Powering mobile radios in the field

[bkt]

For anyone interested in powering a small HF rig or a 2m/70cm mobile rig in the field, here's a pretty low-cost solution that, so far, has worked great for me. This Miady 12.8v 16Ah LiFePO4 is a bargain at $45.99, and this 12v 2A charger is also affordable at $20.99. Total cost with shipping was under $75. That's a pretty good price for a 16Ah battery. The weight is just under 4 lbs.

I've used it with my Xiegu G90 HF radio as well as my BTech UV-50x2. The G90 puts out a max of 20W so I can easily get a full day's use out of a charge if I'm not doing a continuous duty-cycle (digital or CW). The UV-50x2 puts out up to 70W on 2m, so not as long a run time there but still good for a fairly long period of time. Setting the rig to low power (30W) gets me a good long time - most of a full day.

 

[BadgerLandHunter]

For anyone interested in powering a small HF rig or a 2m/70cm mobile rig in the field, here's a pretty low-cost solution that, so far, has worked great for me. This Miady 12.8v 16Ah LiFePO4 is a bargain at $45.99, and this 12v 2A charger is also affordable at $20.99. Total cost with shipping was under $75. That's a pretty good price for a 16Ah battery. The weight is just under 4 lbs.

I've used it with my Xiegu G90 HF radio as well as my BTech UV-50x2. The G90 puts out a max of 20W so I can easily get a full day's use out of a charge if I'm not doing a continuous duty-cycle (digital or CW). The UV-50x2 puts out up to 70W on 2m, so not as long a run time there but still good for a fairly long period of time. Setting the rig to low power (30W) gets me a good long time - most of a full day.

Being a tech myself I own several baofeng UV-5Rs that I bought before it was "illegal" being an HT you don't get the power but I figure I can give them to my family and maybe connect with other Ham friends who have agreed to meet on a specific freq if SHTF happens.
Best part is they were cheap and I bought the extended batteries that lasts over a day of mostly monitoring and some listening. Just remember watts are only as useful as the antenna sending them. I see so many people talk about how many watts they have then have a cheap junk antenna.
I agree though 2 way radios will be very useful IF people use it right and don't stomp on each other. In fact becoming a licensed ham is cheap and easy. To be a tech or general class you no longer need to be able to do Morse Code.

 

[bkt]

If you're interested in longer-range and more reliable communications on 2m, set up your own cross-band repeater. Something like a TYT TH7800 that puts out 50+ watts and will act as a cross-band repeater, and a decent dual-band antenna like a Tram 1481 and you're set. Make it a portable repeater with the battery shown above and maybe add a solar panel and charge controller so you don't have to swap out batteries.

You're right that watts don't count for much if you don't have a good antenna and ideally some elevation as well. So if you do set up a repeater, plan its location intelligently. By the way, I found this site, Radio Mobile Online to be pretty useful. It produces propagation maps, taking topography into account, that are reasonably accurate.

 

[Bacpacker]

Thanks for the link BKT. Looks like some useful info.
And you are spot on about using cross band repeating. Works like a charm. Our EmComm group used it frequently on a bike ride we supported up in the mountains. We had a several mile stretch that was a dead zone for RF. Used a Topo map and found a couple of likely sites to try. One of them filled in the dead zone except for about 1/4 mile. We could live with that.

 

[SheepDog]

For getting the most output is it generally better to use a directional antenna? Assuming the antenna is aimed toward your target what is the best?
YAGI, dipole, "V", inverted "V", or rhomboic?

 

[bkt]

Good question, and I don't know. I'd be inclined to try a Yagi first, since they're easy to build. I've never seen a rhombic antenna and don't know how they stack up to a Yagi. The others you mention are usually associated with HF rather than V/UHF, but I'd be curious to learn how they can be used on those higher frequencies to direct power.

 

[SheepDog]

I used to use a rhombic antenna on 80, 40 and 20 meters - for receiving only. Inverted "V" has a higher signal to noise ratio but I don't think it is particularly directional. The dipole is slightly less directional (bi-directional) than the rhombic but was THE standard for CW for a long time even with VHF. Air Force emergency radios were equipped with di-pole antenna at least through the Korean war. I've been away from the field for a long time so what is current now I have no idea.

 

[bkt]

Thanks, Dog. Directionals like Yagis are popular with line-of-sight frequencies - VHF and UHF. Dipoles, endfeds, and their configurations (inverted V's, NVIS, etc.) are usually used with HF. I've had really good success with a G5RV - it's a dipole with a long ladder line - in an inverted V configuration. Normally, you would orient a horizontal antenna along the compass to cover the largest populated area. I'm in the northeast, so an East-West orientation would cover the whole Eastern seaboard for me. As it so happens, I have it North-Northwest to South-Southeast and I get a very big area of the country.

 

[SheepDog]

Glad to hear that some things don't change.

 

[Bacpacker]

I'm not familiar with Rhombic types. Yagis are the highest gain of the ones you mentioned. And yes much more in use on VHF/UHF freqs. But they are made for any band thru 40M. But they are HUGE.
Long wires of any type are not much better than bi directional. But they are fantastic for what they do.

 

[BadgerLandHunter]

Exactly not as long of a set up but the HTs I have are dual band so I found a video on how to set them up to make a portable repeater. Though it wouldn't be as nice without a battery and solar panel. Yeah that woul help a lot the HTs put out like 4 watts if your lucky on high so a boost would help.....on a hill.

 

[bkt]

Exactly not as long of a set up but the HTs I have are dual band so I found a video on how to set them up to make a portable repeater. Though it wouldn't be as nice without a battery and solar panel. Yeah that woul help a lot the HTs put out like 4 watts if your lucky on high so a boost would help.....on a hill.

If you're going to experiment using two HTs, an audio cable, turning on VOX to receive on one frequency and transmit on another, be aware that the antennas need to be separated by a few meters to prevent desensing on the receiving radio. I learned about this the hard way.

 

[SheepDog]

The rhombic antenna is mono-directional. Twin leads connect the two sides of a horizontal "V" that is coupled directly to another horizontal "V" with converging ends. Common usage had a terminating resister at the converging point but a capacitor reduces the very small side lobe propagation to almost non-existent. The only transmission is out the far end of the diamond shaped antenna in a tight pattern best suited to a point to point communication. It can be used for frequencies from 80 meters up to UHF. Tuning the capacitor can increase or decrease the side and point radiation. The antenna receives best in the same direction that it radiates from. The down side is that each of the four legs of the rhomboid should be at least 1/2 wavelength. That is not too big if you are using 2 meter but at 80 meters it requires a large area approximating the length of a football field and about 2/3 as wide. Support poles to keep the antenna on plain yet high enough to avoid ground interference adds to the difficulty in construction. They work well for long distance sky wave communication as well as point to point.