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ContinuousWave: Small Boat Electrical
VHF radio problem
|Author||Topic: VHF radio problem|
posted 09-21-2008 08:36 PM ET (US)
I have a Standard-Horizon Eclipse that is receiving perfectly both weather channels and transmissions from a handheld, but it is not transmitting. When the mic is keyed, the TX lamp lights on the display, however no transmission. I have tried the test with a coax connector wired to a 40-watt light bulb, but the bulb does not glow when mic is keyed ( the test checks positive on a Standard MC535 backup radio ).
Are there any things I can try at home - or am I headed for a repair shop ? Any ideas will be greatly appreciated !
posted 09-22-2008 12:41 AM ET (US)
Tune two radios to the same channel. Turn the squelch on
the other radio until it makes white noise. Key the Eclipse.
Does the other radio go silent? If not, the Eclipse is not
Standard-Horizon has pretty good customer service, with a
posted 09-22-2008 02:38 PM ET (US)
Thanks Chuck ..... I'll try that !
posted 09-23-2008 09:30 AM ET (US)
Using an incandescent lamp as a dummy load
When I was a boy I used to see my father using an incandescent lamp as a dummy load for his amateur radio transmitter. In the 1960's transmitters used vacuum tubes and had adjustable tuning networks.
According to Ohm's Law:
I = E/R and P =IE
P = E^2/R and R = E^2/P
So we can compute the resistance of an incandescent lamp of a particular wattage and voltage. A 40-Watt lamp as mentioned above would have a resistance of
R = 117^2/40 (E=117, the nominal "120" voltage of most utilities)
R = 13689/40
R = 342 Ohms
That would be its hot resistance, and as we know, incandescent lamps act like negative resistances, that is, the more voltage placed across them the higher their resistance becomes as the lamp filament heats up. When cold the filament of a 40-Watt has less than 342-ohm resistance.
Measurement of a 60-Watt lamp (as I didn't have a 40-Watt available) showed that its resistance was 17-ohms when cold.
It seems reasonable that a 40-Watt lamp would have a higher cold resistance, so we could approximate it as 25-ohm (based on the inverse relationship between wattage and resistance seen in the 60-Watt lamp).
As a dummy load a 40-Watt incandescent lamp would be fairly decent for a radio transmitter expecting a 50-Ohm load. With only 25-Watts of power applied to it, the filament would never be heated to the final resistance of 342-Ohms, so it might end up somewhere between 50- and 100-Ohms with a nice soft glow in the bulb.
posted 09-23-2008 10:31 AM ET (US)
Had a similar problem with my radio. Receiving and transmitting but no voice. Buddy of mine suggested checking the mic; took it apart, sprayed contact cleaner and whola! Works like new. Just a suggestion. Hope it is this and not something more expensive. Love those $10 fixes!
posted 09-23-2008 07:48 PM ET (US)
Diver Dan--I do not think your assessment that the problem with JB's transmitter will be found in the microphone is likely to be accurate. In your case, your transmitter was operating but lacked modulation. In JB's case, his transmitter appears to not be generating any radio-frequency output.
The notice that the TX light is illuminated when the PTT button is pressed indicates that the microphone is initiating the transition to TRANSMIT mode. The lack of any indication of radio-frequency output by the incandescent lamp dummy load indicates the transmitter is not operating properly.
posted 09-28-2008 09:51 PM ET (US)
Thanks for the responses. Standard quotes a $65 flat-rate charge for any repair required to make the radio functional, However that charge coupled with shipping both ways makes purchasing a new radio (which I have done) the best option for me. Having said that, I would still like to attempt a repair. Here is the current situation:
The Standard-Horizon Eclipse receives weather and other channel transmissions, silences the static on a handheld located within 100-feet with squelch setting at lowest theshold when the mic is keyed, does not cause any illumination during the 40 watt bulb test when the mic is keyed .
Uniden 535 receives as noted above, also silences the squelch on the handheld, lights the 40-watt bulb when the mic is keyed. Does not send a receivable voice or any other type of noticable transmission when mic is keyed.
Initially both radios were tested with an old Shakespeare 'shorty' SS whip equipped with a new 6' length of coax and two new soldered on connnectors. Subsequently a new antenna was tested on both radios with the same results. Power supply is not suspect.
Thanks JimH for your input ..... but, my knowledge of electronics is minimal. Please tell me if I am wasting mine and everyone else's time hoping to track down a 'home remedy' for these radios.
posted 09-28-2008 11:02 PM ET (US)
Take the radios apart. Give them a very close visual inspection. Many electronic problems reveal themselves visually.
posted 09-28-2008 11:54 PM ET (US)
Note that VHF radios are supposed to be repaired by someone
with an appropriate FCC license.
It's strange that the radio passes the squelch test (it's
First: check that the radio hasn't been set to 1 W mode. If
After that, I'd open things up (start with the mike, that's
One option is to turn the Eclipse into a "listen to the boaters
posted 09-29-2008 01:37 PM ET (US)
Thanks Chuck ..... I've purchased some electronics cleaning spray and will open up the case for a look see.
I think all of the tests were done on 25w power ... but since you mention it, I'll re-test and be certain I was not on 1w.
If the PL259 solder connections are not PERFECT, could they cause the problem ? Now I am second guessing those as well, even though I have always been able to attach them with no problem in the past.
posted 09-29-2008 06:45 PM ET (US)
Chuck raises a good point: it is illegal for non-licensed personnel to perform service or repairs on VHF Marine Band transmitters. There should be a notice of this in the transmitters owner's manual.
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