Keeping the HT cool

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Now that I’ve got everything working properly finally, im faced with another issue, or, maybe its not an issue, my Baofeng UV-5R gets really warm.

I had the TOT set for 30 seconds, but i noticed that it cut off conversations, especially on a net, so i reset it to 120.

Now it doesnt cut off conversations, but when listening to ragchews, the radio is on when one party is TX, and then it goes right back to TX again as soon as the other party keys up to reply, so th

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e radio barely gets a chance to catch its breath, and gets quite warm quite quickly.

I notice that alot of node builds use a UV88 with the case removed and a fan applied to the node housing for cooling, but my setup (so far) is just a UV-5R connected to a G1LRO universal radio controller which is connected to a Raspberry Pi 4b. Im not suse what exactly to do to really cool it down, or operate/set things different so it doesnt heat up to begin with. The TX power out is set to low of course on the UV-5R.

Any suggestions?
73

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HT’s are not normally designed for more than 50% duty cycle.
Some more and some less.
If you have the option to set it for lowest power operation of 100mw or 500mw
That might go a long way to reduce the heat you are generating.

If that 100mw/500mw is not enough power for your needs, I would then suggest using a external ht amplifier that you can extend the cooling externally.

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As i say, its a baofeng uv-5r HT radio, and its set on low power.
I jave no idea how many mw that equates to.

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You are now discovering why so many BF-888S mods include disabling the PA and running just the exciter power.
I once had a node modified in this way, and it could transmit for hours at a time without really even getting warm. Of course, it only put out about 20MW or so, but that was fine for going around the house and property. For more than that, I’d use a better radio.

1 Like
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Do you have a link to such a modification?

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You have to figure, the HT is transmitting all the time when it is used as a node. It isn’t actually just receiving when it’s receiving. HTs are simply not designed for that, even on low power. You can try a fan to dissipate the heat, but even that might not work.

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Well if thats the case, why is everyone advertising an allstarlink build using a baofeng UV-888?
Whats the solution if an HT is not appropriate, and why does everyone build them if they dont work properly?
One would think that there is a super low power transceiver unit that is available for such an application that would be popular.
73

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As was mentioned above, either most people are likely not utilizing the PA, or they’re burning up their radios. A fan might work fine. Hard to say.

There are super low power units that are available. Clearnode is an example.

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Do you have the mod instructions for bypassing the PA on the baofeng radio?

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I don’t. I don’t use those radios, though I have seen them modded before. If there’s no specific info on the web, you would probably just have to pull the schematic and go from there.

Honestly though, if you don’t care about a $20 throw away radio (I certainly wouldn’t), I might not do anything. If the PA burns up, it burns up. That’s kinda where you would be anyway after disabling the PA.

What I would probably at least try is have a fan blowing on it. You could use a fan like you have on the Pi in the pic. A large computer fan might do enough to keep it cool-ish, and should stay quiet enough. Way back in the day when I used a handheld for cross-band repeat (basically the same principle as what’s going on with your setup), a couple computer fans were plenty to keep the radio cool enough, even on high power.

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I have a Baofeng UV5R running at high and even on nets it stays cool enough. I do have a fan on it and was about to take the case off so I am actually cooling the radio and not the case. A Peltier module could help you. But they tend to have a bit of humidity so it might be an alternative but also something that you will have to figure out how to get the humidity out.
Just a thought.

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I just had mine running for about 10 minutes, some guy was ragchewing for a long time, and the radio got quite hot, especially the antenna connector. Its an older UV-5R, and its set to low power. I built a battery replacer with a 3A buck boost converter in it, so i can run an HT from my 100Ah lifep04 battery, and it actually is set a bit low, so the output is only 7.4vdc while not under load, so when i power the UV-5R from this buck boost converter, the RF output is a little lower than if i had the stock battery powering the radio, but even still, the radio eventually gets pretty hot during a ragchew. The buck converter is also getting pretty toasty as its only a cheapie 3A amazon one.
I figure i have 2 options if i want to keep using this UV-5R, either i find the mod somewhere (which i cant seem to find) to reduce the RF power output of the radio, or, i take the radio case off, mount some kind of improvised heatsink, and add a fan, then pray for the best and that it doesnt burn up lol.
Currently the radio is just sitting on the desk, not mounted in a housing or anything.
Does anyone have the specific details of bypassing the PA in the Baofeng UV-5R and connecting the antenna directly to the lower source of RF power before its amplified? Ive searched and cant find this mod anywhere.
73

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I have seen this MOD but for the Baofeng 888.

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I can only add if your are brave enough…

Find the schematic and locate the rf input pin to the power module and cut it and wire it to the antenna port. Should get you somewhere in the area of 20-80mw.
Enough for your house area.

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Honestly, the only people recommending customizing Baofeng 888s (or UV-* s) for ASL nodes are people who are looking for the absolute cheapest, rock-bottom builds or are looking to play around. Usually those builds are paired with modifying a cheap USB audio dongle which is problematic as well. There’s nothing wrong with doing that, especially if you want it for the learning/experimenting aspect. However if you want something reliable long-term, you either need to buy a radio module (HotSpot Radios, Clearnode, SHARI, etc.), use an SA818 module to custom-build a little radio harness, or just use an Masters Communications RA-25 with old mobile. If you can find it, a UHF mid-band Motorola Maxtrac/Radius can usully be picked up at any hamfest for < $30. Obviously this is assuming a US/CA residency. HSR and SHARI both offer a complete solution for < $100 with no headaches.

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I appreciate your reply, but honestly, im kinda tired of hearing that the solution to a problem is “just buy it”, instead of someone giving the instructions on how to actually modify something.

What happened to the spirit of ham radio? Who learns from just “buying” something ? Nobody.

While im aware that many hams are not that technically inclined, there are many that are technically inclined that enjoy the challenge of making and modifying ham radio equipment, (the way it used to be) and the simple fact is, that if you can do something yourself, why “pay” for someone else to do it?

I cant count the number of “build your own allstarlink node with a baofeng” videos ive encountered online, and “none” of them have ancountered an overheating uv-5r before?
I simply cant beleive that to be true, and that eventually all those people came to the conclusion that they should dump their project and buy a prebuilt SHARI node, or, just slap a fan on their uv-5r lol.

Someone out there must have the specific detailed plans to modify the RF to lower the output (and thus the heat) on one of these radios, i refuse to beleive im the only one who has to pioneer this proceedure lol.

If anyone knows the detailed procedure to bypass the PA on a UV-5R, and tap the output directly from the source for a lower RF output please feel free to post ot here, I’m sure im not the only one who would benefit from this information.
Im sure i could eventually figure it out, but who wants to reinvent the wheel if they dont have to.
73

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I think if you read what I said carefully, I specifically called out A) Use an SA818 module to build your own radio harness because it’s a better roughly-the-same-cost solution and B) modifying a Baofeng 888/UV* is a good learning experience if you really want that. Lots of times this is coupled with modifying a sound dongle. I’ve done both and far more besides.

But what is very often lost in the mix of “modify a Baofeng” projects is that A) the electronics involved are poor and B) change often in subtle ways that don’t work across untracked version to version changes of the hardware. Is it doable? Sure. But how much is your time worth vs. this project and other things you could be doing with your time. Do you want the joy or learning experience of building it? Go for it; I applaud and support that 100%. If it’s literally the only thing you can afford? Also, go for it! Get on the air! But if you are just trying to build a cheap hotspot out of a Baofeng purely for having a hotspot, it’s likely not the right path for the labor investment vs. value perspective for something you can purchase for a little over double the parts cost that “just works”.

I’d personally like to get a new version of what W6IPA put out there as the “PIRIM” board. I just need to find some time to sit down with KiCad and design one. I can’t find his files online nor an email address.

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There is an awful lot of chatter about how certain radios won’t work at anything over low power and this and that. My experience is just go ahead and try it and see if you’re happy with it. I actually have a thermal couple glued to an HT metal back of the case to measure the temperature and then have a fan turn on and off based on how warm it gets. Another build i didnt bother with the temp monitor and just stuck a heat sink on the case with a fan directly on the heatsink. That build is an rt-85 on high power and gets slightly warm to warm when keyed for more than a couple minutes. Havent smoked one yet. I think in general if you dont need the power turn them down (common sense anyway) but if you need more RF output youll need to deal with the heat somehow. There are cool brackets on eBay for some of the mobiles that make it easy. I did another build with a moto maxtrac set at 25w (40 w radio) with a temp sensor and have the temp window set to turn the fan on when its keyed for more than a minute or two. That works as well.

I think others have said to pull the final out, that will take care of the heat problem for sure, Ive never bothered as I prefer to have a little umpf to make it down the street.

73

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The G5REV guide to building an AllStar node shows the mod using a Baofeng 888s. My guess is that the Baofeng UV-5R will be similar. Basically the mod just involves removing the final PA transistor and then adding a short from the exciter to the antenna. Search for 'G5REV AllStar build' and you want episode #5.

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From AllScan - How To - Build a High-Quality Full-Duplex AllStar Node for Under $150 -

Power Supply

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A common misconception is that HTs cannot be used at high transmit duty-cycles because they will get too hot, even in the Low power setting. The heat generated by a final output transistor is roughly proportional to the square of the voltage across it minus the power radiated from the antenna. If the antenna has a sufficiently low SWR and the voltage across the transistor is set to a minimum voltage, the transistor will dissipate far less power than its design capacity. Thus in reality if an HT is run at a sufficiently low voltage it can transmit on High power all day and stay surprisingly cool.

Retevis RT85 HTs run great from as little as 3.5V, and at that low of a voltage put out only about 250mW. This can be very useful for nodes that only need a ~¼-mile of range, and the HT will then be extremely energy-efficient (drawing only ~250mA * 3.5V = <1 Watt of input power) and stay super-cool. Once the supply voltage is increased to 4V they then put out around 750mW in the Low power setting and 1.25W in the Med or High settings. At 5V, they put out ~ 1, 2 & 2.5 Watts (Low/Med/High), and at 7.5V ~ 1, 2-2.5 & 5-6 Watts. At 5V their current draw is ~ 0.7, 0.95 & 1 Amps (L/M/H). Therefore I generally recommend running RT85's on 5V, but if you need maximum possible range go with 7.5V, or if you don't need much range and want maximum energy efficiency go with 3.5V. The difference in power input and output between 5V and 7.5V is 5V×1A = 5W in for 2.5W out, vs. 7.5V×1.5A = 11.25W in for 5W out. Thus with a reasonably low SWR the output final will dissipate ~2.5W @ 5V vs. ~6.25W @ 7.5V - resulting in a ~60% reduction in heat dissipation when run on 5V rather than 7.5V.

A small 3.5V 1A, 5V 1.5A, or 7.5V 2A switch-mode power supply will easily accommodate 1 Rx HT and 1 Tx HT with plenty of margin (the Rx HT only needs ~100mA). A node Tx radio should generally be used on Low transmit power because of the high duty cycle, but higher power levels may be OK if the supply voltage does not exceed 7.5V. These power supplies are widely available for as little as $6. Be sure to test any power supply for RFI issues as just one poorly designed power supply could affect your HF and VHF noise levels.

AC adapters have come a long way, they used to have only a transformer, rectifier and small filter cap providing unregulated output with a lot of ripple that could easily cause 60Hz hum, but now have good regulation, are highly efficient and usually EMC certified. It's easy to find inexpensive DC power supplies (~$10) or step-down regulators (~$5) that have a variable regulator IC, filter capacitors, and terminal block connections. A ~1mF or larger filter cap can further reduce any power supply ripple/switching noise. HTs can be run on their included batteries but for a node that may be transmitting for long periods ie. during nets or long QSOs it's better to not constantly charge and discharge the battery or have the radio shut off. A 12V battery system could also be used, but HTs can very easily overheat if run on 12V (even if on the low power setting) thus a step-down regulator would be needed.

Because RT85's run great on 5V they can be powered from a USB power source. USB power from RPi's and MiniPCs tends to be very noisy, but the AllScan URI141 solves that issue with an internal ~0.25Ω–2.5mF RC filter and thereby achieves a ~55dB roundtrip audio SNR.

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