What is the true duty cycle of a portable radio?

BlueDevil · Oct 31, 2018

What is the true duty cycle of a commercial or professional grade portable radio? I have seen a lot of people refer to the 5/5/90 (TX/RX/Standby) used to determine the battery life as the duty cycle as well. Is this accurate? Is it a weighted average? I know A LOT of people that have their portable radio keyed up for MUCH more than 5sec at a time.

What say you?

alcahuete · Oct 31, 2018

BlueDevil said:
I know A LOT of people that have their portable radio keyed up for MUCH more than 5sec at a time.

It doesn't refer to seconds, so 5 seconds has nothing to do with it. It refers to a percentage. So 5% spent transmitting, 5% spent receiving, and 90% of the time in standby.

So in a 8 hour shift, for example, the radio would spend 24 minutes transmitting, 24 minutes receiving, and 432 minutes standing by.

BlueDevil · Oct 31, 2018

alcahuete said:
It doesn't refer to seconds, so 5 seconds has nothing to do with it. It refers to a percentage. So 5% spent transmitting, 5% spent receiving, and 90% of the time in standby.

So in a 8 hour shift, for example, the radio would spend 24 minutes transmitting, 24 minutes receiving, and 432 minutes standing by.

So a portable radio can tolerate transmitting continuously for 24 minutes?

alcahuete · Oct 31, 2018

BlueDevil said:
So a portable radio can tolerate transmitting continuously for 24 minutes?

No idea if the radio components themselves can, as the duty cycle does not refer to the radio itself. The duty cycle refers to the battery, and the length of time the battery will last between charges using a 5-5-90 cycle.

If a battery is 5-5-90 rated for 8 hours between charges, if you go 10-10-80, for example, the battery is not going to last 8 hours. If you go 25-25-50, it's not going to last for 8 hours.

That's all the duty cycle is referring to.

BlueDevil · Oct 31, 2018

alcahuete said:
No idea if the radio components themselves can, as the duty cycle does not refer to the radio itself. The duty cycle refers to the battery, and the length of time the battery will last between charges using a 5-5-90 cycle.

If a battery is 5-5-90 rated for 8 hours between charges, if you go 10-10-80, for example, the battery is not going to last 8 hours. If you go 25-25-50, it's not going to last for 8 hours.

That's all the duty cycle is referring to.

So if a radio does not have a battery then it does not have a duty cycle?

alcahuete · Oct 31, 2018

BlueDevil said:
So if a radio does not have a battery then it does not have a duty cycle?

They do. Not all radios are designed to transmit 100% of the time. Most commercial repeaters will have a 100% duty cycle. Some amateur repeaters will have a 50% duty cycle, etc. Some will even have different duty cycles based on different power levels. Some manufacturers will list it, some don't.

But we're talking about completely different things here. The 5-5-90 almost always refers to the battery.

FluxMux · Oct 31, 2018

It depends on your radio

Duty cycles in terms of tx outputs are ratings based on the transmitters, and usually that duty cycle should have a time window allotted to it. So if you had a max transmit time of 2 minutes on your portable with a 50% duty cycle, you should not be transmitting for another 2 minutes. You should be able to receive all day long with any radio unless you've overdriven your speaker circuit. RX and standby are the same thing unless you are squelching everything out for 90% of the time. hehe.

The duty cycle you are referring to is referring to your battery usage, and you could use the mAH rating of the battery (if you knew how much draw you were creating on tx and rx) to determine how much talking, listening, or just having it able to receive it can do before the battery needs replaced/recharged.

BlueDevil · Oct 31, 2018

FluxMux said:
So if you had a max transmit time of 2 minutes on your portable with a 50% duty cycle, you should not be transmitting for another 2 minutes.

Understood. We are on the same page. What is the actual duty cycle of a portable radio? 50%?

KK2DOG · Oct 31, 2018

Icoms have always been advertised as being 100% duty cycle.

FluxMux · Oct 31, 2018

BlueDevil said:
Understood. We are on the same page. What is the actual duty cycle of a portable radio? 50%?

Your radio would stipulate this. Every transmitter's final is different. If the radio is well designed and can shed the heat well enough, you could talk all day. If not, it should tell you as much and give you the max time you should be transmitting and how much down time before you key the mic again.

Barring having that information, the rule of thumb (literally) would be if you notice the sucker getting really hot, get off the mic and give it down time to cool off. Another way of knowing you are pushing its limits is the person on the other end telling you that your signal is starting to suffer.

BlueDevil · Oct 31, 2018

I will have to look through some of my manuals a little more closely to see what it says about duty cycle. I get the "rule of thumb" as it pertains to heat. I figured that there might be a kind of general catch all duty cycle % for all portable radios.

alcahuete · Nov 1, 2018

It's impossible to have a catch all, because not every radio is designed the same.

zz0468 · Nov 1, 2018

BlueDevil said:
I figured that there might be a kind of general catch all duty cycle % for all portable radios.

No. Portable radio features vary by make and model, as do the specifications. Transmitter duty cycle will vary widely. It's frequently not even specified in portable radios, as typical commercial or public safety use doesn't come anywhere near 100%.

speedway_navigator · Nov 1, 2018

I bet the RX duty cycle is close to 50% in major cities during day and evening shifts.

A trunked radio version of standby is not the same as a conventional radio, the trunked radio is always receiving, it only opens the speaker when the proper talk group is on. I don't know if there is a formal definition of standby.

A portable does not have the ability to dissipate heat like a mobile or repeater. I don't know for a fact but I expect radios have a thermal limit switch to turn off the xmtr when it gets too hot.

kayn1n32008 · Nov 1, 2018

BlueDevil said:
So a portable radio can tolerate transmitting continuously for 24 minutes?

The 5/5/90 is only for establishing an average battery life based on current draw in various states and is directly related to a battery capacity. It has nothing to do with transmitter duty cycle.

Sent from my iPhone using Tapatalk

kayn1n32008 · Nov 1, 2018

BlueDevil said:
Understood. We are on the same page. What is the actual duty cycle of a portable radio? 50%?

Doubtful. For any brand portable. It is probably more like 10-25%.

Sent from my iPhone using Tapatalk

MTS2000des · Nov 2, 2018

The ability of the portable transmitter to withstand long keydowns is limited to the cooling of the power amplifier. Most portables have limited heat sinks, usually the rear chassis and most of the time it's covered by a battery pack.

Two things here: poor heat dissipation due to a battery being in the way (unless the radio has a bottom mount battery with the rear chassis unobstructed) and of course, the effects of the heat on the battery itself, which usually shortens the life of the battery while reducing output capacity.

Bottom line is portable radios are designed for intermittent transmit of the typical LMR user, less than 30-60 seconds of keydown, followed by several minutes of receive which allows the unit to maintain a lower operating temperature.

Most hams usually function complete opposite, the PTT is not a "Push to Talk" but utilized as an RTL "Release to Listen" and then wonder why their portable batteries don't last and the radios finals die an early death.

RadioGuy7268 · Nov 2, 2018

As mentioned, heat is the enemy. You've got to be able to dissipate the heat, and power generates heat.

I once had a situation where we needed to busy out the FB8 Home channel of an LTR system & force units to trunk off onto other channels. We rigged up a P1225 LS portable with a battery eliminator, set the power to 1.5 watts, turned off the Time out Timer, hooked it up to an outside Yagi, and dead keyed the portable for 48 hours straight.

I doubt it would have done it set at 4 watts, but it handled low power like a champ, and I still have that P1225 radio in service - almost 20 years later. How's that for duty cycle?

needairtime · Nov 2, 2018

LOL RTL...I guess there are some motor mouths out there...

Anyway yeah it depends on the manufacturer and particular radio. I noticed on my Kenwood TR-2500 that Kenwood actually rated its battery life based on 1 minute transmit, 3 minute listen, which would be 25% duty cycle. I think they also had squelch broken during the receive time.

On my TK-810 LMRS, another Kenwood, they rate it for 100% receive duty cycle and transmit only 20% -- less than the TR-2500 HT.

I was looking at some of Kenwood's repeaters and I think the TKR-820 only has a 50% duty cycle transmission. Note that they rated in percentages, so these must be an average over many hours.

Then there's the guy in the CB thread that taped his CB PTT down for 12 hours with the antenna disconnected...and it still works!

This definitely does not apply to all radios. In fact I suspect most non-repeaters the duty cycle typically is well less than 50%.

BlueDevil · Nov 2, 2018

To clarify, my reference to the 5/5/90 was an example of what I have seen other people use to determine the transmit duty cycle. I was already well aware that this formula was used specifically for estimated battery life.

My intended discussion (which many of you have addressed) was related to the duty cycle of the transmitter. I completely understand that there are many different variables in determining a duty cycle heat dissipation being a big contributing factor. Waiting for the radio to start feeling warm while in your hand seems like that might be a little too late.

I guess I was looking for a more generalized estimate of the transmitter duty cycle of commercial or professional grade portable radios. It safe to say that generally most commercial and/or professional grade portable radios, ceteris paribus, have at least a ___% (i.e. 20%, 25%, 50%, etc.) duty cycle?

What is the true duty cycle of a portable radio?

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