Having some RFI issues in my Audio

[W5EFR]

Hello Gents.

I am running rack gear on my Icom IC-718, and the audio is fed through the ACC jack on the back.

I have been running on SSB and I have not had any issues with RF in the Audio, but I am starting to get the itch to play with AM and I am now having issues.

No matter where I set the carrier power on the rig, I'm getting RF, I can hear it when I start adding enough audio to just start modulating the carrier, and I can hear the RF audio in the Carrier, even when I am not saying anything.

The Audio Chain is:
-MXL V57 Condenser or a modified Nady RSM-4 Ribbon Mic
-Behringer VX-2000 Mic Preamp
-Behringer PEQ-2200 Parametric EQ
-Behringer EX-3200 Ultraflex Pro
-DBX 266XL Compressor/Limiter
-Behringer MX-602A Mixer
-Rolls DB-25 Isolation box
...then to the radio through the Accessory Jack in the rear.

My audio chain is all Balanced XLR, except from the mixer output to the Roll DB-25 direct box.

So far, I have:
-Double checked my XLR cables to confirm they are wired correctly
-Added bypass caps to the mic cable input to the mic preamp
-Checked my grounding
....everything seems OK

No luck yet...

Anyone have any other suggestions? 

Thanks

[w8khk]

With so many components in the audio chain, the first step is to determine where RF is getting in.  Start by closing the master level control on the mixer, if the problem is gone, the source is toward the mic input.  Still there, look toward the rig.  Work one component at a time to determine where the RF is getting in.

Are you using short XLR cables, or long ones coiled up?  If you find the location where RF is entering the audio chain, perhaps some clamp-on ferrites on the XLR cables or power cables might tame it. 

Instead of monitoring in the rig, place a scope on the output of the direct box, and you might find it easier to troubleshoot with lower carrier power.  The scope will also make it possible to validate whether changes to the configuration improve or degrade the situation. 

[W1EUJ]

Too much equipment.

[W5EFR]

Thanks for the reply Rick

With so many components in the audio chain, the first step is to determine where RF is getting in.  Start by closing the master level control on the mixer, if the problem is gone, the source is toward the mic input.  Still there, look toward the rig.  Work one component at a time to determine where the RF is getting in.

Yes, I have determined that the RF is getting into the audio chain, I shut down the master on the mixer last night, and sure enough, the carrier was silent.

Are you using short XLR cables, or long ones coiled up?  If you find the location where RF is entering the audio chain, perhaps some clamp-on ferrites on the XLR cables or power cables might tame it.

The XLR cables interconnecting the rack components are as short as possible. The power cables are the ones that came with the units, and they are all run into a Datalink power conditioner on the rack.

Instead of monitoring in the rig, place a scope on the output of the direct box, and you might find it easier to troubleshoot with lower carrier power.  The scope will also make it possible to validate whether changes to the configuration improve or degrade the situation. 

OK, great Idea, I'll try that tonight.

Thanks for all the input.

Too much equipment.

Thanks for the input, but that doesn't help much....

[Mike/W8BAC]

Are you sure it is RF? Could it be 60 cycle? Not second guessing you Scott but it is common to introduce 60 cycle when you add a bunch of accessories like you have.

Mike

[W5EFR]

Thanks Mike, I think Its RF, but I could be wrong....

I PM'd you a link to a link to an audio sample.

Can you tell me what you think?

Let me ask this...

Is it possible to have RF with AM mode, but not SSB?

I have been running this setup for about a year on SSB and never had any RF in the audio complaints

[W2XR]

Too much equipment.

Yes, I agree. You can have too much of a good thing.

In all things audio, less is always better. Use the minimum amount of equipment to do the job. You should need nothing more than a good microphone preamp, EQ, and limiter/processor, and that's it.

73,

Bruce

[W5EFR]

listening to the recording I made, the RF is into the signal before I even start turning the rack components on... it is getting in at, or before the preamp...

I think I'll build a new mic cable for starters....

[Pete, WA2CWA]

No mention if you're running a linear. You could also try an RF sniffer (microamp meter with a 1N34 across the terminals and a short antenna hooked to the anode terminal) to sniff around your audio maze when you key the rig in the AM mode.

[ka3zlr]

Hello Gents.

I am running rack gear on my Icom IC-718, and the audio is fed through the ACC jack on the back.

I have been running on SSB and I have not had any issues with RF in the Audio, but I am starting to get the itch to play with AM and I am now having issues.

No matter where I set the carrier power on the rig, I'm getting RF, I can hear it when I start adding enough audio to just start modulating the carrier, and I can hear the RF audio in the Carrier, even when I am not saying anything.

The Audio Chain is:
-MXL V57 Condenser or a modified Nady RSM-4 Ribbon Mic
-Behringer VX-2000 Mic Preamp
-Behringer PEQ-2200 Parametric EQ
-Behringer EX-3200 Ultraflex Pro
-DBX 266XL Compressor/Limiter
-Behringer MX-602A Mixer
-Rolls DB-25 Isolation box
...then to the radio through the Accessory Jack in the rear.

My audio chain is all Balanced XLR, except from the mixer output to the Roll DB-25 direct box.

So far, I have:
-Double checked my XLR cables to confirm they are wired correctly
-Added bypass caps to the mic cable input to the mic preamp
-Checked my grounding
....everything seems OK

No luck yet...

Anyone have any other suggestions? 

Thanks

Hello there,

 Nice "Rack-o-Gear" OM,... .. First what is the location of Antenna, directly overhead..off to the side a little,... way back in the back yard..?...Further away the better.....Step one.

After yer Done sniffing around..."Separate the Gear"...Amplifiers and Antenna Couplers in their own area not directly stacked on or near the Transceiver and Audio chain...Near Field Effect here, OM..."Think near Field Effect"...before tearing things down move them... and monitor what changes...Does the Transceiver display a waveform distortion with the Mic Cable unplugged...ETC...

With that type of Stack you shud break the Audio chain often, an in between each component..if possible....ie gud isolation transformers.. Jensen JT-11-P...can get expensive but if yer gona play audio.. think isolation OM...gud rule of thumb...One Nice little item that may help...is the IHY IBox at the Mic input...Breaks the line and has Acceptable filtering...Think about it...http://w2ihy.com/ibox.asp ...it is OP buildable...have used it and It werks...copy the Skizmatic build yer own install internally at the input of the rig...

OK, Now, DC supplies...Never in the Immediate Vicinity of RF generators...Again separate move to the floor further away from RF the better...How is yer station AC supply Any filtering..?...Connections, clean nice an tight,... Check AC Ground..Clean Connections..?......all grounds Connected...

You have a very simple problem and it will have a very simple cure..you have to find it...these are some gud ideas and some things to consider...

Let us know what happens OM...

[N5RLR]

Something in the back of my mind is nagging that it may be that accessory jack or internal circuitry thereto.  Can you try through the "normal" mic jack for a comparison, Scott?

[N3DRB The Derb]

-MXL V57 Condenser or a modified Nady RSM-4 Ribbon Mic
-Behringer VX-2000 Mic Preamp
-Behringer PEQ-2200 Parametric EQ
-Behringer EX-3200 Ultraflex Pro
-DBX 266XL Compressor/Limiter
-Behringer MX-602A Mixer
-Rolls DB-25 Isolation box
...then to the radio through the Accessory Jack in the rear.

Dude, you tryin to stuff dolly parton's boobies into a 34 B cup. Do you know what freq response the Icom is good for?

and yes, I know I didnt solve yer question - but that impresses me as way too much audio chain. Take all that stuff out of there until you get rid of the RF, then add them back on one at a time and isolate the box giving you the problem. 

[w3jn]

Don't neglect the possibility of RF getting into the equipment thru the AC power.  I connected up a cheapo mixer and in QSO with the HUZman, he asked if I had some BC SW station on in the background... long story short, RF getting into the mixer thru the AC power, mixing with some strapping BC SW station in the PS diodes.  Some .01/2KV caps from each leg of the AC where it entered the box to the chassis ground stud solved it.

[WD8BIL]

Hi Scott,

I'm running the 718 with external audio also. I have the MXL990 into a MX-802.
I go directly from the mixer to the radio and put the nano compressor in the aux send/return loop.
The radio drive an amp to full power. No RF problems so far.

Ya might wanna try stripping down to the mic/mixer/radio barebones configuration and see ifn that helps. I wouldn't use the mic preamp with the 602. Just plug the mic straight into the board.
Which brings up a thought.
Are you putting the output from the preamp into a mic input or line level input?

[W5EFR]

Last night, I injected a 1kHz signal into the mic end of the mic cable....

Stuck my O'scope on the mixer output....

I could not see any noise on the 1khz signal when I keyed up the transmitter.

The Antenna is in the backyard, it is a vertical with the base about 25' up.

But I have been doing my testing with a dummy load in the shack, but the RF gets into the signal either way....

Take all that stuff out of there until you get rid of the RF, then add them back on one at a time and isolate the box giving you the problem. 

Thanks, I'll try that tonight

Something in the back of my mind is nagging that it may be that accessory jack or internal circuitry thereto.  Can you try through the "normal" mic jack for a comparison, Scott?

I am going to build a cable to interface the Mic jack with the rack today, but if that is the answer, I'll have to modify the radio to get and real frequency response out of it, the ACC Jack bypasses all of the "Voice Optimized" (aka DX'er Audio Heaven) Tone filters that the mic input circuit has.

Hi Scott,

I'm running the 718 with external audio also. I have the MXL990 into a MX-802.
I go directly from the mixer to the radio and put the nano compressor in the aux send/return loop.
The radio drive an amp to full power. No RF problems so far.

Ya might wanna try stripping down to the mic/mixer/radio barebones configuration and see ifn that helps. I wouldn't use the mic preamp with the 602. Just plug the mic straight into the board.
Which brings up a thought.
Are you putting the output from the preamp into a mic input or line level input?

I have been running the mic into the mic input (as apposed to the 1/4" LINE input of the preamp).

How are you interfacing the radio? the Mic Jack or the ACC jack?

[AF9J]

Hmmmm,

Here's a thought some of you may not have considered.  It may be as simple as RF feedback.  Back in college in the 80s, I had a similar problem with an FT-101B (absolutly horrible phone audio on 160m).  It turned out to be RF feedback.  When I had my IC-703 Plus a few years back, I had to revisit the RF feedback issue again.  If I'm right, like the '703 Plus I used to own, the IC-718 is a single board radio, and like the IC-703 Plus, is descended from the IC-706 series.  Single board radios can occasionally have grounding issues.  On 40m, my '703 Plus used actually shut down if I transmitted on certain freqs.  I'd say re-inject the 1 kHz signal into your '718, but do it with the antenna hooked up, and then check your scope.  Also, check different bands.  On some bands I had no problems at all.  On other bands (specifically 40 & 15m), I had problems with RF feedback.  I never did completely get rid of the problem.  But, installing ferrites & chokes on the power and CW key cables, and a common mode current choke on the feedline (near the radio end of things), did help quite a bit. 

73,
Ellen - AF9J

[flintstone mop]

Lotta gud stuff here for troubleshooting.
You can try to choke off the feedline from the vertical. Help folks....is it a 1:1 current balun that would isolate the aerial from the shack?
Verticals are usually problems with RF feedback.
You can also try wrapping AC supply cords or mic cords in those ferrite clamps sold at ShadioRack, if they still sell them.
Audio equipment sounds like a little much, but the proof is in the pudding. I, like the others, would be concerned that the processing is beyond the audio specs of your off-shore tranceiver.

Fred

[W1DAN]

Hi Scott:

My 2 cents worth:

Behringer gear does not have much in the way of RF filtering. If you open your mixer's master and the RFI begins, then it can be getting into

1) the mic (behringer mics are not shielded and having an active amp in it causes problems)

2) the mic preamp

3) the mixer.

One thing to try is run a ground strap from the transmitter to all affected gear (even the mic XLR at the mic) to attempt to bring all the gear to the same (hopefully low) RF point. You may need to filter the AC line as mentioned or the audio ins and outs in each box, or even put the offending item in another shielded box (drastic).

Being a processor nut, I have found that too much gain reduction (compression and limiting through many boxes) can make a very small amount of RFI very pronounced and difficult to resolve. I have solved it though in the past.

Hope all these ideas from everyone helps. Let us know what you find!

73,
Dan
W1DAN

[WD8BIL]

How are you interfacing the radio? the Mic Jack or the ACC jack?

The ACC jack, Scott.
AND.... it's all unbalanced.

[W1EUJ]

http://www.w5efr.wz5q.net/index/pic/chain.jpg

He's got a website describing his setup fairly well.

http://www.w5efr.wz5q.net/index/pic/graph.gif

Frequency Sweep.

David Goncalves
W1EUJ

[W5EFR]

http://www.w5efr.wz5q.net/index/pic/chain.jpg

He's got a website describing his setup fairly well.

http://www.w5efr.wz5q.net/index/pic/graph.gif

Frequency Sweep.

David Goncalves
W1EUJ

Hey David,

Yup, that was my setup... I might change it back to something like that...

The current setup is here:

http://riley-music.com/BowsStuff/SSB_Audio/W5EFRAudioChain.JPG

This is a better graphic of that same sweep, which I did after modifying the radio for 3.3 kHz on SSB:

http://riley-music.com/BowsStuff/SSB_Audio/3khz718.gif

How are you interfacing the radio? the Mic Jack or the ACC jack?

The ACC jack, Scott.
AND.... it's all unbalanced.

Thank you for the information, Bud.
I'll keep hammering away at it.

[WBear2GCR]

Grounding too...

I'd monitor the output of the Rolls or the Mixer with the rig keyed into the dummy load, since you say the RF is there into the dummy load - key the rig and look at the output of the mixer/Rolls with the scope. Assuming the scope is good past the frequency of interest of course. Then work backwards.

Alternately, turn things on from the Rolls back and look for the RF to appear.

Imho, you might have had RF in ur audio all along, but on SSB with the usual inherent distortion and the ALC that is usual even inside a typical SSB rig, a little extra RF might not get noticed. Possibly. On AM it is much easier to hear this sort of thing.

                    _-_-bear


PS. A sweep won't show much in the way of RF getting in - since that is distortion. For that a look at a simple sine wave will show it up as a thickening of the trace everywhere or in one or two places... For AM you'll likely want bandwidth out to 5khz. although the Icom may or may not pass audio out there.

[ka3zlr]

Is the rf online when the computer is connected, there's a loop there OM. You May Have Computer issues here..

[Mike/W8BAC]

Is the rf online when the computer is connected, there's a loop there OM. You May Have Computer issues here..

Please explain this Jack.

[WD8BIL]

Scott.... the line from the compressor to the mic input on the 602........ try pulling this out and run the compressor output to one of the line level inputs. These can be wired balance with a TRS 1/4" plug.