996XT poor low band reception when serial port connected

[oracavon]

Whenever I connect the rear serial port of my 996XT to a PC, even when the radio is turned off, low band reception of all the radios on my bench gets poor. The problem affects only VHF low band. This prevents me from controlling the radio via a serial connection if I'm monitoring any low band channels. I have two 996XT radios, and they both do the same thing.

Has anyone else seen this issue? Any solutions?

 

[davidmc36]

I have seen that for a couple scenarios on my 396XT. It will totally lose a VHF (140's) Control Channel that was coming in at 4/5 bars. It will also wipe out an 800mhz CC trying to run it with Unitrunker and DSD, although that one is not as strong a signal to begin with.

 

[KE5MC]

Not sure with the information supplied my comments fit, but they might.

If the antenna connection is open it could be receiving via the shield connection. When you connect the serial connector a better/different ground is made reducing the shield connection reception.

I wrote the above having seem many times where the center conductor on the coax was shorted to the shield and receiver noise was high as the connector was being attached until the center pin made connection. Then all went silent.

Taking the shorted center pin idea and extrapolating to your situation, which may or may not work.

Good luck, let us know what you find.

Mike

Whenever I connect the rear serial port of my 996XT to a PC, even when the radio is turned off, low band reception of all the radios on my bench gets poor. The problem affects only VHF low band. This prevents me from controlling the radio via a serial connection if I'm monitoring any low band channels. I have two 996XT radios, and they both do the same thing.

Has anyone else seen this issue? Any solutions?

 

[davedaver1]

For what it's worth, my wi-fi (2.4 gHz) causes all kinds of grief on low band. Router off, silence. Router on, noise on low band. \In my case, it's noticeable in certain areas, not in others. Computers are notorious emanators anyway with everything constantly cycling, power supplies to motherboards to video cards.

 

[Redgum]

A couple things to consider here:

1. Shield ground for all your equipment is very important. This doesn't mean simply using a 3-prong power cord. This means driving one or more 8' long copper grounding rods into good earth (consider using a chemical ground if you live in the southwest) near where your equipment resides and connecting the grounding lugs to a 00# AWG bus. Use braided grounding wires to connect your rigs to the ground bus. There will be a noticeable difference in the noise levels and your ability to pull signals out of the bacon when you have properly grounded ALL of your gear.

2. USB signal cables come in two varieties: CRAP and reasonably good. If you are using cheap USB cables (ones without a braided shield) and have connected USB cables that do not come with RFI chokes, then you are essentially hooking antennas to all those oscillators in your PC. Some peripherals are sold with CRAP cables. CRAP cables may work o.k. in 99% of all US households, but if you're an SWL / Scanner / Ham enthusiast, then you are the 1% of households that those CRAP cables should not be found in. Be selective...be very selective.

 

[oracavon]

Thanks for the ideas.

I know the antenna connections are good. However, I am using unshielded RS-232 cables (not USB), so I think I will try shielded cables to see if that makes any difference. I'm thinking that it's got to be something radiating from the cables, since it affects all my other radios on the bench. The problem comes and goes with the RS-232 electrical connections - I can make the problem instantly come and go just by touching the RS-232 wires to the back port of either radio, without touching or moving anything else.

 

[scosgt]

How about adding RF chokes to the serial cables. I actually have them on my serial cables.

 

[oracavon]

How about adding RF chokes to the serial cables. I actually have them on my serial cables.

Hey, that's a good idea. I wish I'd thought of that when I was at Radio Shack earlier today. I'll get a couple next time I'm out. Thanks.