Topics

RFI on 2 meters from uBitx


Jay - WS4JM
 

I have been experiencing RFI on the 2 meter band when my V3 is tuned to the upper end of 75 meters. I had my uBitx tuned to the TN Phone net at 3.980 MHz and my 2 meter rig tuned to my local repeater at 146.91 MHz. The 2 meter rig showed full scale receive, with no audio. I checked with my hand held and it was full scale at least 50 feet from the uBitx. The RFI exists when the uBitx is in RX as well as TX. Seems like a 3rd harmonic of a mixing product; (45 MHz+3.98 MHz) X 3 = 146.94 MHz

Any ideas where or how to add shielding or if a component needs to be replaced?

Thanks,
Jay
WS4JM


 

You could try replacing relays KT1/2/3 with Axicom RF relays, that should reduce this.
Check earlier posts for details.

Raj

At 18/06/2020, you wrote:
I have been experiencing RFI on the 2 meter band when my V3 is tuned to the upper end of 75 meters. I had my uBitx tuned to the TN Phone net at 3.980 MHz and my 2 meter rig tuned to my local repeater at 146.91 MHz. The 2 meter rig showed full scale receive, with no audio. I checked with my hand held and it was full scale at least 50 feet from the uBitx. The RFI exists when the uBitx is in RX as well as TX. Seems like a 3rd harmonic of a mixing product; (45 MHz+3.98 MHz) X 3 = 146.94 MHz

Any ideas where or how to add shielding or if a component needs to be replaced?

Thanks,
Jay
WS4JM


Evan Hand
 

Jay,
Ensuring that it is installed in a metal case that is grounded is the only thing that I could see helping.  Are there any modifications installed?

What you are seeing is the 3rd harmonic of the Clock2 out of the SI5351 that is used in the first mixer to convert the incoming RF to the 45 MHz IF frequency.  That is not a mixing product.  It is the local oscillator for the conversion to 45 MHz IF.  Those signal traces are fairly short, so not much of an antenna.  Also, since it is on both transmit and receive, I doubt that the first mixer is damaged. 

I will see if one of my ubitx has the same issue.

73
Evan
AC9TU


Ashhar Farhan
 

It could be lack of shielding on the two meter rig too. We have swept the output of ubitx, there are very very small spurs at 2 meters. Indeed, it would be a wonderful surprise to find the venerable IRF510 shaking a leg on 144 mhz.
I hope 80 meter antenna is well matched.

On Thu 18 Jun, 2020, 5:41 PM Raj vu2zap, <rajendrakumargg@...> wrote:
You could try replacing relays KT1/2/3 with Axicom RF relays, that should reduce this.
Check earlier posts for details.

Raj

At 18/06/2020, you wrote:
>I have been experiencing RFI on the 2 meter band when my V3 is tuned to the upper end of 75 meters. I had my uBitx tuned to the TN Phone net at 3.980 MHz and my 2 meter rig tuned to my local repeater at 146.91 MHz. The 2 meter rig showed full scale receive, with no audio. I checked with my hand held and it was full scale at least 50 feet from the uBitx. The RFI exists when the uBitx is in RX as well as TX. Seems like a 3rd harmonic of a mixing product; (45 MHz+3.98 MHz) X 3 = 146.94 MHz
>
>Any ideas where or how to add shielding or if a component needs to be replaced?
>
>Thanks,
>Jay
>WS4JM





Evan Hand
 

Ashhar Farhan and Raj,

The original email stated that it was there on both transmit and receive.  I think that should rule out the relays, any of the transmitter amplifier stages, and the antenna match.  I guess it is possible that a bad match could affect the 30 Mhz LPF at the input to the first IF,  Still, the double-balanced mixer should isolate the LO from the RF port.

Am I missing something?
73
Evan
AC9TU


Dale Parfitt
 

Regarding the 2M issue, you might also try disconnecting your HF antenna and see if the issue goes away. If it does, then some #43 snap on ferrites right where the antenna coax exits the BitX should help- same for the key, mic and power leads. Of course, if the rig is not in a metal cabinet then all bets are off.

 

Dale W4OP

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Evan Hand
Sent: Thursday, June 18, 2020 8:17 AM
To: BITX20@groups.io
Subject: Re: [BITX20] RFI on 2 meters from uBitx

 

Jay,
Ensuring that it is installed in a metal case that is grounded is the only thing that I could see helping.  Are there any modifications installed?

What you are seeing is the 3rd harmonic of the Clock2 out of the SI5351 that is used in the first mixer to convert the incoming RF to the 45 MHz IF frequency.  That is not a mixing product.  It is the local oscillator for the conversion to 45 MHz IF.  Those signal traces are fairly short, so not much of an antenna.  Also, since it is on both transmit and receive, I doubt that the first mixer is damaged. 

I will see if one of my ubitx has the same issue.

73
Evan
AC9TU


Evan Hand
 

Dale's message prompted me to think of other cables that run near the Raduino.  By chance are you using CAT from the rig?   Snap a ferrite on it and any digital mode cables. 

Dale,
A good suggestion for the ferrites.  I already have them on my rigs because of RF feedback.

73
Evan
AC9TU


Dale Parfitt
 

Hi Evan,

While there can be a good deal of math involved to optimize ferrite common mode choking impedance, it  so easy to do trial and error that for most cases we can forgo the math.

I had  a serious distortion issue when I was connecting my Drake TR-7 to my solid state SPE Expert HF amplifier. My K3 had always played beautifully with the SPE as had  a number of other boatanchor rigs- both vacuum tube and solid state. I tried ALC, no ALC, all sorts of fixes. The issue turned out to be common mode on the PTT line from the rig to the amplifier. Who would have thunk it.

 

Dale W4OP

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Evan Hand
Sent: Thursday, June 18, 2020 8:45 AM
To: BITX20@groups.io
Subject: Re: [BITX20] RFI on 2 meters from uBitx

 

Dale's message prompted me to think of other cables that run near the Raduino.  By chance are you using CAT from the rig?   Snap a ferrite on it and any digital mode cables. 

Dale,
A good suggestion for the ferrites.  I already have them on my rigs because of RF feedback.

73
Evan
AC9TU


Evan Hand
 

I checked, and I do have the 2 meter signal of the SI5351 3rd harmonic.  It goes away on CW TX, confirming to me it is the LO Clock2 signal, as that is changed to the actual frequency on CW TX.

As Jay noted, it is quite strong.  My ubitx v4 has the relays replaced, and I have verified the harmonic reduction after the replacement.  It is in a metal case, however, I do not have a good ground in the shack, just a copper water pipe. If I use my hand as a temporary RF choke around the antenna coax, I can get a significant reduction in the signal strength on the Kenwood TM-D710G, the squelch will drop out.  Based on my simple test, ferrites on all lines into and out of the rig would be the answer.

Best guesses at this point.
73
Evan
AC9TU


Blobby Harvey
 

Hi Jay
I had the same problem RFI around 2m. I put the the bitx in a metal case and ferrite ringed the power lead. 

I had no more problems. 

73’s. Shane ZL2SH

On Fri, 19 Jun 2020 at 12:11 AM, Raj vu2zap <rajendrakumargg@...> wrote:
You could try replacing relays KT1/2/3 with Axicom RF relays, that should reduce this.
Check earlier posts for details.

Raj

At 18/06/2020, you wrote:
>I have been experiencing RFI on the 2 meter band when my V3 is tuned to the upper end of 75 meters. I had my uBitx tuned to the TN Phone net at 3.980 MHz and my 2 meter rig tuned to my local repeater at 146.91 MHz. The 2 meter rig showed full scale receive, with no audio. I checked with my hand held and it was full scale at least 50 feet from the uBitx. The RFI exists when the uBitx is in RX as well as TX. Seems like a 3rd harmonic of a mixing product; (45 MHz+3.98 MHz) X 3 = 146.94 MHz
>
>Any ideas where or how to add shielding or if a component needs to be replaced?
>
>Thanks,
>Jay
>WS4JM





MVS Sarma
 

Cool. Shane, concept appreciated. Congrats.

Sarma vu3zmv

On Fri, 19 Jun 2020, 5:58 am Blobby Harvey, <blobbyharvey4@...> wrote:
Hi Jay
I had the same problem RFI around 2m. I put the the bitx in a metal case and ferrite ringed the power lead. 

I had no more problems. 

73’s. Shane ZL2SH

On Fri, 19 Jun 2020 at 12:11 AM, Raj vu2zap <rajendrakumargg@...> wrote:
You could try replacing relays KT1/2/3 with Axicom RF relays, that should reduce this.
Check earlier posts for details.

Raj

At 18/06/2020, you wrote:
>I have been experiencing RFI on the 2 meter band when my V3 is tuned to the upper end of 75 meters. I had my uBitx tuned to the TN Phone net at 3.980 MHz and my 2 meter rig tuned to my local repeater at 146.91 MHz. The 2 meter rig showed full scale receive, with no audio. I checked with my hand held and it was full scale at least 50 feet from the uBitx. The RFI exists when the uBitx is in RX as well as TX. Seems like a 3rd harmonic of a mixing product; (45 MHz+3.98 MHz) X 3 = 146.94 MHz
>
>Any ideas where or how to add shielding or if a component needs to be replaced?
>
>Thanks,
>Jay
>WS4JM





Jay - WS4JM
 

Thanks Everyone! Some very good information and things to try.

I have already switched to the Axicom relays, I installed my ubitx in an old Cobra 148 CB case (metal).

I will try ferrites on all of the power leads and report back.

Thanks again

Jay
WS4JM


Jay - WS4JM
 

Update,

I put a couple small ferrites I brought home from work, and the interference was reduced markedly with 3 turns through the ferrites. I will have to add wire to the power leads to get a few more wraps and I believe that this should solve my issues. Thanks to everyone who offered advice, and I hope to catch you on the air. I try to be on 7.277 around sunset on Sunday evenings.

73 de WS4JM
Jay