Single band vs dual band value

[ultraclyde]

I spent some time searching the forum but couldn't hit on anything that really addressed this, so forgive me if it's a rehash.

I just got my call sign earlier this week and I'm already thinking about upgrading from my mobile-rigged HT to a real mobile unit. My question is about the usefulness of having a dual band vs a single. My limited exposure in this area (SE US) is that almost all traffic is on 2m. Although there are some 70cm repeaters they aren't active, or they are just crossbanded from the 2m. A Decent Dual band mobile unit will cost around $350 (give or take) and put out around 50 watts. OTOH, you can get a rugged single band 2m that puts out 80 watts for around $170. 2m typically gets a little more distance than 70cm too, as I understand it, although that's highly dependent.

So, my question is - For off road, overlanding, and general outdoor use, is having 440Mhz/70cm more valuable than having an extra 30 watts of transmit power?

All this is assuming a good power supply, a quality Diamond antenna properly mounted, etc, so that you can actually make use of the extra wattage.

 

[Hillbilly Heaven]

A dual band radio is more than just 2 bands. Some of the dual band radios will do more than just vhf/uhf at the same time. I prefer models that will do V/V, V/U, U/V, and U/U. This way I can monitor two 2 meter repeaters at the same time or monitor a 2 meter repeater and run APRS at the same time.

That extra 30 watts is not that noticeable.

 

[dreadlocks]

I'd suggest a used Kenwood TM-281 for $70 or less, its milspec 65w with great sensitivity and filters..

Ive got a dual bander temporary setup in my tow vehicle waiting for a perm install, but thats because I modified it to access GMRS frequencies.. when I'm not in a caravan using GMRS I usually use the dual recieve on 2m.. so I can do packet and voice at same time, never really tried to work 70cm on the road..

Around here, 70cm is used mostly for digital signals (bbs, 9600 baud, link nodes/backhauls, etc), atv, and some city repeaters because 2m is heavily used.. once you get out in the back country, its largely silent.

 

[Scoutn79]

Personally it depends on your intended use.
IMHO, and as you mentioned. 2m is the most widely used. The other bands are nice if you want more frequencies to choose from and the possibility of better privacy when using the radio. 2M meets all of my needs just fine.
On the wattage point I disagree with Hillbilly. The extra 30 watts is more important than the extra band(s). The extra power only matters when you need it. If your group stays close then 5watts is just fine but get into the hills and get really spread out or have an emergency and need to hit a repeater 60 miles away and it could make all the difference.

A quality antenna properly set-up, SWR tuned and good coax is just as important as the radio. It is a system.

Darrell

 

[Hillbilly Heaven]

The Db gain is not significant between 50 and 80 watts. The difference in gain is so small that it can be replaced with antenna gain which will also help receive. I would rather have a 50 watt dual band radio with a 6 db gain antenna than an 80 watt radio with a 3db gain antenna. The difference between 50 watts and 80 watts is 2.04 Db not even enough to move the S meter.

 

[ultraclyde]

If your group stays close then 5watts is just fine but get into the hills and get really spread out or have an emergency and need to hit a repeater 60 miles away and it could make all the difference.

This is why I'm asking. I seldom run with a group, usually it's solo fire road adventures. The radio is really a backup to the cell phone if something bad happens.

 

[prerunner1982]

A 2m monoband will certainly get you by and be sufficient. When I was looking for my first mobile radio I too was leaning towards a 2m only radio to save a few $$, but then I learned that the largest linked repeater system in my state was on 70cm and decided having the capability to do both would be a good thing. In GA is may not matter much however I do see that SC has a linked repeater system that includes a number of 70cm repeaters, (https://www.repeaterbook.com/repeat...system=SCHEART System&state_id=%&type=systems). There is a 70cm linked repeater system in TN that also has a link in KY and AL. (http://www.scara.net/repeaters, http://shoutsouth.com/) Depends on how far you plan to travel I suppose.
The ability to do cross-band repeat is nice too if you wanted to step away from the vehicle with an HT in hand but still want to hit a local repeater.
Another benefit of a dual band is that most of them have remote heads which makes mounting them in a vehicle much easier.

 

[DaveInDenver]

Could be regional, 70cm is fairly active here. Also being able to monitor 70cm is handy for FRS/GMRS. If the question how best to spend money, I would suggest a known quality, well built single band you can trust over an unknown or questionable dual band. But if you're budgeting and can afford a 2/70 it's better to have and not need IMO. For example, here in western Colorado, eastern Utah there's a system of linked 70cm repeaters that are nice to have access to.

Range increase is roughly the square root of the power gain (called the inverse square law). So going from 5 watts to 50 watts (a 10 dB increase) will gain you about 3.2 times the range, SQRT(50/5). Going from 50 to 80 (a 2dB increase) will gain you in theory SQRT (80/50) = 1.26 times the range.

Put another way to double your range you need 4 times (or 6 dB increase) the power, to triple your range you need 9 times the power, etc.

So when comparing transmitter power also remember to factor in coax loss (RG-58 is about 0.5 dB per 10 feet), connector & antenna mismatches (e.g. poor SWR) and antenna gain to figure out how much range you might have in theory.

 

[prerunner1982]

But don't do all the work Dave mentions....... and then mount the antenna on your bumper or fender. If you want range get the antenna up high. In LOS (Line of Sight) communication, height is king.

 

[ultraclyde]

Good discussion guys, thanks. It sounds like 70cm is still prevalent, but maybe not around here. (Or, I'm a newbie and haven't run into it here yet. Also possible.) Although there are no plans, I'd love to travel out west eventually. I'm thinking there's a good case for going dual band, plus I like the idea of the remote face mount. I never thought about crossbanding from a HT to a repeater, that's a big plus. I'd rather spend a little more and spend it once.

Antenna will be one of the Larsen/Diamond/Comet high gain half waves and it will be mounted on the roof of the Jeep. It's problematic given that most of our trails here are tree lined and brushy, but I'll dig into spring mounts when the time comes. Should be okay.

 

[Mtn Mike]

Yes, it's very regional. I never use 70 cm in my area but it's nice to have it as an option when traveling. I don't know what radio you should get but here's one more "pro" to single band radios, and this is purely my opinion; If you look at radios from the four "reputable" radio manufactures (Kenwood, Icom, Yaesu, Alinco), their single band radios are more robustly built than their dual-band radios. To me, the multi-band radios feel more like toys and the single band radios feel more professional. My guess is that this is because the single band radios are in fact, built on the same chassis as the professional line radios from these companies. But I've never had a radio from the big four fail me, either single or multi-band.

 

[ultraclyde]

I went on a trail ride with a group this weekend. Everyone had different comm systems, but we finally settled on using an FRS channel and gave walkie talkies to the 2 guys that were still CB-only. It worked out really well. That experience alone will keep me in a dual band receiver since the FRS channels are in 70cm. It seems like the best license-free workaround for mixed groups since the WTs are cheap enough to carry some spares.

 

[ultraclyde]

Incidentally, I looked up the specs on my cheap Nagoya UT-72 1/4 wave antenna. It's listed as over 3dB gain and capable of up to 80 watts, so it's better than what I thought. I haven't measured SWR on it, but I may throw a better mobile unit in with it and see how well it works. It's nice to have a little more clearance up top.

 

[Hillbilly Heaven]

Sorry but that is marketing hype specs not true specs. A 1/4 wave antenna has 0db gain or unity gain regardless of the frequency or band. A true 6db gain antenna will be 5/8 wavelength long. A 1/2 wavelength antenna will have 3db gain.

 

[DaveInDenver]

Sorry but that is marketing hype specs not true specs. A 1/4 wave antenna has 0db gain or unity gain regardless of the frequency or band. A true 6db gain antenna will be 5/8 wavelength long. A 1/2 wavelength antenna will have 3db gain.

The antenna he's talking about is 1/4λ on 2m and 5/8λ on 70cm, so the gain claim could be for the 70cm side.

https://baofengtech.com/NAGOYA-UT-72

There's other issues with the marketing, like that it's even 5/8λ. If I had to guess it's just a 1/4λ on 2m and doesn't appear to have any coils, which would mean likely it's actually 3/4λ on 70cm, which has around 2dBd of gain (or 4 dBi).