AM Transmission coming over receiver speaker

[KC3GMQ]

Yes,  This has been addressed quit a few times I see,  but the closest article I have found was one on the HT-37.  So hopefully I am just blind and not too dumb.  I was going to reply to the other thread,  but the forum said it was an old one and maybe I should ask in a new one...soooo  here I am.

  So I am using a Viking II, with a Hammarlund HQ-180 (not an A).  I built my transfer switch just like the one mentioned in the (HT-37 thread on this subject).  The Hammarlund book is pretty vague, it just says to connect to the muting plug on the back (duh).  Anyway, my switch works, it mutes the receiver (S-Meter shows a drop like if I turned my RF gain off) but I still get my transmissions on my speaker???  I tired a different receiver also, (Hammarlund HQ-100A)  It is not as bad but still getting my transmissions from the Viking out of the speaker.  Do I need to add the speaker to the switch to have it grounded during transmission?  Or is the Hammarlund not really muting very well? ( I have read a few article that claim Hammarlunds have poor muting?)

Hammarlund HQ-180 has the 2 spade plug for muting,  NOT the octal plug the A has.

Replies a 5 year old would understand please

Dave
KC3GMQ

[k7mdo]

I have similar setup with no issues but assume your transfer switch includes antenna changeover relay as well as receiver mute function.  I didn't go back to HT-37 article so not certain of that.

If all of above is as it should be, I would start checking for RF in the shack from the antenna feedline but I imagine you have thought of that.

Changeover relay all in a metal box?..... 

Just first thoughts...

73, Tom

[KA2DZT]

Muting is usually done by cutting off B+ to some of the circuits in the receiver.  You should not be hearing you audio coming out of the speaker.  I suspect it is something with your interconnecting wires or grounds.

You might have some serious RF in the shack,  Check your coax connections making sure all the shield connections are good.

Fred

[KC3GMQ]

It is an all metal box, and I will recheck my grounds.   The relay swaps the antenna between TX and Rec. also has a strip with contacts for the muting NC, No and Grd. I do not have the transfer switch grounded, maybe it should be

[kb3ouk]

I'm assuming you are using the same speaker on both receivers? Is the sound coming from the speaker itself and not like it is being amplified by the receiver? Sounds like an issue I have here on certain bands when I run enough power, the speaker acts as a detector and the modulation comes out through the speaker. Not sure how well it would work, but you could try winding the speaker wire through a toroid or put a ferrite bead or two on the line and see if that helps. I thought about trying that here but haven't got around to it.

Shelby

[KC3GMQ]

Yes same speaker, Hammarlund. That's worth a try also. However I don't want to use a bandaid, if there is a real issue that should be resolved.

[steve_qix]

I took a *quick* (very quick) look at the schematic for the HQ180.  It appears as if the mute leaves the audio circuits intact and operational.

So, the question is:  how "loud" is the audio coming from the speaker when you transmit?  What does it sound like?  Does the receiver otherwise mute (no S meter response, tuning the receiver does not affect the audio from the speaker, etc. etc.)?

It could be RF getting into the receiver audio circuits...which means you may have some RF in the shack, so to speak.

You could try something like a .1uF cap from the speaker output on the back of the receiver to ground... if that stops it or reduces it, that will tell you something anyway.

[kb3ouk]

In my case, I believe the speaker wire is the antenna and something inside the radio is rectifying the RF and making audio. Proximity to the antenna makes a difference, my issue only occurs on 40 meters on an antenna that's closest point is in a tree about 10 feet from the shack. This was on an icom 718 and when you keyed up to talk, you heard your own RF in the speaker, I never have the issue with the internal speaker so that's why I think at least in my case the ferrite on the speaker wires would reduce our eliminate the RF entering the receiver through the speaker wires.

[KC3GMQ]

So, the question is:  how "loud" is the audio coming from the speaker when you transmit?  What does it sound like?  Does the receiver otherwise mute (no S meter response, tuning the receiver does not affect the audio from the speaker, etc. etc.)?

The S meter goes dead (good thing) But I get nice clean audio of me transmitting lol, and the volume is proportional to where the volume knob is.  I have been turning it down to Zero.  I will try the cap idea first.

[KA2DZT]

Try putting by-pass caps (.01 to chassis ground)(one on each wire) on the muting wires at the receiver.  The RF is probably riding back into the receiver on those wires.  The volume control has an affect on the level, so that tells you it's being detected somehow at the volume control or some circuit ahead of the control.

Fred

[KC3GMQ]

ON  So I took to orange drops .01 and soldered one to each of the leads to the T/R mute switch (where it plugs into receiver) and then ran caps to chassis ground.  It worked about 90%, still have a bit of speech in there, but it is garbled now (not crystal clear) and at lower volume levels its hardly noticeable.  Is this success? Well its a ton better, but I would like to resolve it completely. Should I add caps to the speaker wire?  Should I redesign how the receiver mutes?  Is what I have done a good fix, or a band aid?

[KA2DZT]

ON  So I took to orange drops .01 and soldered one to each of the leads to the T/R mute switch (where it plugs into receiver) and then ran caps to chassis ground.  It worked about 90%, still have a bit of speech in there, but it is garbled now (not crystal clear) and at lower volume levels its hardly noticeable.  Is this success? Well its a ton better, but I would like to resolve it completely. Should I add caps to the speaker wire?  Should I redesign how the receiver mutes?  Is what I have done a good fix, or a band aid?

You may want to try .01 disc ceramic caps.  If the orange drops are a form of rolled foil cap they may have too much inductance.  Always by-pass with disc ceramic caps.

Second post today about folks using orange drops where disc ceramics are needed.

Fred

[KC3GMQ]

Yes I expected that I guess. I had orange drops, browns and tubular but no discs lol. I will get some ordered . Thank you

Dave
KC3GMQ

[ka1tdq]

I have an open-frame 1500 watt transmitter sitting on my operating desk. I'm probably about the worst case scenario for "RF in the shack." Every time I get an RFI issue, I put either a snap on choke around it or wrap the wire around a ferrite core. I'm too scared to count how many cores I have installed, but everything works great! I'm sure that I'm exceeding the FCC safety limit for RF exposure when I transmit.

Maybe you could put 3 cores on the speaker wires.  One on each end and one in the middle.

Just my 2 cents.

Jon

[n2bc]

Lets go back to your T/R relay setup.   Is the main antenna relay switching single pole or double pole?

With a two pole relay for the antenna switching, pole one handles switching the antenna between TX and RX.  The second pole grounds the RX antenna line when in transmit.   (*)

Now, adding one or two smaller and faster DPDT relays into the mix will give you 2 or 4 additional double throw pairs. Use one for RX muting, use another directly on the RX speaker line to open it and add a 10 ohm load for the RX speaker line when in transmit. 

(*) Working with 50 year old tube transmitters, it is a good idea to add an additional safety RF choke across the TX RF input to the TR switch.

Be careful in there.   73,  Bill  N2BC