BCD325P2/BCD996P2: BCD996P2 Grounding

[k7stq]

I recently added this scanner to my ham shack and get great reception using a roof-mounted discone. Having an issue, though, involving other connections from the same antenna to an Icom 746Pro transceiver and Icom R8500 wideband receiver. A Diamond three-way switch connects all three rigs via RG58 / LMR240 cables.

The scanner won't receive properly when the other radios are connected ... it clicks after powering up instead of the usual beep and there's no audio.

I've read the warning in the scanner manual about not grounding and have not done so, but my other radios are necessarily grounded. All radios sit on my desk and connections are on a shelf behind the desk that's covered with a sheet of aluminum to create a ground plane. The Icoms are connected via DC to a RIGRunner and the scanner is powered through the AC adapter.

Thanks for any guidance on a permanent solution so I can avoid disconnecting the patch cables to the Icoms when listening to the scanner!

 

[buddrousa]

Sounds like your system has no common ground to all three. I would try turning over the AC adapter for the scanner or option 2 run all 3 on the same DC power supply.

 

[tvengr]

Is the 996P2 stopping on frequencies and talkgroups or is it not scanning properly? If the other radios are turned off or if power is removed, does it make a difference?

 

[maus92]

Sounds like your system has no common ground to all three. I would try turning over the AC adapter for the scanner or option 2 run all 3 on the same DC power supply.

It does share an antenna shield ground I would think.

 

[n1chu]

What happens when you disconnect each of the other radios individually?

I expect the grounding warning you see in the scanner manual has to do with lightning protection, (a 4 foot ground rod you drive into the earth) and is not concerned with reception (although a proper ground is half of your antenna… the discone is the other half.)

The shielding you have between the radios in the shack may help the transceiver (when transmitting) reduce generating interference into the receivers but it’s not the antenna ground I refer to as the other half of your scanners antenna.

 

[buddrousa]

I am looking at the power plug of the 996p2 being turned over or see inducted AC on the coax being run beside AC line and the scanner is not as tolerant of the voltage.

 

[n1chu]

1) Turned over? What’s that mean?

2) Isn’t the power cord on a 996 a wall wart that supplys DC, not AC? Therefore, no induced current onto the antenna coax.

 

[k7stq]

1) Turned over? What’s that mean?

2) Isn’t the power cord on a 996 a wall wart that supplys DC, not AC? Therefore, no induced current onto the antenna coax.

Thanks for the helpful thoughts. The scanner appears to function fine when this problem occurs ... I can even see bars when it's receiving but there's no audio. FWIW, both Icoms also have an HF antenna and the scanner works when those cables are connected.

Rotating the Uniden wall wart in the outlet did not resolve things but I'll check the antenna ground. Will likely connect the scanner to the DC power strip, too, just to have all the radios there.

Merry Christmas everyone!

 

[tvengr]

If the other radios are turned off or if power is removed, does it make a difference?

You didn't answer that question. Oscillators in the other radios could be radiating signals which interfere with the scanner. Also, unplug any USB power supplies. They are notorious for causing interference. Does the scanner receive NOAA weather? You could have a dirty headphone jack muting the speaker. It is also possible that your ICOM transmitted close by or directly into the scanner and blew the RF amp.

 

[k7stq]

You didn't answer that question. Oscillators in the other radios could be radiating signals which interfere with the scanner. Also, unplug any USB power supplies. They are notorious for causing interference. Does the scanner receive NOAA weather? You could have a dirty headphone jack muting the speaker. It is also possible that your ICOM transmitted close by or directly into the scanner and blew the RF amp.

Yeah ... sorry. I meant to clarify the scanner is affected even when the Icoms are turned off. I've been listening to the scanner via an external speaker. After reading your question about a mic jack, I discovered the audio cord is the problem. Unplugged it, reconnected the cables and the scanner's works just fine. Good troubleshooting! I hadn't grounded the speaker yet due to the Uniden manual warning ... but maybe that's the root cause.

 

[tvengr]

What type of external speaker are you using?

 

[bearcatrp]

I just tried a T connector for my 8500 so both coax out of the back, HF and VHF/UHF, of the 8500 can go to my discone antenna which is LMR400. The T connector has a loss of 4s on my meter. Connected, got 1s but running VHF direct got me 4.5s. You may want to check to make sure your switch isn't causing issues.

 

[k7stq]

What type of external speaker are you using?

My speaker is an Icom SP-21 with a splitter at the end of the audio cable to feed the 8500 and scanner (now disconnected).

Bearcatrp: I use Diamond antenna switches and have two ... one for HF to my 8500 and an Icom 746 Pro and a three-way for VHF to those radios and the scanner. It does appear the speaker / audio connections are the issue as the scanner will work fine when antenna coax is connected to all three radios and I use the scanner's built-in speaker instead of an external. Scanner audio fails when I plug in the external speaker jack and will only work if I disconnect the VHF coax to the other two radios.

 

[JoeBearcat]

My speaker is an Icom SP-21 with a splitter at the end of the audio cable to feed the 8500 and scanner (now disconnected).

Bearcatrp: I use Diamond antenna switches and have two ... one for HF to my 8500 and an Icom 746 Pro and a three-way for VHF to those radios and the scanner. It does appear the speaker / audio connections are the issue as the scanner will work fine when antenna coax is connected to all three radios and I use the scanner's built-in speaker instead of an external. Scanner audio fails when I plug in the external speaker jack and will only work if I disconnect the VHF coax to the other two radios.

The 'other' radio is shorting out the audio. Use separate speakers or use audio isolation.

 

[richwig]

The 'other' radio is shorting out the audio. Use separate speakers or use audio isolation.

It's never a good idea to Y-together speaker outputs of equipment. Back in the day when speaker outputs had transformer isolation, you might have gotten away with it. Today's direct-coupled amp designs won't tolerate that, and could lead to damage.

 

[maus92]

Yea, don't be a cheapskate (lol!) You can buy used Moto communications speakers on eBay for $10-$20, and Logitech amplified computer speakers for $20-30 new. Worth it.

 

[iMONITOR]

Is there a Bias-Tee (12VDC inserter) for a preamp installed on the coax?

 

[k7stq]

Thanks Joe and all ... really appreciate the helpful advice. I'm planning to get another speaker for the scanner. Looking at West Mountain's option and will check out Logitech too. I mostly use headphones on the 746 so the first speaker can be dedicated to the wideband receiver.