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Go Back   SailNet Community > On Board > Gear & Maintenance > Electronics > VHF Output
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Thread: VHF Output Reply to Thread
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Topic Review (Newest First)
10-25-2012 09:49 PM
tibtib
Re: VHF Output

There may be a problem with the cable that you are using between the radio and your antenna meter. I suggest that you try another jumper cable. If the reading is still low, you should consider the possibility that your meter is not working properly. Borrow another meter from someone and compare readings.
10-25-2012 12:37 PM
asdf38
Re: VHF Output

Hello,

You're making a number of generalizations which aren't accurate.

Whether or not the VHF has regulation is not in question. The microcontroller driving the menu, the screen, backlights, audio amplifier for speaker, beeper for registering button presses the serial interface to external GPS's, the flash memory for storing settings etc. etc....these internal devices all require various regulators to create whatever voltage(s) they each require - probably linear because they're low power but perhaps one or more bucks to knock down the bulk of the voltage more efficiently. The only question, because I don't have the analog/amplifier or VHF radio experience say with certainty is how would the amplifier react.

As for mass market devices well those cheap compact Apple imitation square AC USB chargers use high frequency switching supplies for a few bucks. This dual usb car charger is $5.54 putting out 2A@5V and certainly isn't using a linear regulator which would mean 2A@12V in for a loss of 14+ watts - not in that small package (I have this in my boat). So you're completely underestimating the prevalence and low cost of various regulators, as well as their outright necessity for modern low voltage electronics.

For example something like the victron battery monitor won't have anything that internally runs on 12V. It's all regulated down. This generally applies to other marine instruments. For what it's worth I've designed 50A shunt sensing 12V current measurement circuits.

Again, we're largely wasting everyone's time with this debate except for the small area where this stuff intersects debugging marine equipment. The point to what I'm saying is that with modern digital based equipment, input voltage issues are farther down on the priority list of debug than they might have been in the past. Not to mention the fact you keep glossing over which is that all these radios are specified to operate between 10V and 15V - if 10+V is getting to the VHF when transmitting at full power that's in spec (if and only if it's 10+ volts WHILE transmitting and drawing full power). The next logical debug step is to look elsewhere. Of course starting the engine to raise the input voltage is low hanging fruit and I don't discourage it.

The fact that two entirely different radios measure the same (how close was it actually?) output power calls the tester in question more than anything else. It's kind of like measuring two cars maxing out at 35Mph with the same speed gun and concluding the gas is bad. Two different radios would have significantly different reactions to low voltage/high resistance input power which makes seeing the same output power pretty unlikely.

Edit: This picture actually shows the IC and inductor for the internal 10W buck conveter (DC-DC) of this $5 usb car charger.


Amazon.com: Griffin Powerjolt Dual Universal USB Micro Colors May Vary: MP3 Players & Accessories Amazon.com: Griffin Powerjolt Dual Universal USB Micro Colors May Vary: MP3 Players & Accessories


10-25-2012 12:23 AM
hellosailor
Re: VHF Output

"Buck converters (step-down), boost converters (step-up) and buck/boost converters (anything to anything) aren't special. They're in almost every electronic device over a few watts.... on the oder of $15 in lowish quantities."
Actually, not. First of all, dcd-dc converters of any type are not used in anything like a mass or majority of consumer electronics. Bulk regulators, when needed. But anything more? No, not without a real need. You go add $15 worth of components, or even $5 worth of components, to a VHF that is designed to sell for $100-150. You'll bump the retail price by $20-30 and lose market share, that's the reality of the mass market. If you can knock one buck, one dime, off each board? That's sometimes the difference between success and bankruptcy. That's just the way it is. And there are engineers who are hired specifically to say "OK, we've got this, what can we knock out of it?" including electronic components.
What you would like, has been proven impossible in the mass market. In a $500 VHF, sure, you could expect that. And we could all buy bespoke suits instead of khakis. Ain't gonna happen.

"A cheap incandescent flashlight won't have regulation but a good LED one will." Not really. Many LED flashlights have no regulation, they rely on the battery voltage being the limit and don't regulate anything. SOME use upconverters, in order to get a 4.5V white LED running off a single AA cell, but that's because it has to be done that way--not because someone wanted to spend the money doing it. Others use *power* regulators, simply because using a power regulator on a $10 prime LED can double the operating life, and some folks will pay for that. Again, it is not mass market. Like a Bose stereo, they ay sell a lot of them, but it is not mass market.

"but being able to put out 25W on your VHF at 11.5V in a boat is a pretty damn good reason for regulation. " Not really. If all you can supply is 11.5 volts, the "operator" has already failed to maintain their nominal power supply. That's user error, failure, and not common operating mode. In order to make that happen with an ordinary regulator, you'd have to design the whole radio to work at 10.5v,not 11.5, then add a regulator which only had a one-volt power drop in it. Oh yes, all regulators consume power and further reduce source voltage, until you get into dc-dc converters and then again you drive the costs up AND you create RFI in the radio itself, which makes a bad thing even worse.

You think you can do a DC-DC regulator to make your VHF happy with 11.5 volts for under $15? Great, wire it up, hook it on! But the industry has good reasons for not doing it, starting with that HUGE $15 extra cost, from their point of view.

Sure, there are all sorts of new poewr supply chips on the market now. They still cost money. They still need engineering expenses. They still need HEAT SINKS which means more space and more money again. You're not going to do the job with a 2mm x 2mm chip.

And coming back to the most important point of all: 99% of the buyers have no need for it, no understanding or appreciation for it, and no budget for it. Did I mention, "Ain't gonna happen." ?

For those buyers who want better emergency operation, buying a $20 dedicated VHF battery and mounting it behind the radio will do very nicely. It will buy you more protection that any regulation of the vulnerable ship's power system.

But coming back full circle, if you've tested two radios and both put out the (curiously same) 15W of power...I'd look to what you are feeding them. Especially since both are being degraded to the same power level, indicating that's all the power they can find on the DC line. tell me how easy it is to improve the electronics--when the way simpler problem of wiring is still apparently in the way?

First fix it. Then worry about whether it needs to be improved.
10-24-2012 11:57 PM
asdf38
Re: VHF Output

Hello,

Buck converters (step-down), boost converters (step-up) and buck/boost converters (anything to anything) aren't special. They're in almost every electronic device over a few watts. Not just because of efficiency but because efficiency means less heat and thus smaller size (dissipating heat takes size). I've designed them and specified them and a 5W fully integrated (mosfet/inductor included) buck starts at a couple bucks in low quantities. A 25-50W converter, non-isolated, fully integrated is on the oder of $15 in lowish quantities.

As a neat aside there is a simple device called a Hydraulic ram that can literally move water upwards and is exactly analogous to a step-up DC-DC boost converter.

A cheap incandescent flashlight won't have regulation but a good LED one will. Sure if there is no reason for regulation there will be no regulation but being able to put out 25W on your VHF at 11.5V in a boat is a pretty damn good reason for regulation.

An MPPT controller is a buck/boost or perhaps a more exotic topology or variant, marinized and controlled by a microcontroller with a special charge algorithm. The expense results from the standard combination of ruggedization and low quantity production and perhaps an emphasis on efficiency adds a bit more cost. But the power conversion involved, variable dc-dc by itself isn't especially expensive. This is why it's so common.

If the lawyers really looked over the manual AND the performance does significantly degrade while still within the stated operating range of 9.5-15.8V THEN there would be a problem. Hence why I still suspect it's unlikely.

Note, all this stuff I'm talking about has come down in price significantly over the years along with everything else computer related. Power supply design used to mean discrete op-amps and lots of other chips. Now IC's 2x2mm include all the control circuitry for 50W+ supplies and their higher frequencies cut down the size of the inductors, capacitors or transformers needed. So perhaps in years past nothing I'm saying now applied.

Back to the thread I do agree that checking the voltage is a good idea. Certainly outside the stated operating range all bets are off. But if I saw 10 or 11V while transmitting at full power I'd look elsewhere for the problem. Hence why I asked why you thought otherwise.
10-24-2012 11:09 PM
hellosailor
Re: VHF Output

"obviously you can get any amount of power from any voltage or convert one voltage to another if needed." No, you can't. There are separate limits on voltage and current, depending on source and other physical limits (like wire size and length). While you can convert voltage to current and vice versa, you need special equipment to do that with DC circuits, or transformers to do it on AC. Since we're talking about DC here, the answer is that you can't convert voltage to current, or vice versa, without considerable extra expense. Think of what an MPPT solar controller costs--that's active conversion.

"Nothing is stopping them at the least from throwing a DC-DC on the front end."
Wanna add even 1/4 of that MPPT cost to your average VHF radio?

"Also it's unlikely for circuits to run off external voltages directly." Unlikely only if you don't know about electronics. While some circuits are regulated, there is no reason to internally regulate devices that are powered from a specific and limited DC power source. Got a flashlight that uses 2 D cells? No need to regulate it, you KNOW it is running off 3VDC maximum and the amperage doesn't matter, the bulb will self-limit that.

Same thing for a DC car stereo or a VHF radio. Regulators cost money AND consume power AND take up space in the product AND add to warranty costs because anything can and will fail in some percent. Vendors know--for a fact--that a "12VDC" system is going to be regulated to a maximum of 14.4 volts, by industry convention. And that a dead battery will limit the lower end to about 12 volts at any effective power draw. So there's no need to regulate the equipment, because your alternator already is regulating it. Yes, that regulator can fail too and when it does, it is expected that everything running off it will have failures.

So the way these things are done? Unregulated, and that's plenty good enough. Your problem has got nothing to do with regulation or power conversion, you've probably got a simple problem of old cheap wiring, or wiring that was botched. And those problems can kill any electronics, no matter how many redundant layers of "protection" you add onto them.

"This ...doesn't suggest by itself that output power would go down at lower voltages. " You're reading a CONSUMER manual designed to help you operate the radio, not an engineering course. Odds are there's a section up front from the lawyers, telling you not to operate it in a bathtub or the rain, but very little about what lightning and alternator failures and other issues can do to the radio. And they've got no reason at all to confuse you with technical graphs showing how the circuits degrade once you go outside the operating parameters. Moisture? Temperature? Dew point? They'll all affect operations, just like high or low voltage will. See the graph anyplace that tells you how much they'll affect it? Or even operating limits?
And do you think anyone wants to scare the customer by confusing them with numbers, like, "This product will suffer an additional 10% total harmonic distortion when operated on 11.9 volts, and 20% harmonic distortion plus blah blah intermodulation and frequency splatter at 11.5 volts..."

Oh yeah, that would help everyone.

If you want technical information, look to technical sources, not a consumer manual. Look to technical radio reviews. The ARRL has them for members, for ham radios, and they're very explicit about these issues. For marine radios...damfino who does lab reviews of them.
10-24-2012 10:50 PM
asdf38
Re: VHF Output

Ok. Just piques my curiosity because obviously you can get any amount of power from any voltage or convert one voltage to another if needed. Nothing is stopping them at the least from throwing a DC-DC on the front end. Also it's unlikely for circuits to run off external voltages directly. Except for special cases most chips run from 5V or lower (usually 3.3V, 1.8V, 1.2V or less) so all electronics in a 12V application have some form of regulation that usually leaves them immune from reasonable changes on the input. That said I know little about VHF amplifiers specifically and their voltage needs.

I just skimmed the manual for one random radio (UM380) and it does repeatedly cite 13.8V, but it's done in the context of specifying current. I.E. 6A @ 13.8V when transmitting at 25W. This implies current might vary based on voltage but doesn't suggest by itself that output power would go down at lower voltages. Anyway, fairly minor detail.
10-24-2012 07:55 PM
hellosailor
Re: VHF Output

"How come you're assuming this?"
From comments and instructions from various radio manufacturers, and observing the operations (including power output) of various transmitters operating at reduced voltage or restricted amperage.
In order to get power out, you need power in. The amount of amplification is fixed, so if there's not "enough" power in, you'll get less power out. Often stated in transmitter specs, where they'll say the rig is designed for 13.8 volts (typical "12" volt radios) or in the case of very good equipment, it may actually be rated for full power at 12 volts or less.
And fwiw, at 9 volts, or even 11 volts, you can expect significant distortion and other problems, not just a weak signal.

We had an old VHF that was refusing to transmit. I figured, old transmit button, something's worn out, fix the button. Autopsied the button, couldn't find any problem. DID find a punked out fuse connection--and that's all it took to stop the radio from transmitting completely.
10-24-2012 07:07 PM
asdf38
Re: VHF Output

Quote:
Originally Posted by hellosailor View Post
Radio might not be getting a full 14.4 volts, engine power. At battery power it will have a lower output. Check again with the engine running, and see what voltage is making it to the radio itself.
How come you're assuming this? Is it something common with VHF's? I would have assumed that any decent piece of marine electronics can handle the full range of inputs (roughly 9-15V) without degraded performance.

Edit: Nevermind, I assume you were using this?
http://shakespeare-marine.com/access...menupick=art-3
10-24-2012 03:52 PM
hellosailor
Re: VHF Output

If two different radios each showed as 15W when connected to the same power line, that would indicate you are not getting enough power to the radio. Could be undersize wire too long, could be crud at connections, could be other issues but wiring sounds like #1.

Try getting a 20-30W light bulb, a cheap incandescent bulb, and hooking it up where the radio goes. Use a dmm to check voltage and amperage, because "filament" bulbs are self-limiting and if it says 25W on the bulb, it will damned well draw 25W from the lines if that is available. If you don't see it drawing that much power, you have a supply problem.
10-24-2012 02:02 PM
beanctr56
Re: VHF Output

Thanks all, I guess I should test the radio with the engine running although I keep the boat plugged into the dock so I should have full power. I also tested another spare radio and it showed 15w. I'm just hoping that something else is not damaged that I overlooked. If my antenna cable was damaged would the tester show a good antenna? Rick
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