, the same temperature inversions that can transmit mirage visable images across hundreds of miles. 

[gman1971]

Well, 130 miles on UHF using 50W coming from an antenna placed 330 feet seems doable, depending on terrain of course. I've read in many instances that 100w placed 100 feet in VHF will reach ~100 miles... so... triple the height will reach a lot further.

G.

[marcspaz]

There is a propagation method called troposcatter that you can use to intentionally talk 300+ mile on UHF, repeatedly and somewhat predictably. 

 

If you use high gain parabolic antennas on both ends and aim the beam at the horizon or just above, in the direction of the other target station, the signal scatters off of objects in the atmosphere. A small portion of that scattered signal gets refracted back to earth and heard by the receiving station. Because only a small amount gets refracted, the more power you use and the higherthe gain on the antennas, the higher the likelihood of success.

 

While it does occur in the 450MHz to 500MHz space, the 2 GHz space yields the best success. 

[OldRadioGuy]

I had a good case of ducting once back in Nov. of 1986.  I had just moved to my new house in Greenfield (southern NH) and put on the portable TV to test the signal.  I was relieved that I was still getting the Boston MA and Manchester NH channels OK - but there was another rock solid channel that I was not familiar with.  I watched for a while and it turned out the be Burlington, VT which was shocking.  That's 160 road miles away with mountains in between.  It just didn't seem possible but there it was - rock solid.  

I had only moved about 20 miles further up from my old place in Milford NH.   I'd never heard of anyone getting Burlington TV around southern NH.  It was not a TV repeater channel either.  It was the Burlington channel direct.  It was probably 9 or 10pm at night. 

The next morning I tried it again and it was nowhere to be found.  Tried it a dozen more times and nothing but blank screen.  It was just a case of ducting that came and went. 

Vince

[WROZ250]

10 hours ago, gman1971 said:

Well, 130 miles on UHF using 50W coming from an antenna placed 330 feet seems doable, depending on terrain of course. I've read in many instances that 100w placed 100 feet in VHF will reach ~100 miles... so... triple the height will reach a lot further.

G.

Love It! 

That was one of the statements radio sales people used to suggest coverage expectations back in the 1960-1980s, in the days before coverage prediction software, "100W , 100ft, 100 miles"!  And as you say, (depending on terrain) that was generally a true statement for VHF (high and low).

 

[gman1971]

7 minutes ago, WROZ250 said:

Love It! 

That was one of the statements radio sales people used to suggest coverage expectations back in the 1960-1980s, in the days before coverage prediction software, "100W , 100ft, 100 miles"!  And as you say, (depending on terrain) that was generally a true statement for VHF (high and low).

 

Well, remember this tower in question is 230 feet higher than a 100 foot @ 100 watt on VHF... and for UHF height is pretty much the most important factor if long range is desired...

[PACNWComms]

33 minutes ago, WROZ250 said:

"100W , 100ft, 100 miles"!

I remember those days as well. Now it is "1 watt, 1 mile" for the more honest. I still get a kick out of the blister pack FRS radios that claim up to 28/30/32/46/50 miles, when that is under very ideal conditions at best, top of mountain to base of mountain.

[WRVD382]

Not sure that this is the right topic to discuss inversions. Retired now but worked in mining prior. Due to the location of our operations it was a requirement to receive a daily weather report that had inversion information. If the inversion was below 3000-3500 feet at our location we rescheduled  our blasting operations. Also inversion ceilings would change as the temperature increased. I now wonder if this would affect our radios at times. Also inversions are more likely to occur in colder weather. Could this affect our radios? 

[marcspaz]

14 hours ago, WRVD382 said:

Not sure that this is the right topic to discuss inversions. Retired now but worked in mining prior. Due to the location of our operations it was a requirement to receive a daily weather report that had inversion information. If the inversion was below 3000-3500 feet at our location we rescheduled  our blasting operations. Also inversion ceilings would change as the temperature increased. I now wonder if this would affect our radios at times. Also inversions are more likely to occur in colder weather. Could this affect our radios? 

 

Temperature inversions and inversion levels are what causes the refraction (largest impact on the refractive index), lending to what we call Tropospheric Propagation and Tropospheric Ducting. 

 

Makes sense to postpone blasting when there is an increased risk of high power(ish) RF in the lower atmosphere.

[WRVD382]

Good information Marcspaz. Just to clarify the inversion information was used to eliminate the effect of the air blast hitting the temperature ceiling if it was too low and rattling some neighbors windows. Not really a pleasant experience getting phone calls after a blast. The blaster also used a wireless box to transmit a signal to another box that was closer to the blast area. The previous method was all wired. 

However we used mostly Kenwood radios for the business and now looking back I wonder how much effect this had if any on transmissions. The site was small but due to at the deepest part of the pit say 600' we would sometimes experience signal loss. Mostly relied on a "human repeater" to cover distances. So I guess my question would be could we have been having good/bad days with radios due to inversions? 

[marcspaz]

7 hours ago, WRVD382 said:

So I guess my question would be could we have been having good/bad days with radios due to inversions? 

 

Not in your specific example, no.  There should be no correlation.  While ducting occurs adjacent to the surface, your communications is localized and likely had/have stations that are too close to each other and too low of an elevation to really be impacted.