Calling all VHF specialists!

[C-Val]

Hi Everyone

On my Christmas break I have been trying to sort out a VHF voltage drop.
I am using a standard horizon 1700 about 3 yrs old.

I had it on one boat with a 8' Galaxy Shakespeare -- it worked great. I moved it to another boat with a brand new 8 ft Classic Shakespeare (with a recently soldered pl 259 by me a newbie). Even connected directly to the battery I am getting a massive voltage drop (from 12.5 to 7 volts) with PTT. I changed batteries and still the massive drop

When I put it back to the first boat my voltage drop is so small (maybe .2)
Back to the new antenna connected directly to battery again and massive voltage drop. I tried an old radio I had on hand with the same results.
The only thing common is my new antenna

I checked the soldered end of new antenna for resistance between the outer jacket and center pin. It read "1" which I assume is no resistance.

Is there any way at all that a poorly soldered pl 259 could cause this?
If so I might have to go try a crimped. I watch Dr Bobs pics and tried to follow best I could- may it is not good enough

If you have any suggestions I am all ears. I am at a loss right now. I thought voltage drops could only occur from poor power feeds - not when connected to a good battery directly

thank you

David and Val

[MikeR]

It sounds like you have tried to rule this out but the symptom you describe is usually related to the 12v wiring. When you say "connected directly to the battery" I envision the radio sitting on top of or next to the battery with no switches or fuses between, and relatively short wires. But if what you really mean is that the radio is connected directly to the battery terminals instead of being connected to a switch or fuse panel, then you can still have a wiring issue somewhere between the radio and battery. Usually it's traced to a faulty inline fuse or fuse holder. Doesn't take much corrosion in these to make things start acting wonky. Is the inline fuse holder the same on both boats you are testing?

-Mike

[Robert H. Wilkinson]

[hardee]

Just want to confirm that you are talking (or reading), Volts DC, and not amps because the draw to go from standby(or listen) is .45 to 1.0 amps and to transmit it goes up to 5.0 to transmit it goes up to 1.0 or 5.0 depending on low or high transmit power.

I have watched my volt meter when going from transmit to receive and I'm sure it does not drop 5 volts, maybe 1/2 volt for the tx time and then back up to 12.8 or so.

I tend to agree that it may be either a wire corrosion factor or an undersized wire for the length of run. When you say it is connected directly to the battery, by how long a wire?

Oh, and I am not a VHF expert, but I have some experience using them and am a firm believer in having at least 2 working radios on board all the time.

Harvey
SleepyC

[C-Val]

I will do my test again today on my last day off, but just to clarify I carried the battery up to the helm and clamped the 12” wires that come out of the radio to the battery posts

There is a glass inline fuse that came with the radio there however

The weird thing is when I put the same radio back in the original boat on a different antenna I only get a .2 volt drop

I was just wondering if my first time solder job on the new antenna could be the source of voltage drop

Thanks for helping me think thru this

I will repeat my test today to confirm

[hardee]

If that first time solder job shorts out the ground and the positive side on that antenna, it will burn out the transmitter finals on the radio. When you put an ohm meter across the plug on the antenna, you should see the "zero" resistance or open. There should not be any connection between that shield and the core.

Harvey
SleepyC

[thataway]

There is a protection circuit in the output finals of the transistors in the radio, which will protect the circuit--and final output transistors. It is very possible that a dead sort in either the PL 259, the coax or antenna, will cause the shutdown--normally this does not act as a short--but it is possible that it does in this case. Thus dropping the voltage severely. This would normally blow the fuse--so you do need to re-evaluate that. I usually pull the fuse out of the circuit--and use one on the fuse block--see below.

I would try with an "emergency antenna, or other antenna, before going any further.

All of the other comments are good and very valid suggestions, and where you have both looked and pretty well ruled out by putting the radio directly on the battery.

Also I find that most C Dory's do not have adequate wiring from the batteries to helm--and I either double the wiring--(add an extra #10 or #8 wire for the positive and ground to the electronics section. (I also often another or large fuse block--go from 6 to 12 fuses).

[gstraub]

Almost certain this is a problem with the DC wiring...a corroded connection, corroded fuse holder, too small a diameter wire for the length of the run, etc. I occasionally do radiotelephone safety inspections for commercial vessels and this is not at all unusual in an older installation. If you did a lousy job soldering the antenna connector, as others have noted, the radio would likely roll back power so that it did not damage the output circuitry. In that case, since the radio would not be transmitting at high power, there would be little current draw increase over receive and hence no real voltage drop. So, I agree with those that say the issue is likely with the DC wiring. I'm not saying there isn't another problem, or that the antenna connector is not an issue, but I would start with a look at the DC wiring.

Gerhard
PS. I've chased my tail for hours on one of these, so don't give up!

[thataway]

[smckean (Tosca)]

Frankly, I'm a bit puzzled by your description of the problem; that is, a "voltage drop". Voltage drop is usually measured in a static situation (i.e., when no load current is flowing). If the VHF is turned on, then like all loads, the entire voltage potential "drops" across the load. A partial drop in a live circuit doesn't mean anything unless there are multiple loads in series and you are measuring btwn the loads.

Where exactly are you measuring this "voltage drop" and is the radio turned on or off when you measure it.

P.S. If you are measuring across the battery terminals with load current flowing and see a voltage drop, that has to do with the internal resistance of the battery not with the load.

[thataway]

[C-Val]

Hi Everyone
Thank you for all you insights into my vhf voltage drop problem

Just to clarify, I have a fully charged spare battery I brought up to the helm.
I dismounted the SH 1700 and set it virtually on top of the battery with the short wires from radio connected directly to battery posts. (there is an inline fuse on power) Voltage is measured right from battery posts.

I have access to two boats. When I do this on the first boat connected to its antenna voltage drops only about .3 volts when I key the mic. (This is a Galaxy 5225-xp higher quality antenna)

When I carry the radio and battery to the second boat with a new 5101 Shakespeare entry level antenna (with my solder job), voltage drops from 12.5 down to about 7 volts when I key the mic on 25 watt.

According to the shakespeare antenna manual there should be no continuity between the centre pin and the outer ring. When I checked my 5101 antenna there was no continuity so I assumed I did good job.

After much research and reading your posts, my only conclusion is something I read on another boating website. It states

"If there is a bad connection in the coax or the antenna, too much power is reflected back to the radio and the radio itself will begin to power itself down to protect itself"

I wish I had a vswr meter but I don't. I contacted the local ham radio club here and they invited me to attend their meeting tomorrow. I will let you know how it goes.

I think they want me to join the club and get my ham radio license for marine!

This has all been a bit discouraging for me as I wanted to use the boat over Christmas. The upside is I will pretty soon be a radio tech myself!

thanks again

David

[colbysmith]

David, it seems to me that if the antenna is making the difference, the antenna is the problem! (Or the antenna's connection to the radio.) Or am I missing something more in your posts? It could be a bad antenna or a bad connection. The easiest thing to do would be go to Radio Shack and buy a new connector, one that is solderless. Install it and see if the problem is solved. It could also be in the antenna cable as well. But again, the easiest thing to start out with would be remove and replace that connector. (Actually, check your cable first to make sure it's not pinched anywhere, and is connected properly at the antenna.) Colby

[C-Val]

I totally agree!

thanks

[smckean (Tosca)]

I'd like to correct one thing I said above.

"Voltage drop is usually measured in a static situation (i.e., when no load current is flowing)."

As stated, this is wrong. I chose the words poorly. Voltage everywhere in a circuit is the same if no current is flowing. Voltage drops occur when a current flows thru a resistance; so having a current flow is necessary for a voltage drop to occur. What I meant to say is that if you are measuring a voltage drop when no load current is flowing (i.e., the load is turned off), and you measure a voltage less than what you measure at the source, then there is high resistance somewhere btwn you and the source (e.g., corroded junctions, too long a run with too small a diameter of wire, etc).

I regret the use of the word "static" because there really is no such thing. In order to measure the voltage, you need some sort of voltmeter. All voltmeters draw a tiny amount of current across a high resistance....that's how it measures the voltage via the V = IR law, where I is the amps flowing thru the meter, R is the resistance inside the meter circuit, and the calculated V is the voltage the meter is calibrated to report. So when you measure the voltage btwn 2 points in a circuit that is "turned off", a tiny amount of current is flowing in that circuit assuming there is a source connected. Note that a voltmeter doesn't really measure voltage, but rather it measures this tiny current passing thru the meter.

Another way to say this is that while you are measuring the voltage in a circuit where all loads are turned off, there is still one load that is on....namely, the voltmeter itself.