Is it safe to operate a VHF radio without an arial connected ?

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Boo2

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Is it safe to operate a VHF radio without an aerial connected ?

Hi,

Question as title : can anyone tell me if it safe to operate a VHF radio without an aerial connected ? Obviously I won't receive anything, but my RO4800 radio and remote mic arrived today and I'd like to have a play before taking it down to the boat. The manual doesn't mention it but I read warnings in my model airplane days about burning out the output stages by operating transmitter with no aerial attached and wondered if marine VHFs are similarly afflicted ?

Thanks,

Boo2
 
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I'm sure most manufacturers will claim that the output stage is protected against a disconnected antenna and you will probably get away with it, but not guaranteed. Put it on low power and the risk should be very small.

Make up a simple dummy load - the radio will be expecting a 50 ohm antenna and probably trainsmits 1W on low power. Maplins will sell you a 2W, 68 ohm metal film resistor (part number D68R) for 44p. It will not be a fantastic match - really should be carbon, but they are hard to find these days - keep the radio on low power and don't transmit for long and it should be enough to protect your output stage. Solder it across a PL259 plug and put it into the antenna socket.

You have not explained why you want to run the transmitter without an antenna. Knocking up a crude dummy load like that will not stop you transmitting at all - it's not screened - so don't go pressing the DSC button - you may still be received at close range and trigger an emergency search!
 
nigelmercier said:
Sorry, couldn't resist.

I not that nobody has picked up on the legal aspect of this: while it is possible that you can test the transmit function at home, you may not do so.
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I think you are at liberty to do so into a well shielded dummy load.
 
Sorry - didn't read your post carefully enough - you want to tinker with it at home - my answer stands - you are probably OK if you keep it on low power, but put together a crude dummy load to be on the safe side.

Please post back your impresions of the radio - I'm thinking of getting one of them as we kit out the new boat. I don't particularly want the built-in AIS, but it's a good price for a radio with full numeric keypad and wireless second station.
 
The RO4800 radio and remote mic have an intercom function. If you just want to test the remote mic the intercom function won't cause the main VHF transmitter to operate. You can also use the remote to change channel and listen without triggering the VHF transmitter.
 
maby said:
You have not explained why you want to run the transmitter without an antenna.
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I assume for the same reason I was thinking the same thing last month - new toy arrived and I want to turn it on and play with it :). Not intending to transmit, but worried about having an unguarded "destroy my radio" button to get pressed by mistake.

Pete
 
I think the chance of damaging modern vhfs by not having an antenna connected is very small.

I've often wondered how the damage occurs and it seems its due to the rf energy being reflected back into the transmitter power amplifier which results in a much larger voltage appearing across the transistors, damaging them. However rf power transistors are much more robust these days and the power supply often has protection circuity to limit over currents so in the case of marine vhf transceivers you would be unlucky if damage occurred if you accidentally press the ptt button.
 
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prv said:
I assume for the same reason I was thinking the same thing last month - new toy arrived and I want to turn it on and play with it :). Not intending to transmit, but worried about having an unguarded "destroy my radio" button to get pressed by mistake.

Pete
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lustyd said:
4460_DoNotPressTheBigRedButton_1.jpg
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:p

Some colleagues and I once had cause to design and build a mockup nuclear power station control room for use by schoolchildren. It was quite sophisticated, driven by half a dozen PICs and a PC running some custom simulation software and requiring six operators at "mission control" style consoles with knobs, sliders, buttons, 7-seg displays, led bar graphs, plus various things displayed on a big screen at the front of the room. They had to work together to keep the power generation tracking the demand curve (of course, nuke stations don't really do that, but it would be pretty dull to just sit there supplying the base load :) ).

Anyway, among all the knobs and buttons, for amusement purposes we added one that they specifically should not press. It was clearly labelled so - we dressed it up as being a lamp test mode for the panel, certainly not to be used during live operation. What it did was flash all the lights and make the bar graphs and 7-segs chase their tails, like a fruit machine when nobody's playing it. Naturally this made it impossible for the team to keep things running smoothly for the twenty seconds or so that it lasted (though we silently inhibited all the really bad emergencies for the duration) - after they'd figured out what had happened, the rest of the team would typically round on whoever had pressed the "do not touch" button, as angry (pre-recorded) "video calls" from the National Grid came in to complain how far off the curve they were. But inevitably, teenagers being teenagers, nearly every group pressed it several more times during their simulator session :)

Pete
 
I bought a Radio Ocean RO4800 last year and very pleased with it. Hooked up to my Garmin Gpsmap750. I was a bit nervous about it until I learnt it was actually Furuno.

However for some reason it stopped sending out the AIS data on the NMEA 0183 network so it had to go back under warranty. I would however recommend Force Four as their attitude to sorting this out was excellent.
 
What most posters seem to have missed out on is the substantial risk of operating a VHF without an aerial connected is that the Lizards will get in and infect the circuits.
 
Lakesailor said:
What most posters seem to have missed out on is the substantial risk of operating a VHF without an aerial connected is that the Lizards will get in and infect the circuits.
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Not if you give it a good dusting of bicarbonate of soda first. It's all about the unmeasurable acidity, you see.

Pete
 
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