Radio mic reception problems (on a boat!)

[Cheeseweasel]

Okay, here is a left-field suggestion : I once had a problem with RF on a large boat. It was an install so we had a tonne of time to work out the problem. The Ariels were hex-clamped to a metal rail on the upper deck. It turned out that the metal transducer of the echo-sounder wasn't properly isolated form the metal hull of the boat and the high frequency bleed through the hull was disrupting the much lower frequency radio mic channels. It took us days to work out the problem. Ironically, once we did, and got it fixed, the echo sounder worked much better too!

 

That's an interesting thought. The depth sounder and all other navigation systems and radios are turned off when we're in port though. The hull is used as the main earthing point for everything on-board, including the ship's generators and various switchmode power converters. I expect all manner of crap gets sent straight to the hull tbh.

[jamesperrett]

I've set up a number of wifi systems on ships as well as the odd UHF setup. There are a few things that I would think about. First, you talk about crackles and things cutting in and out. Have you absolutely eliminated the microphones, cables and transmitters from the cause of these problems? Do you have RF signal indicators on your receivers? What are they doing when you have problems?

 

The other possibility is that there are blind spots due to reflections from the ship's superstructure. You really need to spend a little time having someone walk around the ship with a transmitter while you monitor the signal levels. It is possible that a transmitter will work fine right next to the superstructure but moving a few cm forward will cause the reflection to destructively interfere with direct signal.

 

James.

[Cheeseweasel]

I've set up a number of wifi systems on ships as well as the odd UHF setup. There are a few things that I would think about. First, you talk about crackles and things cutting in and out. Have you absolutely eliminated the microphones, cables and transmitters from the cause of these problems? Do you have RF signal indicators on your receivers? What are they doing when you have problems?

 

The other possibility is that there are blind spots due to reflections from the ship's superstructure. You really need to spend a little time having someone walk around the ship with a transmitter while you monitor the signal levels. It is possible that a transmitter will work fine right next to the superstructure but moving a few cm forward will cause the reflection to destructively interfere with direct signal.

 

James.

 

Yes, there are several "problem areas" on the set that suffer from poor reception regardless of which transmitter/antennae/cables I use. The problems can be reduced slightly by careful positioning of the antennae. The RF signal indicators go red when the mics drop out and generally light up more than they should be doing (I have enough experience with radio mics to know how they behave in a 'normal' situation).

 

You are describing what I was afraid of - that the hull is creating some effect that is blocking/interfering with my radio mic signals. As was suggested by someone else, I think I'll experiment with using a second pair of antennae on the ship itself to cover the deck, and another pair covering the shore, finding some position where the pairs dont' interfere with each other.

[AndyW69]

Hi, are the adu's AKG? If yes they have a setting inside the circular cover on the front to compensate for cable length, the cables also make a huge difference

 

Andy

[AndyL]

If you are going to use all 4 antennas with combiners I would stick to the 4 paddles. In order to reduce multipath (which is already being exacerbated by your metal hull) you want to position the combined antennas so the areas they cover are in each other's nulls. You do not want a transmitter picked up by both antennas. You can get good passive combiners from Mini-Circuits

 

With the difference in performance between the HH and lav, there is also the chance that the antenna inside the belt pack is broken. This is not unusual with vigorous use. If you have access to an RF analyzer you can look at real signal strength of the transmitters to help you determine if the transmitter is at fault.

 

Mac

 

Beware of buying passive combiners in the wider RF market. Products such as the otherwise excellent Mini Circuits ones mostly do not pass DC, in fact are DC grouinded intrernally so if you have active antennas or boosters or head amps they will not get any power, and may blow fuses or worse in power supplies or RF DA's etc. The passive combiners supplied by radio mic manufacturers will usually take this into account, so do check this out before buying.

 

I second the comments about pocket pack aerials, but the other enemy of the pocket pack TX is body absorption. HH antennas are normally in relatively free air whereas body pack antennas end up close to the RF absorbing flesh, which can eat up 20dB of valuable UHF signal. Every extra mm of spacing between the TX antenna and the body that you can get will help.

 

And there is no such thing as 50 ohm RG 59. RG 58 is 50 ohm, RG 59 is 75 ohm. Sorry if someone else has already pointed that out.

[mackerr]

Beware of buying passive combiners in the wider RF market. Products such as the otherwise excellent Mini Circuits ones mostly do not pass DC, in fact are DC grouinded intrernally so if you have active antennas or boosters or head amps they will not get any power, and may blow fuses or worse in power supplies or RF DA's etc. The passive combiners supplied by radio mic manufacturers will usually take this into account, so do check this out before buying.

 

Thanks Andy, I meant to include a note that active antennas would need separate power supplies, I hadn't thought about the DC short to the existing PS. We use these all the time, maybe the shops are building in a DC blocker cap to protect against that. If feasible I try to avoid active antennas to eliminate another point of IM creation, but the distribution well be the same whether we use active or passive antennas on it.

 

Mac