Mobile NVIS Systems (ex- 6m v. 10m)

[Boyscoutdreams]

No. NVIS will not work on other bands. That is a restriction of the NVIS technique. It only works on the 80-40 meter band. SSB with 100 watts (or less) and a long whip bent over the car should provide reliable com with a 500 mile radius. Omni-directional antennas will not provide reliable com at that range. Commercial SW/HF/VHF/UHF broadcasters don't get that range, reliably, with 50,000 watts. Occasional skip and skywave will do that range and more, but don't count on it when you need it.

I don't know of any other way to achieve reliable com at that range for mobile use. NVIS 40-80 meter WILL do it, without a doubt. With digital modes or Morse code it could even be done with 5 watts or less.

Thank you. I knew there were some frequency restrictions but was not sure what they were. What I like is these restrictions are physical, not legal (except the license part). I like it when wiser people fill in the gaps that I know I have with better details.

Edited to add- Mobile can be car mounted,,,,, but portable can be strung up where ever needed so you don't have a huge long antenna hanging on the car all the time. Talk about standing out while driving down the road. But they both can be done successfully.

[TacAir]

Voice only, I live in North Central Iowa and want to talk to Northeast Arkansas, 525 miles direct path. I plan to learn morse so CW is an option, provided my brother learns it as well, which I doubt he will.


EtA: Not sure on snow gauges in AR... no offense.

Just examples to show MB comms are in use every day.

The PARS folks are active in your AO - did you have a chance to look at that link?

[CitizenZ]

I was actually contradicting these types of posts, not yours.

If we're talking about NVIS antennas, shouldn't we also be talking about MUF?

No. NVIS is not dependent on MUF. NVIS is basically THE method between ground wave (direct) and sky wave (skip) propagation methods. Its' frequency is dependent on the technique, not your MUF/LUF. Although NVIS sometimes works on higher and lower bands, generally reliable com will only be achieved on 40-80 meters with NVIS with a 500 mile radius.


Since 525 miles is on the edge of range, you can cheat this a little by having your NIVS lean a little in your favored direction instead of straight up creating an oval shaped zone instead of a true circular pattern (not really centered over your location). Simply turn your whip/wire to have the tip angled toward your target. A 2 or 3 element yagi aimed straight up or angled slightly down towards your target can improve range between 2 fixed points. Experiment with polarization at both locations as well. With the mobile it might make more sense to have the whip go from back to front. Almost all the energy is "launched" from the tip, not the base, so the alignment of the top few feet of the whip is the critical factor.


Another added benefit for CW is that it would only require a technician license and a cheap CW radio, while voice and data would require at least a general class license to use 40-80 meter bands and a more serious/expensive SSB radio.

[CitizenZ]

Voice only, I live in North Central Iowa and want to talk to Northeast Arkansas, 525 miles direct path. I plan to learn morse so CW is an option, provided my brother learns it as well, which I doubt he will.


EtA: Not sure on snow gauges in AR... no offense.

Just examples to show MB comms are in use every day.

The PARS folks are active in your AO - did you have a chance to look at that link?

The problem with MB com is that it is only useful for burst, usually scheduled com lasting only a few seconds. They require directional antenna, repeated transmissions until a good copy is achieved, and the sources I've read recommend high power and/or dedicated MB type software. Not really useful general use com, but can be useful for specialized scheduled long distance communication, that acts like satellite com, without the satellite. NVIS will be really slow with data/images, but MB would use higher VHF/UHF frequencies and allow more data in a few seconds than HF would in an hour.

Because these ionization trails only exist for fractions of a second to as long as a few seconds in duration, they create only brief windows of opportunity for communications

[44Dave]

I was actually contradicting these types of posts, not yours.

If we're talking about NVIS antennas, shouldn't we also be talking about MUF?

No. NVIS is not dependent on MUF. NVIS is basically THE method between ground wave (direct) and sky wave (skip) propagation methods. Its' frequency is dependent on the technique, not your MUF/LUF. Although NVIS sometimes works on higher and lower bands, generally reliable com will only be achieved on 40-80 meters with NVIS with a 500 mile radius.

I'm pretty sure MUF is the reason why you have to (generally) stick to 80/40 meters. If you go too high you punch through F2 and you don't get the reflection.
Athens ARC has always seemed to have the best information about NVIS techniques.
AB0PC is decent as well.

Second, MUF, or maximum useable frequency, the highest frequency we can use and still achieve good reflection/refraction off the F2-layer.

It's how I learned it anyway

[TacAir]

I was actually contradicting these types of posts, not yours.

If we're talking about NVIS antennas, shouldn't we also be talking about MUF?

No. NVIS is not dependent on MUF. NVIS is basically THE method between ground wave (direct) and sky wave (skip) propagation methods. Its' frequency is dependent on the technique, not your MUF/LUF. Although NVIS sometimes works on higher and lower bands, generally reliable com will only be achieved on 40-80 meters with NVIS with a 500 mile radius.

I'm pretty sure MUF is the reason why you have to (generally) stick to 80/40 meters. If you go too high you punch through F2 and you don't get the reflection.
Athens ARC has always seemed to have the best information about NVIS techniques.
AB0PC is decent as well.

Second, MUF, or maximum useable frequency, the highest frequency we can use and still achieve good reflection/refraction off the F2-layer.

It's how I learned it anyway

FM-24-19
Section VI. NVIS Antenna AS-2259/GR

http://www.globalsecurity.org/military/ ... 19/Ch3.htm

I used the As-2259 in Alaska and in the Western US with the PRC-104 and the PRC-47, gave very good results in broken terrain. Used a 1/2 wave dipole in flatter terrain. For field use, great, for mobile, not at all.
Army TM with theory of operation.
http://hilltoparmyradios.com/as-2259-man.pdf

http://www.dxengineering.com/pdf/NVIS-Rev2.pdf
While selling a kit they make, the article gives precise directions for making a copy of the AS-2259. Well worth the time to look over.

http://n3oc.dyndns.org/Homebrew%20AS-2259%20GR.pdf
provides detailed step by step DIY directions with photos


Fair Radio sales had these some time back fro 150 USD.

http://www.zombiehunters.org/forum/view ... 42&t=70765 earlier thread.

[North Force]

The SMC Mobile HF Loop Antenna, developed for NVIS (Near Vertical Incidence Skywave) communication across 3-15MHz, overcomes these limitations by having high radiation efficiency and no skip zone whatsoever.

http://www.smc-comms.com/nvis_transport ... ntenna.php

[KJ4VOV]

The SMC Mobile HF Loop Antenna, developed for NVIS (Near Vertical Incidence Skywave) communication across 3-15MHz, overcomes these limitations by having high radiation efficiency and no skip zone whatsoever.

http://www.smc-comms.com/nvis_transport ... ntenna.php

Any idea on the price range of these?

[North Force]

If i remember correctly - it's around $4500. Something like that.

[KJ4VOV]

If i remember correctly - it's around $4500. Something like that.

Well, the wife has drawn the line at adding anything to the truck that costs more than the truck did, so I may have to pass.

[CitizenZ]

Lol!

I'll build you one for half that price (with a straight face), in about 2 hours with scrap parts from my shed.

You can build one for a few bucks.
HF loop tuned to 40-80 meters, insulated mount, DIY balun, paint and $4300+ profit.

[KJ4VOV]

Lol!

I'll build you one for half that price (with a straight face), in about 2 hours with scrap parts from my shed.

You can build one for a few bucks.
HF loop tuned to 40-80 meters, insulated mount, DIY balun, paint and $4300+ profit.

Oddly enough, I just came in from the garage where I was looking to see what parts of such an antenna I might already have handy. That motorized mount would be nice though for erecting it. Climbing to the roof of my truck and doing it manually is gonna be a pain in the ass.

[Bunsen]

Lol!

I'll build you one for half that price (with a straight face), in about 2 hours with scrap parts from my shed.

You can build one for a few bucks.
HF loop tuned to 40-80 meters, insulated mount, DIY balun, paint and $4300+ profit.

What do you use for the high-voltage variable capacitor? Those are generally a bit hard to find (or unpleasantly expensive) and a real pain to retune when you QSY. Seems to me that most of that amazingly high price goes into the automatic capacitive tuner.

[CitizenZ]

Lol!

I'll build you one for half that price (with a straight face), in about 2 hours with scrap parts from my shed.

You can build one for a few bucks.
HF loop tuned to 40-80 meters, insulated mount, DIY balun, paint and $4300+ profit.

What do you use for the high-voltage variable capacitor? Those are generally a bit hard to find (or unpleasantly expensive) and a real pain to retune when you QSY. Seems to me that most of that amazingly high price goes into the automatic capacitive tuner.

An MFJ tuner (949E I think). Built in variable capacitor, balun, dummy load, meters, switches, etc. I got it at a hamfest for $20. Building custom traps and matching devices without a proper antenna analyzer stops me from most experimental designs, unless I can do it with a standard tuner, balanced or unbalanced, then it's cake.

[Bunsen]

Lol!

I'll build you one for half that price (with a straight face), in about 2 hours with scrap parts from my shed.

You can build one for a few bucks.
HF loop tuned to 40-80 meters, insulated mount, DIY balun, paint and $4300+ profit.

What do you use for the high-voltage variable capacitor? Those are generally a bit hard to find (or unpleasantly expensive) and a real pain to retune when you QSY. Seems to me that most of that amazingly high price goes into the automatic capacitive tuner.

An MFJ tuner (949E I think). Built in variable capacitor, balun, dummy load, meters, switches, etc. I got it at a hamfest for $20. Building custom traps and matching devices without a proper antenna analyzer stops me from most experimental designs, unless I can do it with a standard tuner, balanced or unbalanced, then it's cake.

Have you tried that with small magnetic loops? I'd be afraid of arcing with a normal air variable at moderate (100W) power levels and the astronomically high SWRs involved. But if it works, more power to you (heh).

[fourpaws]

Have you thought about splashing out on a CODAN system ?? It operates on the low to mid HF range and is ruggedised for military, NGO and civlian use. I can testify to its ability from using it in Iraq and Afghanistan to communicate all over the country.

The antenna is attached wherever you want to put it, the RF unit is cabled through the vehicle dashboard and is normally kept under one of the seats out of the way. Everything is run from the handset which is easy to use.

With the NVIS kit, large comms distances can be achieved. The TUAM (Tuning Unit, Antenna Matching) or the Horn on the front/rear of the vehicle is a good unit and provides a full range of frequencies that you may need. Ive attached URL's and pics below for you to have a look at if youre interested.

http://codanradio.com/OurProducts/Transceivers/NGTSRx/Features/tabid/686/Default.aspx







Hope that this helps.

'Paws.

[Tater Raider]

It does help. A lot. Here's the question:

This system is going on the vehicle pictured below. How far above the vehicle do I need the antenna to go?



I'm figuring the lack of sheetmetal is going to affect the antenna height.

[TacAir]

Uff-dah.

If you are going to rig a high power HF transmitter with an over the 'roof' antenna, you should read this as well.

http://transition.fcc.gov/oet/rfsafety/rf-faqs.html
It is also applied to Amateur Service radio operations as well. See FCC ET Docket No. 93-62


Here is a link to do the math.
http://hintlink.com/power_density.htm

[KJ4VOV]

Unless he plans to run an amp and do a heck of a lot of FM, AM or RTTY he should be well within compliance for a controlled area, seeing as the majority of amateur mobiles rarely exceed 100 watts PEP stock out of the box.

[Tater Raider]

I wasn't thinking safety. I was thinking groundplane.

Holy birth defects Batman!

[coldshot]

I wasn't thinking safety. I was thinking groundplane.

Holy birth defects Batman!

Now back in my Army days as a tanker, I had an antenna like this within a meter of my head. Are you trying to say that Uncle Sugar wasn't looking out for me? Maybe the CVC acted like a Faraday cage. And, yes, that is a USGI 1911A1. We were still carrying those in the early 90's believe it or not.

[Tater Raider]

Okay, assuming safety isn't an issue, groundplane? Am I good-to-go or should I lower the antenna? Also, since I roof-top a canoe which side of centerline should I relocate the antenna and how far can I move it sideways before I start really screwing it up?

[North Force]

While you would fold it over your truck on the road - when stopped, you can just use the ground as your ground plane... like so

[Tater Raider]

Okay, I think I have the basics and some ideas of how to install it now. I'll be working on my licenses starting mid-June and should have something up and running by next summer.

Thanks muchly!