VHF Radio Propagation and APRS

[metrologist]

I am using a 1W APRS transceiver set to beacon my telemetry data about once a minute when I am using the device (AP510). This is going to be an FM modulated digital tones.

My signal always gets into an iGate when I turn the unit on inside my building, usually to a relay station 15 miles away on a hill, then to an iGate 20 miles away in the other direction.

I  go outside and walk a few miles and no signals make it to the relay station. I hold the device over my head and beacon, and NO signal makes it onto the network. How is that physically possible?

I clip the device on my motorcycle handlebar and drive an hour around, going within miles of an iGate and other relay stations, and no signal gets into the network.

I verified there is RF out by using a SPA about 10 feet away and still seeing 0 dBm signal after a few hours of beaconing.

I am going to string a upright v dipole from my helmiot and see how it works.

Another thought occurred and that may be that the iGate stations are just rejecting my signal. I noticed there are some mobile stations that get into one iGate instead of another that is closer. I wonder if some of these iGates are using pl tones to be a bit more "private". Maybe the one that picks me up has some programming to only allow one transmit signal.

I need to figure out what the problem is, RF side or something else. It's just strange the way it's working inside only and consistently when I expect the building to obstruct, and then being outside closer to the stations and nothing. ?

Gee there are a lot of weather stations. About one every mile or so in some small regions around here.

[TheDane]

1W on 144MHz ought to go a long way.

Does the iGate see other APRS traffic?
- also from afar and consistently?

(What I'm asking - Does it have an excellent antenna, so it's not the cause of your problem, that the iGate is blind and not sending your data to the relay station on the hill - are they on the same frequency btw?)
I can listen and transmit to the local APRS repeater indoors on my handheld Wouxung on high with it's small rubber antenna - and on low power using my normal indoor 50/144/433MHz antenna, and it is is located several KM's  (10+) from here.

I have noticed that APRS/Packet signals can be a bit tricky to adjust. Have you build the hardware yourself. Try to demodulate the signal using an SDR dongle, there's a lot of software that can do the decoding realtime. (C-sharp with plugins) A 1200/2200Hz tone tweak might do the trick, as it is intermodulating or getting clipped and causing distortions in the TX section. Works ok close, but craps out at distances. It could also be the iGate that has trouble detecting the FSK signal (1200/2200 Hz)

A duplex repeater function on 144MHz requires filtering you'd never believe, also at more moderate power levels. Just ask any local ham person with repeater responsibilities, so if your iGate are on different frequencies than the relay and there's TX traffic going on - you have the reason right there. (And possibly the solution  )

[metrologist]

My understanding of APRS is that the frequency used is region specific. In North America, all APRS stations should be on 144.39. Digipeaters will receive and then repeat the same digital stream on the same frequency it was received, in a serial fashion.

I am looking on APRS.fi website. One thing I cannot determine is what are all the stations? I know there is a code used for your icon and I do not see a place for me to change that in my device software. Anyway, some stations show up as a star with a letter, some are diamonds with a letter, some are a big fat X, many are car icons, and the most, by a factor of at least 10, are WX stations, everywhere!

Ok, when I hover over a car icon, I see a path to a green star with an "I" in it 10 miles away. The path continues to a star with a D in it another 20 miles away, which happens to show it is an digipeater and igate. There is a star about 500 feet away from the car icon that says it is a digipeater and igate too. Why the signal makes hops rather than going right to the nearby station? What about all the other dozen stations that are closer than 10 miles away? Is it like a sperm when penetrating the egg, there is a signal to not allow any more sperms inside the network?

But more importantly, my signal should be received by any of the numerous stations around, and it only seems to go to one station and relays to another a much further distance away. I just wonder about all those other stations around and why the signals seem to make the same hops to the same stations. Also, I have programmed Wide 1-1 Wide 2-2 and I never see any more than one hop from a station (that I would think is already an igate) to another igate. It seems a statistical improbability that my signal will consistently make it onto the network from inside my building every time I turn it on without fail, at least once, but have less than 1/100 the connection rate when outside wandering/riding around with the antenna out in the open air, held over my head, across long distances, past many stations... Makes no sense whatsoever.

My device is a commercial AP510 APRS digipeater device sold by some Chinese or Japanese mfg. called SainSonic. Details of the device are easy to find on the website. I do not think there is a malfunction of the device, but rather I need a better understanding of the APRS system and why it's not working for me. I suspect there is a lot of traffic and signals are interfering, and my signal is very weak to start with. Even so, the generalized performance does not make sense to me. I'd also like to understand aprs.fi better, like what do the icons really mean? How can I find all the igates around me? What symbols to they use. I do not see a legend on that site, which seems so incredibly odd. Who makes a map with a bunch of icons and no legend, especially someone smart enough to put such a system together?

[TheDane]

I live in Denmark, Europe - here the APRS signals are supposed to be on 144.800 MHz
SUPPOSED....... It's just digital signals, which are well within the packet data space limits on the 2m band, if you follow rules&regulations.

The 2meter band (144-146MHz) is regulated, and in order to transmit legally one needs a licence.
The licence/call signal is the info which is sent to the APRS network, and signals YOUR location. (There are different addendum options, Callsign-M for mobile operation, etc.)
I guess it's possible to get dispensation or a temporary callsign for scientific missions, schools and organizations etc.

I know not the model you refer to, but one thing that might be the issue is that everybody else is using some kind of kit/hardware that's not responding well to your signals, hence a tweak is needed either on your end or theirs.
If you have access to a local ham club, they might be able to help you adjust the signals if need be - or verify that you're indeed using the correct tones.
I pick up a LOT of activity when I tune to 144.8 Mhz, which my old TNC-2C decodes without problems. Adjusting the TCM3105 makes all the difference though (TCM3105 is a modem - http://www.netti.fi/~ryydis/tcm3105.pdf)

There are lots of possibilities why your setup is misbehaving. I can't answer them, but help you in certain directions. No feedback =

[TheDane]

Btw - not everything is created equal.....

Googling APRS kits yields 390.000 results! 
- some are made using PIC or Atmel microcontrollers, using 2-3,4,5 bit discrete outport ports as the Digital-Analog converter. The Analog/Digital part is done through some other means, either the built in A/D port or ".........secret-sauce........"hardware

Most are running some standard frequency xtal on top with wildly fluctuating accuracy, and I'm sure the resulting FSK signal has a bad THD (Total Harmonic Distortion) which blows any HiFi nerd to a different planet, while the core is generating and decoding the FSK signal (Software modem functionality) while doing other house-keeping stuff like talking to GPS/UART etc.
- but they talk nicely to each other, I'm sure 

[metrologist]

I understand the general details about Ham radio, as I've been licensed for 15 years.

The specific module I'm using, but no affiliation:

https://www.sainsonic.com/two-way-radio/ap510-aprs-tracker-vhf-with-gps-bluetooth-thermometer-tf-card-support-aprsdroid.html


Aside from this, the device seems to work well. It picks up more APRS traffic than my GT-3 (same as the UV-5R) and decodes it and sends it via bluetooth to a generic bluetooth serial terminal on my phone. I should be able to send outgoing messages the same way.

Anyway, I think I see one possibility is that some of the stations I see on aprs.fi may not be listening on the national aprs RF frequency. Those would be blasphemers and I'm sure not tolerated for long around here, but that is a gentlemanly thing I'm sure, and of course no violation to send/receive aprs encoded messages on any frequency a ham is authorized to operate. I just think it may be a condition to connecting to the aprs server, but not sure. It's not the issue anyway...

I was just looking at the area around Middlefart for a comparison of the area. There are many less stations around that area, about 1/100. Of course I cannot tell what most of the stations are around here.

I have test equipment and rtl-sdr, maybe I could fiddle around with getting some decoding. Or I think I used to decode the demodulated audio using UIView (which I think I cannot get to work anymore).

[TheDane]

  for 15+ years

Then I'm sure you have a 144 MHz Power Amplifier Module - have you tried to hook it up after the APRS. It's only 1W output, ideal to drive say, a 10W output.
A better antenna with good SWR, and a field drive or two - and that will take care of the question: Why indoor, and not far away outdoors. The output power level of the module is faulty or wrongly adjusted?
(Come to think of it, a 50 ohm load dump could test it indoors, but what's the fun in that  )

I know bluetooth signals love metal in walls, which reflects the signals. A large conducting flat device out in the open, and (microwave is very much directional) the 2.45GHz antenna on it's rear has very poor coverage in front of it, if there's nothing to reflect the energy back.
Perhaps your building has some kind of amplifying effect, much akin the function director elements serves in a regular 2meter directional antenna, letting the signal transfer easier to the iGate/Relay Network.

[TheDane]

I verified there is RF out by using a SPA about 10 feet away and still seeing 0 dBm signal after a few hours of beaconing.

I remember you mentioning measuring 0dBm at 10 feet, at 144MHz.
10 feet is around 3.3 meters, which is 'too close to comfort' if you ask me, because you're in close proximity to the transition window measuring possibly both electric fields and magnetic fields.


Quote from Wikipedia:
"The near field and far field are regions of the electromagnetic field around an object, such as a transmitting antenna, or the result of radiation scattering off an object. Non-radiative 'near-field' behaviors of electromagnetic fields dominate close to the antenna or scattering object, while electromagnetic radiation 'far-field' behaviors dominate at greater distances.

Far-field E and B field strength decreases inversely with distance from the source, resulting in an inverse-square law for the radiated power intensity of electromagnetic radiation. By contrast, near-field E and B strength decrease more rapidly with distance (with inverse-distance squared or cubed), resulting in relative lack of near-field effects within a few wavelengths of the radiator."
https://en.wikipedia.org/wiki/Near_and_far_field

1W output power should be 30 dBm - measured directly across the output in a 50ohm system.
[dBm]   [Watts]            [Volts]rms            [Volts]p            [Volts]pp
0           0.100E-02      223.607 mV          316.180 mV      632.360 mV   
30         0.100E+01     7.071 V                 9.998 V            19.997 V   
http://ifmaxp1.ifm.uni-hamburg.de/DBM.shtml

Have you measured raw output power, or transmitted power at a distance - compared to a known 1W device?

[Lord of nothing]

  I dont understand why nobody use DMR Radio. The most have a GPS Receiver and can transmit the Position and also Text Messages. 

[TheDane]

I dont understand why nobody use DMR Radio. The most have a GPS Receiver and can transmit the Position and also Text Messages. 

Have you built one yourself?
- it's not as easy as it might sounds.

APRS uses pure analog RF signaling, and most people can make their own device if they're motivated.
DMR has tons of variants, so have fun designing your own solution which is compatible with everything&ease - and please do share it, as you are right - it's newer, and better if enough uses it (but this is the thing with all new tech) 
(With the setup/adjustment instructions, etc. naturally) 

[Lord of nothing]

  so would you walk with a backpack full of radio stuff around? 

[metrologist]

This device is a complete APRS transceiver and is the size of a pack of playing cards - smaller than any DMR radio I've seen. Cost and complexity, and that the APRS infrastructure is already built and in heavy use, is why I wanted to play with it. I have only been lightly exposed to DMR a couple years ago and there may be a great opportunity there*.

I have not measured another 1W signal. I assumed that the RF signal works initially as my transmission is picked up from far away when I power up the radio. I just wanted to verify that the PA was not overheating and shutting down, so I did not observe a degradation in signal intensity, and the RF envelope looked good. A level of 0 dBm is what I would expect given my crude setup - the radio was not directly connected to the SPA.

I have downloaded a couple pieces of software (replacements for UIView and AGWPE), one is a soundcard modem that will decode the AX.25 tones. I will use my own radio with audio fed into my PC and record my own transmissions, and get an idea of signal intensity if I can determine how to measure that (with the tools I have).


* DMR and DStar both seemed too much like my cell phone and using the Internet. The aspects of what made radio radio seemed to be missing. Kind of like when they took away all the coin slot machines and made them electronic, with a printout receipt of your winnings instead of the streaming coins spilling into your bucket. Took the fun out of it and I haven't been back to Vegas since.

[metrologist]

I set up my RF network using my GT-3 HT with a straight patch cable from the speaker output to the mic input on my PC. I'm sure there is mismatch there, but fidelity through the PC speakers sounded good.

I started UG7HO soundcard modem and it sporadically decoded APRS traffic. I'd say less than half of the received signals would decode.

I started APRSIS32 and enabled the AGW port and that completed the setup. I was not going to transmit or relay the information onto the internet, but APRS-IS was connected.

I was amazed at how far some signals traveled. One came from 400 miles away and a couple others were from the 100+ mile range. Nobody was within 20 miles.

I went on a walk test and only a hand full of points showed up on my local map. I checked aprs.fi and only 3 out of about 15 transmissions were captured. One of my home points and the same two points farthest away showed up on my local map and on aprs.fi.

I became disappointed because my local map was also plotting data received from the APRS-IS server, so I do not know if any points were decoded by my local modem, except the few that were not on aprs.fi. I also observed transmissions that I decoded, but that did not appear on aprs.fi. So, given that my close signal is decoded less than half the time and other signals are decoded less than half the time, and the network does not receive all the signals I receive, then I conclude that the entire system just performs poorly.

[TheDane]

so would you walk with a backpack full of radio stuff around? 

./me is not -m (mobile ham) much, if at all. I prefer stationary operation, doing mostly technical stuff - talking/listening just for 'fun', no thanks - the tech stuff is much funnier 
But surely, for mobile applications an easy to use water proof radio is absolutely something to go for.  I have a cheap Wouxung radio, and it's the best handheld I've had so far though it's not so easy to program out in the field, and then I have my homemade ones - but it's hard to compare the two types imho 
(Day car vs. drag racer - both move people on a road)

Besides, where's the fun in buying everything - and fixing it if/when it eventually breaks 

[TheDane]

I went on a walk test and only a hand full of points showed up on my local map. I checked aprs.fi and only 3 out of about 15 transmissions were captured. One of my home points and the same two points farthest away showed up on my local map and on aprs.fi.

I became disappointed because my local map was also plotting data received from the APRS-IS server, so I do not know if any points were decoded by my local modem, except the few that were not on aprs.fi. I also observed transmissions that I decoded, but that did not appear on aprs.fi. So, given that my close signal is decoded less than half the time and other signals are decoded less than half the time, and the network does not receive all the signals I receive, then I conclude that the entire system just performs poorly.

So there's consistency. Great 
I suggest you look into how the antennas are at the APRS repeater network/iGate setup. If they use directional antennas, you might be located in a deaf spot.
Does the country side change much, such as in height difference, valleys, plantation, large moving objects or other things that can disturb the radio waves.
Clouds can also have a big say - http://rsgb.org/main/get-started-in-amateur-radio/operating-your-new-station/vhfuhf-propagation/

You might be able to test your home station/setup by changing frequency and the APRS update refresh rate, and getting some fresh air again      [No noise/Ch. Clear]

[metrologist]

This is not the consistency one would hope for.

Just for something to do, I had considered using a quiet frequency for a test, but I would also expect 1W to full quiet anything else on the air since I did not walk very far away - within 600 meters... Even two ducky antennas at body level should be sufficient with a watt. Maybe I will try a better radio than the GT-3 and think about a matching circuit (I think an 8 ohm load might help, or I have the right transformer laying around somewhere). In the end, I still need to get into the other iGates, so I think bumping up to 5W or more will get this out of the grass and give it some hope. I may even pull out my 4 element antenna elmer direct connect Yagi.

The terrain is varied with hills and valleys. Most of the iGates, or the one's I am hitting have omni antennas. One is 16 km away on a roughly 700 meter high summit with antenna 160 feet up in a dense wooded area. I am at sea level next to a large body of water and am staying pretty much on the flat lands or lower foothills.

[Nerull]

so would you walk with a backpack full of radio stuff around? 

[TheDane]

What a beauty 
My guess you 3D-printed the case, did a small lithium powered job with gps and basic hmi is done through oled and the front buttons. 
The output, is it high UHF?

[TheDane]

Just for something to do, I had considered using a quiet frequency for a test, but I would also expect 1W to full quiet anything else on the air since I did not walk very far away - within 600 meters... Even two ducky antennas at body level should be sufficient with a watt. Maybe I will try a better radio than the GT-3 and think about a matching circuit (I think an 8 ohm load might help, or I have the right transformer laying around somewhere). In the end, I still need to get into the other iGates, so I think bumping up to 5W or more will get this out of the grass and give it some hope. I may even pull out my 4 element antenna elmer direct connect Yagi.

I would expect 1W FM to cut through most noise as well - which was why I suggested checking the output of the transmitter stage. It might be faulty, or the reading you did was flawed somehow?

Regarding region and land:
Most APRS units have bad RX performance, if they listen to the frequency at all. Units can, due to not being able to hear, cause disruptions on an already ongoing transmission - and many be why you get so many bad packets (diamonds and other signs - I presume your terminal is set to the right encoding type like "normal" ANSI, others are possible like VT-100, etc. I'm sure you know this, but it's a forum 
You mentioned earlier that you had checked the region around Middelfart, I presume here in Denmark, and said that there was little traffic. Is there a lot of chatter on the main frequency, when you listen on it? It could sound like there is, and the packets are just colliding - and higher output power is not solving the problem, but making it worse. (Solution - more frequencies, less users) Ah, I remember the old days with packet and getting news and files through 1200 baud simplex. It was a French program, it could auto-merge files, and a ton of other features. The name evades me at the moment  It was a great way to propagate stuff, as the user didn't have to login to the BBS and request the info 'privately'.

[Lord of nothing]

I have a cheap Wouxung radio, and it's the best handheld I've had so far though it's not so easy to program out in the field, and then I have my homemade ones - but it's hard to compare the two types imho 

Try some TYT MD-390. Water resistant and there are Versions with GPS Available.

I prefer stationary operation

Why APRS on an stationary Station? 

The output, is it high UHF?

Looks good but the outputpower is limited.
Here in Austria you can also use 433.800MHz/ 432.500MHz 

[Nerull]

What a beauty 
My guess you 3D-printed the case, did a small lithium powered job with gps and basic hmi is done through oled and the front buttons. 
The output, is it high UHF?

I only wish that it was mine, I just did some looking for APRS small beacons.

My point was just that APRS beacons don't need to take up a backpack, and can be smaller than a DMR. APRS is also a well established system and has many integrations that DMR lacks. For example, storm chasers use a website called spotternetwork to report their positions. This can be done over the internet, but it can also track callsigns on APRS, so when operating in areas without cell data coverage someone can still monitor where you are. There is no similar system for DMR, and DMR repeaters are not as widespread.

[Nerull]

Why APRS on an stationary Station? 

APRS can transmit more than position, and is common for weather stations.

[metrologist]

I set this up on another laptop that has no internet connection.

Two early morning walk tests and I captured 90% of my own transmissions (18/20). Afternoon tests and that dropped to just about 50%. I was also using a Larsen dual band antenna on the base station. I receive a transmission about once every 5 seconds, sometimes less and sometimes I hear stations transmitting over others.

My APRS module does receive, but I do not know if the software accommodates that for its beacon.

I need an overview of using the APRSIS32 software. I was getting a chat request, somehow I lost track points, and I did something to enable seeing an RF path. One station from far away seems to hit a close base station, which relays the signal to another base station closer to me that then sends the signal to me (3 RF legs). I think that was the chat request. I was not seeing the RF paths of the other stations. I had about 50 stations on my map in an hour.

Now I think I will set up my Yagi in the direction of the mountains I want to hike and do some more testing. That's going to take a while to get set up, and it will be more activity for the summer.

[TheDane]

I set this up on another laptop that has no internet connection.

Now I think I will set up my Yagi in the direction of the mountains I want to hike and do some more testing. That's going to take a while to get set up, and it will be more activity for the summer.

 
Good luck, I hope you fix the issue by getting better coverage - it sounds like the channel is congested and the units are really disturbing each other.
UHF APRS.... Austria, really.. I would think the VHF signals would go propagate better in a mountainous country, so better coverage or more free space on the air?
I haven't looked into UHF APRS, but a Texas Instruments CC1101 immediately pops into my mind - what a neat solution. Software/hardware defined protocols and SPI interface. China sells the modules dirt cheap. Rx/Tx in almost no space. What a shame I'm already busy with so many other fun things.