10W for local, portable emcomm?

Started by Tru, January 16, 2021, 12:03:39 PM

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Hey, I am studying for my ham licence and am joining my local emergency preparedness group. My question is around all these portable radios like the IC-705, the EX2/3,the new TX-500 (the current one I'm leaning towards) that are around 10W. I know others like the FT-817/8 are down around 5-6W and have a huge following. I live on one of the Gulf Islands between the mainland and Vancouver Island. Line of site is not very far in most directions, though there is a peak fairly close to me that I can get to the top of within an hour's walk. I'd like a portable setup for emcomm during a long term, grid-down scenario like after an earthquake. So a low power rig is what I'm looking for for using on solar power. I may also need to walk to the local school which is designated as our Emergency Operations Centre, or up to the top of said peak, so light weight and packable is important (I'd likely be carrying a lot of food, water, clothing and camping gear as well!). I'd be relying on a combi of ground waves and NVIS. The range I'm thinking I'll need for voice communications is only 100km or so to the local major cities and surrounding islands and communities. The government will supply a large VHF radio plus FRS radio they want me to use for acting as a hub and intermediary for neighbourhood contacts (on FRS) and then on VHF to police, fire, ambulance, emergency social services, coordinating boats for bringing supplies to, or people off the island, that sort of thing. But their solution doesn't let us talk with Victoria or Vancouver or other surrounding islands or communities that are not line-of-sight. Nor even other parts of our own Island. Hence working with them to set up NVIS. Those who have done a decent amount of QRP NVIS, is 10W good enough for *reliable* SSB using NVIS for 100km or so? And to the extent it's not reliable, would 20W or 100W make a significant difference if the propagation just isn't there? Eg. Does 10W work 95% of the time and 100W would work 96% of the time? If that were the case I would stick with 10W. Or would 10W work 70% or the time, 20W would work 95% of the time, and 100W work 99% of the time? That would make me get a 20W or potentially even a 100W capable tranceiver.

NOTE that I am planning on getting very good at building excellent antennas. Also, I know CW and data modes will work fine with 10W, thats not what I'm interested in - I want to know what power output is needed for voice communication capability, as CW and data will work at that power level too.  Thanks for your input!



This is a question with a complex answer that could fill a book... Yes, 10W can do it, no problem. Everyone will tell you it's impossible, especially emcomm people. The antenna and the way it is installed makes all the difference. Now, apprarently you are into emcomm, not survival radio... Big difference.

100km is a difficult range to cover. I would say NVIS on 80m and VHF SSB with a Yagi-Uda antenna. Between the two you should be ok, but don't expect 95% reliability. It's radio, not land-line telephone. You can't even throw numbers like 95, 99%, those are meaningless. 99% when? Where? How? Sometimes you'll get 100%, sometimes you'll get zero, as fancy as your equipment might be. Practice will teach you how to increase your reliability, not equipment.

In your case being on a hill is the key. You can go very far, even 100km with a 5W handheld VHF radio if you are high enough. A friend on mine made a 200-mile contact using a Yaesu VX1 with an output (using AA cells) of 100mW. We were at 2000m altitude near the sea.

Also look at the JS8 digital mode using the JS8Call software.



Hi Gil, thanks for the reply!

By reliability I'm asking how much of the time could I get a functional signal (they can tell what I'm saying without too much repeating) to someone 100km away using NVIS assuming a good antenna setup. Like if I transmitted continuously for 10,000 hours (just over a year), switching to the best frequency as needed, how many of those hours would I be recieved well. For emcomm, they know what frequency to look for me on, and they are actively looking for my signal. If I was received 5,000 of those hours, but for the other 5,000 they couldn't make out what I was saying, that would be 50% reliability for our purposes here.

And I'm not even interested in what that exact number is, as much as I'm interested in the *difference* in reliability you'd expect (best guess) between 10W, 20W, 50W, 100W, etc., since what I'm trying to decide is how much power I need to plan for, both in terms of which rig I get, as well as what I need to plan for in terms of batteries and solar panels and such. If I can get away with 10W but I planned for needing 100W, then I may have only spent a little more on my radio, and it may only weigh a couple pounds more, and I can just turn the tx power down, but instead of carrying 5lbs of batteries I'm lugging 50lbs, or instead of knowing I could have just spent $400 on solar panels I went and blew $4000. That's why I want to nail down the difference in reliability between the different outputs. And I'm asking here because I know people accustomed to high power rigs poopoo QRP when they've never used it or become proficient with antennas, or they're only interested in DXing or racking up the most QSOs.

So... Back to the question at hand... For example if 4 people (not on top of the mountain) each had identical NVIS setups (say each had a nice 40m dipole inverted V and reflecting wire under it), and they were each transmitting at the same, ideal frequency for the time of day (all changing at the same time), for 10,000 hours straight, but one of them was transmitting at 10W, another at 20W, another 50W, and another at 100W, what percentage of the time would each of them be functionaly heard (understood) by four other people who were listening for them that whole time 100km away. Would you expect the 10W to be understood closer to 900hrs (10% reliability) while you would expect the 100W to be understood more like 9,000hrs (90% reliability) with the 20W and 50W coming in perfectly where you'd expect? Then I'd totally plan on 100W! Or would the 20W, 50W and 100W all do about the same 90% reliability, but the 10W would be significantly lower - suggesting that there's value in bumping up to 20W but not higher? Or would the 10W actually be up around the same reliability (whatever that is) as the 100W?

It doesn't matter if 10W was 30% reliable and 100W was 32% reliable vs 10W being 90% reliable and 100W being 92% reliable, what I'm interested in is what you would expect the *difference* to be (only 2% in either of these examples, so may as well get the 10W).

Why I'm specifically asking is because most of the talk is around what can be done once in a while under conditions I'm not in (the example of being at 2000m using 100mW line of sight) or via different methods (VHF with a high power Yagi-Uda line of sight) or for different purposes (DX, or trying to rack up QSOs with random people, or higher powered 'ideal circumstances' emcomm, or TEOTWAWKI comms across the country). There is very little information on what's needed to make a functional, regional contact for emcomm in the worst-case-scenario (other than than advantage of using predetermined frequencies and times) eg:

- My house fell down in an earthquake and I have to bug out on foot with food, water, and camping gear in addition to my radio gear (radio setup needs to be light and small)

- Gas for generators ran out three days ago and I've only been relying on my hand-crank generator and a LightSaver Max since then (needs low power requirements)

- I'm trying to communicate with other volunteers who may not have or know how to use data and can't do CW (needs to be voice communication - maybe the operator who owns the equipment is sleeping and their mom is on and all she can do is use the PTT - it's an emergency remember, so that would be allowed).

- The person I'm trying to communicate with is on another island, not line of sight, 100km away.

- I got shtuff to do, kids to take care of, etc, I can't be bent over the radio for all hours repeating everything a kaxillion times, and I'd rather not hike up a mountain multiple times per day, but people are counting on me organizing essential things and conveying important info.

So in that scenario, what kind of power do I need to give me the best chance of fulfilling my role, while making some sacrifices to take into account the reality of the situation and the limitations that imposes? Is 10W all I need to still fulfill my role effectively, or will bumping up to a higher power really be worth it or even necessary to get the job done? Again, it's the *difference* in effectiveness between the different power outputs I'm interested in, not how reliable radio communication is in general, and I'm only interested in non-line of sight, non-digital voice communication, as I understand those other modes and their capabilities/limitations better.

If you tell me I need line of sight, and that NVIS isn't reliable enough for what I need, then I will plan for that hike with a VHF and Yagi-Uda. If you tell me 100W is what's needed for NVIS, then I will take that to my group and we'll look at making sure I have a desk at the emergency centre where I can plug into their power, or if you say the big jump in reliability is from 10W to 20W then I'll look at a G90. Or we may look at the cost for all the extra gear and power requirements and just go with sat phones! XD

Another route I could go, if 10W would be OKish but more would be better, is go with a 10W radio like the TX-500 and something like the Electraft KXPA 100 amplifier, which is also fairly portable if I can make multiple trips or can use a vehicle or something and will have enough power, but I could also leave it behind if it's too big and heavy and/or I wouldnt have enough power for it. That would be a flexible solution, but I wouldn't bother with that if 10W just isn't going to cut it, or conversely, if 10W would be enough on its own.

I just want a realistic solution, not a defense of any particular method or power output, or car salesman promises, which is what I see on a lot of other sites and videos and certainly on manufacturer websites. People may really depend on me to deliver in a very bad situation, so it may be a lot more than my pocket money or my pride on the line, and I'm trying to take that seriously and do my research. However the only real way to know this stuff for sure is to do it, and I'm just starting out. That's why I'm hoping for knowledge from those with first-hand experience on here with QRP and NVIS (like you, Gil).

Hope that's specific enough as I think that's the best I can do! Thanks!