VHF Antenna Splitter Breakdown?

Jul 1, 2009
221
Catalina 310 Sydney-Pittwater
Recently I noticed that the AM/FM Radio lit up and the speakers made a noise whenever I pressed the send button on the VHF Mic, even though the radio was turned off , including at the fuse switch.

As disconnecting the FM aerial from the splitter stopped this problem, I replaced the splitter. The problem appeared solved. However, 1 week later I am having the same problem.

Also, when transmitting with the FM radio on, the sound of the latter is severely disrupted.

Do splitters breakdown and, could this problem damage any of the radios?

I do not really want to connect the FM to another aerial, as I think I need the mast height for reasonable reception in our area.
 
Dec 4, 2013
22
Hunter 27 Lavilla Cove Marina
If your splitter connects the vhf antenna to your marine radio and your FM broadcast radio then that's is not good. Your vhf marine radio does not see a matched load and therefore greatly reduces its effect and reduces range. What you are doing is pumping 25 watts of power into a radio designed for microvolts of signal even considering the splitter losses. Good communications protocol dictates a single lead from antenna to radio transmitter thus providing a matched 50 ohm load resulting in maximum transmitted power delivered to the antenna.
 
Sep 25, 2008
7,077
Alden 50 Sarasota, Florida
Splitters break down all the time. That's why they should never be used under any circumstance.
 
Jan 22, 2008
423
Catalina 30 Mandeville, La.
Are you able to test the antenna? You may have a poor match and the high reflection may be why you're seeing more interference. Any connectors that look bad, probably are, and almost certainly any that aren't weatherproofed.
 
Feb 17, 2006
5,274
Lancer 27PS MCB Camp Pendleton KF6BL
Most COTS (commercial off the shelf) splitters are passive in nature. They are designed to split a source between two or more loads. Most of these are simple circuits with resistors and are designed to match a specific impedance. These passive splitters can go bad and often do.

Amplified splitters have an amplifier built into the system. They are very broadband and will amplify EVERYTHING that passes through them. These are referred to as active splitters and require DC voltage to work. A loss of DC means very high attenuation or impedance mismatch.

RF splitters are different in design. They are specific in frequency and power ratings. Some are broadband (DC to 2 GHz for example) or some are narrowband (70 MHz bandwidth for example). [Note: FM broadcast radio is 20 MHz in bandwidth from 88 MHz to 108 MHz] They are usually tuned with inductors and capacitors to act as filters either high pass or low pass. Good designed splitters (Mini Circuits for example) have high impedance return paths, basically blocking any leakage from one path to the other.They will go bad if too much power is inducted into them. The usual indicator is the circuit starts to fail and/or the splitter gets hot to the touch.

Marine VHF / AM/FM splitters are combination of the two. In a good design, the VHF side is tuned for that bandpass and the AM/FM side should have a block of some type to prevent RF from getting in from the VHF radio (usually a transformer of some type). The problem is most commercial splitters are not very well designed, or designed with minimum requirements. Just enough to get by so to speak. Yes, these will fail and will damage the load on the other branch of the splitter. They can also damage the VHF connected to the antenna because that side could also fail causing a very high impedance and SWR which you will not see unless you have the correct test equipment. Your symptoms are indicative of a failed block on the AM/FM side allowing RF to enter your AM/FM radio. It is possible that the splitter is not designed to handle the high RF currents presented thus breaking down the protection. Yes, it may say it handles 25 watts, but I doubt it. Good splitters for this use are designed to handle twice the power rating if not more. Over protection is best.

Remember that we are already dealing with loses in the VHF path. We have the antenna at the top of the mast probably with a matching coil (induced loss), the RF cable from the radio set to the antenna (attenuation loss) and now we are inserting a splitter (additional attenuation loss). Regardless, as mention above, all splitters induce attenuation in the circuit and really have no place on a boat's VHF. This includes amplified splitters. Separate antennas are the best solution.

JMHO
 

MrUnix

.
Mar 24, 2010
626
Hunter 23 Gainesville, FL
As others have stated, a splitter is not an optimal solution and two separate antennas is best. But if you really want to use a single antenna, then your next best bet is to get an antenna switch so you can select between your VHF and stereo:



Cheers,
Brad
 
Nov 26, 2012
2,315
Catalina 250 Bodega Bay CA
MrUnix has steered you right if you must use only one antenna for FM/VHF. Just carry a spare switch and/or inline coax barrel in case the RF fries your switch as well. You won't need a splitter w/ the switch of course.

Chief (FCC lic. 1890)
 
Jul 1, 2009
221
Catalina 310 Sydney-Pittwater
Thanks for your advice, folks.

Took the boat out today: No interference of VHF transmitter with audio when starting out. After a 1 hour return under power, the problem reappeaqred. It seems that Brian D’s comment re higher powerload is spot on – the voltmeter showed 13.3V.

Have decided to follow your advices and connect the audio to a separate antenna.

To do this, I shall disconnect the audio from the sp;litter, but leave the latter connected as a lead from the VHF to the mast antenna, until I can find a connector for the latter. At this configuration the Sydney Rescue Service confirmed a clear transmission over about 10 miles.

For the audio, I am mainly interested in an FM antenna. I found 2 internal unused/unconnected cables, measuring about 5m leading from the control panel to the stern port locker. One is a coaxial, the other seems to be a 4 core speaker cable. I thought I could use either, a) by using the shield of the coaxial as the antenna wire or b) one or two of the speaker cores.

However, being rather clueless re electronics, how do I connect these wires to the radio? The female coaxial plug of the FM radio seems to imply that there is a + and – connection. How do I attach these to the cable wires? From bitter experience: + to – results in a short. Also, should I solder the ends of the cable wires to form a loop?

Sorry, to pose this question, which is probably a ‘no brainer’ to you all.
 
Sep 3, 2013
16
Columbia 8.7 ROCKLAND & ST. PETE
Hey, I was wrestling with how to antenna AM-FM and VHF together and was advised by Scott at Hamilton Marine (Maine) that mixing never produced great results and that I should keep separate. I followed recommendations and bought a Jensen antenna for the FM and hid it in my dodger-everything works great-so that's one possible solution-Cheers, Will


Recently I noticed that the AM/FM Radio lit up and the speakers made a noise whenever I pressed the send button on the VHF Mic, even though the radio was turned off , including at the fuse switch.

As disconnecting the FM aerial from the splitter stopped this problem, I replaced the splitter. The problem appeared solved. However, 1 week later I am having the same problem.

Also, when transmitting with the FM radio on, the sound of the latter is severely disrupted.

Do splitters breakdown and, could this problem damage any of the radios?

I do not really want to connect the FM to another aerial, as I think I need the mast height for reasonable reception in our area.
 
Oct 17, 2011
2,808
Ericson 29 Southport..
I have never seen a splitter or combiner to work well. The emphasis on 'well'. I know Brian is, and I are hams, along with some real techies here that will repeat that sentiment. That said, you don't have to know the jargon, SWR's, and resonating elements and whatnot. But every time I tried to combine an antenna, or a radio, (one of my working trucks had eleven radio's in it), it would never work seamlessly. I always went back to a dedicated whip.
From an electronic engineering perspective, it's near impossible. Splitters are a trade-off. And an invitation to let the smoke out of your radio. Expensive smoke.

(Here's a trick from the sneakaround dept. Paint your antennae semi-flat black. They turn near invisible).
 
Nov 26, 2012
2,315
Catalina 250 Bodega Bay CA
I am an Electronic Engineer and I endorse this message! Separate antenna are by far the best way to go. Chief
 
Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
I am an Electronic Engineer and I endorse this message! Separate antenna are by far the best way to go. Chief
Even if you have a "switch", not a "splitter", there is always the hazard of forgetting to switch to the VHF side. Forget to do that, and you can fry the FHF radio.:doh:
 
Jul 1, 2009
221
Catalina 310 Sydney-Pittwater
Again, thanks to all for your contributions. Have today disconnected the FM radio’s antenna inlet from the VHF splitter. The new connection to a free coaxial cable lying on the portside of the boat seems to work well, with the last 2-3ft of the inner core freed from the metal shield, but left insulated. The reception is as good as before.

Have decided to leave the cabling via the splitter connection as is, because a) can’t find a suitable connector, b) offshore radio check proved 5/5 and c) after dissecting the old splitter, exposed its mystique: All it had was a positive core leading from the antenna thru the splitter to same core of the VHF. The FM radio’s antenna inlet was connected via a plain wire to the VHF antenna’s metal shield. All this ‘complexity’ was encased in a hollow plastic box – total cost A$50- 60. What a Con.
 
Oct 9, 2008
1,739
Bristol 29.9 Dana Point
Again, thanks to all for your contributions. Have today disconnected the FM radio’s antenna inlet from the VHF splitter. The new connection to a free coaxial cable lying on the portside of the boat seems to work well, with the last 2-3ft of the inner core freed from the metal shield, but left insulated. The reception is as good as before.

Have decided to leave the cabling via the splitter connection as is, because a) can’t find a suitable connector, b) offshore radio check proved 5/5 and c) after dissecting the old splitter, exposed its mystique: All it had was a positive core leading from the antenna thru the splitter to same core of the VHF. The FM radio’s antenna inlet was connected via a plain wire to the VHF antenna’s metal shield. All this ‘complexity’ was encased in a hollow plastic box – total cost A$50- 60. What a Con.
Knowing the manufacturer would be valuable. If it's the same as mine (Shakespeare), then I'd know to toss it. I'd be surprised too, as my thinking is that Shakespeare is a reputable mfg. And, it would be odd that you had 2 failures back-to-back, and I've had 2 units that never failed. In any case, even though no problems I'm starting to think about 2 ants too.
 
Oct 17, 2011
2,808
Ericson 29 Southport..
Aw crap, I'll drone on for another second. Years ago, I cracked the case on a few of those things, very complicated times, but I've seen. One of them was from a major manufacturer that all would know, so there's no reason to think there brand was inferior, it was just like the others. Maybe the military or aeronautical industry builds intrinsically safe splitter/combiners, but I have never seen one personally that was safe for an expensive transceiver. Take a frequency counter, or spectrum analyser past the thing and they will go nuts. They leak, sometimes into your eyeballs, sometimes back to the other side of the splitter that you don't want.
I don't mean to sound rude, but if you have one that works, good deal. I would never own one though unless it had been vetted thoroughly. Don't let the smoke out, it's dangerous stuff. Think of the children..:)
 
Oct 9, 2008
1,739
Bristol 29.9 Dana Point
Oh NO!! When that guy stuck those wires in his mouth, haaaaaahaha. That's not Maine is it?
I love it later-on when he's melting the wire. After all that had already happened, it totally sums up the level of expertise. I just roll with laughter.
 
Jul 1, 2009
221
Catalina 310 Sydney-Pittwater
Knowing the manufacturer would be valuable. If it's the same as mine (Shakespeare), then I'd know to toss it. I'd be surprised too, as my thinking is that Shakespeare is a reputable mfg. And, it would be odd that you had 2 failures back-to-back, and I've had 2 units that never failed. In any case, even though no problems I'm starting to think about 2 ants too.

Not sure about the manufacturer, but certainly not Shakespeare-different shape and connectors. My replacement, that is also not performing, is locally manufactured (in China?).