Filtering Interference

[TeK-NO]

I have some unwanted interference coming in on my marine radio the antenna is properly grounded. This started to happen recently after they activated a new repeater and now I am getting lots of inference once some channels are open on the trucking system.
I know that there are filters that I can use but I need help in choosing the right one for this application. The interfering frequencies are anything from 159.200mhz and to 161.00mhz

 

[Ubbe]

It depends of the trunking systems frequency. If they actually are in 159-161MHz, right in the middle of marine duplex band, there's nothing to do than to get a better marine radio that can handle strong signals. If they are in the 165-175Mhz range, then you'll need a bandstop or notch filter for that range, or a low pass filter or bandpass for the marine frequency range. You can ask PAR electronics for one that will be some $100-120.

/Ubbe

 

[devicelab]

I don't know if Ubbe misread your post but you need to be careful here. Certain filters are receive-only cannot handle more than 1/2 watt of power. You'd need a filter that is rated for transmit. The problem is that these can be quite expensive.

Are you sure it's interference from a new trunk site? Could it be pager interference?

PAR does make a 25w paging filter for Marine VHF. Check his page for details: https://www.parelectronics.com/marine.php

Ideally you need to know more about the problem signal. If you're sure it's from a new transmitter in the area, then you could try contacting the company directly.

A cheap ($30) SDR could help determine more about the specific nature of the interference. This is almost mandatory in deciding how to fix the problem.

PS. Also checked for the obvious -- bad, low-quality coax cable can also cause major problems. If the radio is an older model, then it's possible that it can't handle strong, adjacent signals and may need to be upgraded.

Good luck!

 

[Ubbe]

I don't know if Ubbe misread your post but you need to be careful here. Certain filters are receive-only cannot handle more than 1/2 watt of power. You'd need a filter that is rated for transmit. The problem is that these can be quite expensive.

You are absolutely correct about that. But the max power handling are often set for where a filter attenuates and all the power stays in the filter. If a filter only attenuate 1dB at the transmit frequency then in most cases it can handle a lot of power, as the power that stays in the filter are minimal.

/Ubbe

 

[iMONITOR]

It's possible that some of the truckers are using marine band radios. I've heard hunters several times using the marine band walkies-talkies in the woods!

 

[Ubbe]

I've heard hunters several times using the marine band walkies-talkies in the woods!

In my country that's totally legal. They share the leisure channels L1 and L2 with hunters with the restriction that hunters must not use them near shorelines. Maybe it's the same in US.

/Ubbe

 

[mmckenna]

Maybe it's the same in US.

It's not. Marine VHF is restricted to use on the water, and immediately adjacent for loading/launching.
Inland, there are some (not all) VHF marine channels that get reused for traditional LMR use, but it's under the Part 90 rules and off the shelf Part 80/Marine VHF radios are not permitted.

There are other users, but most of it isn't legal. Unfortunately most of the retailers sell Marine VHF radios right next to FRS/GMRS radios. The average consumer doesn't know the difference.

And, no, there isn't much enforcement.

 

[mmckenna]

I have some unwanted interference coming in on my marine radio the antenna is properly grounded. This started to happen recently after they activated a new repeater and now I am getting lots of inference once some channels are open on the trucking system.
I know that there are filters that I can use but I need help in choosing the right one for this application. The interfering frequencies are anything from 159.200mhz and to 161.00mhz

Those frequencies are right in the Marine VHF band.
Filtering them out may be problematic if you want the marine VHF radio to work properly.

I would be interested to know who/where this is. If it's well away from "navigable waterways", then it does happen where it shouldn't interfere with marine VHF users, usually well inland. If you are a legit user of Marine VHF, then you could file an interference report with the FCC, but don't expect much.
Keep in mind that some marine VHF radios are better than others for handling strong adjacent channel type interference. If this is a scanner or cheap VHF radio, you may need to upgrade.

 

[iMONITOR]

I would think if they made VHF marine radio legal for inland use, so many miles from any water it wouldn't cause any problems. Not any I can think of.

The ideal solution is one of the GMRS/Marine dual-band radios.

 

[mmckenna]

I would think if they made VHF marine radio legal for inland use, so many miles from any water it wouldn't cause any problems. Not any I can think of.

Well, it's used by Part 90 licenses in many inland locations, so if the FCC can sell that to paying users, they won't give it away for free. Plus, there are suitable radio services for consumer use: MURS, FRS, GMRS, CB, etc. The big issue is that end users don't know the difference between radio services and buy purely off the looks of the radio, or the advertised wattage. A lot of this started when one of the manufacturers started selling camouflage radios and retailers started carrying them at sporting goods stores aimed at hunters. There's been little effort to discourage that sort of use.

But, all it would take would be some hunter on a mountain top with a 5 watt VHF radio and they could screw up quite a big area.

The ideal solution is one of the GMRS/Marine dual-band radios.

Maybe, but current GMRS rules prevent that.

The real solution would be for consumers to take 5 minutes to educate themselves before buying radios, but we all know that's not going to happen.

 

[iMONITOR]

Marine/GMRS dual-band radios:

Cobra MR-HH450 DUAL Combination Marine and GMRS Radio

The Cobra MR-HH450-DUAL All-Terrain-Radio™ gives you the power to communicate on both land and open water!

www.buytwowayradios.com

ATLANTIS 290 Dual Band Marine VHF and GMRS Radio

Dual band marine VHF and GMRS radio. 22 Channels and 10 hour battery life. Product Overview Atlantis 290 radio combines a powerful marine VHF radio featuring all NOAA weather channels with a GMRS radio. JIS7/IPX7 Submersible Waterproof level + Designed to Float - So you can use it just about...

uniden.com

 

[mmckenna]

Marine/GMRS dual-band radios:

Cobra MR-HH450 DUAL Combination Marine and GMRS Radio

The Cobra MR-HH450-DUAL All-Terrain-Radio™ gives you the power to communicate on both land and open water!

www.buytwowayradios.com

ATLANTIS 290 Dual Band Marine VHF and GMRS Radio

Dual band marine VHF and GMRS radio. 22 Channels and 10 hour battery life. Product Overview Atlantis 290 radio combines a powerful marine VHF radio featuring all NOAA weather channels with a GMRS radio. JIS7/IPX7 Submersible Waterproof level + Designed to Float - So you can use it just about...

uniden.com

Right, and those are discontinued. I believe 80.203 shut that down.

 

[iMONITOR]

Right, and those are discontinued. I believe 80.203 shut that down.

So if you could find one are they now illegal to own or use?

 

[mmckenna]

So if you could find one are they now illegal to own or use?

I don't know how the FCC would view that.

 

[iMONITOR]

I don't know how the FCC would view that.

I always planned on getting a couple for my BOB (Bug-Out-Bag), especially living very close to the great lakes. That a hand-held VHF aircraft transceiver.