MFJ coaxial antenna switch issue.

[AC9KH]

My tuner is internal of the Yaesu FT991A.

I gathered that was the case. In situations where a radio might have dual antenna outputs, or a tuner has dual or triple outputs, IMO that is a better choice for switching antennas than coax switches.

One application where coax switches are nice is if you have two radios and only one external tuner, you can use the switch to switch between radios. But, again, DO NOT use those MFJ grounding switches for that. It will connect the center conductor of one radio to the RF ground system on the other and blow the front end out of it.

You might ask me how I know.

I once had this idea that I could use one of those MFJ grounding switches to switch from my radio to my antenna analyzer, use the analyzer to tune the antenna with the manual roller inductor tuner, then switch back to the radio and I'm all tuned up and ready to run. It was an excellent idea, no long tuning carriers on the air trying to tweak the roller inductor and twin capacitors in the tuner. Except for one problem. When I keyed the transmitter it blew that antenna analyzer all to smithereens and it was non-functional after that. That was the point where I decided the anvil and maul thing was the best fix for those MFJ grounding switches.

 

[kb1fua]

I gathered that was the case. In situations where a radio might have dual antenna outputs, or a tuner has dual or triple outputs, IMO that is a better choice for switching antennas than coax switches.

One application where coax switches are nice is if you have two radios and only one external tuner, you can use the switch to switch between radios. But, again, DO NOT use those MFJ grounding switches for that. It will connect the center conductor of one radio to the RF ground system on the other and blow the front end out of it.

You might ask me how I know.

I once had this idea that I could use one of those MFJ grounding switches to switch from my radio to my antenna analyzer, use the analyzer to tune the antenna with the manual roller inductor tuner, then switch back to the radio and I'm all tuned up and ready to run. It was an excellent idea, no long tuning carriers on the air trying to tweak the roller inductor and twin capacitors in the tuner. Except for one problem. When I keyed the transmitter it blew that antenna analyzer all to smithereens and it was non-functional after that. That was the point where I decided the anvil and maul thing was the best fix for those MFJ grounding switches.

Thanks for the input, and advice...
Sometimes...acrually most times, others experience is worth listening to.

 

[MIMTBR]

So, depending on which MFJ switch you got, some of them connect the radiating element to the ground, which combines it with the RF grounds on all your antennas together. The ones with so-called built-in "lightning protection" do this. This totally affects the tuning of your antennas, because as I'm sure you're aware the RF ground is an integral part of the RF AC circuit. You're not only trying to tune the antenna you're connected to, it's also trying to tune the other shorted out antenna(s) that are also in the circuit.

Would this apply to other brands of switches that ground the unused ports, ie Alpha Delta, Diawa...?
I've not heard of this problem with any other brand of switch.
Is there a unique design to these MFJ switches that cause problems?

 

[kb1fua]

Would this apply to other brands of switches that ground the unused ports, ie Alpha Delta, Diawa...?
I've not heard of this problem with any other brand of switch.
Is there a unique design to these MFJ switches that cause problems?

I didn't with my DX Engineering switch. Unfortunately I didn't have it.
After the issue with these, I bought 2 Alpha Deltas (I couldn't get the DX ones as quick, and these cc were recommended)I received them today. I will be putting one online and testing tomorrow.

 

[AC9KH]

Would this apply to other brands of switches that ground the unused ports, ie Alpha Delta, Diawa...?
I've not heard of this problem with any other brand of switch.
Is there a unique design to these MFJ switches that cause problems?

I'm not actually sure about other brands of switches. I've only had a MFJ switch apart because I had the same problem that KB1FUA had. I am still using one of those switches, however. I have it between my transmitter and tuner and use it to switch from the tuner to my dummy load. In that application it doesn't cause any problems.

 

[kb1fua]

I put the Alpha Delta switch inline, and all works good now!
Amazing what a difference a $20 bill makes...😑

 

[AC9KH]

I put the Alpha Delta switch inline, and all works good now!
Amazing what a difference a $20 bill makes...😑

That is excellent! I suspect the other brands of switches must use a different isolation scheme, like maybe diodes or something.

But still, swapping the switch out with another brand that works pretty much reinforces my theory that MFJ just wasn't thinking about what they were doing when they designed those "lightning protection" switches. I suspect it looked good on paper but they never thought about some antenna combinations where loading up the active radiating element as an electrical part of the groundplane of another antenna on the switch just doesn't work. If you have non-resonant antennas that you always use the tuner on, you may never notice it. But if you have resonant antennas that don't require the tuner, their switching and grounding method screws up the SWR on your resonant antenna by putting the other antenna(s) on the switch into the circuit as reactive impedance.

So I maintain that it was simply a bad design on MFJ's part. However, they also made coax switches without grounding "lightning protection" and those switches work fine. The 1702C, for example, is a grounding 2-port switch. The regular 1702 is a 2-port switch that just switches the center conductor. If you had the 1702 vs the 1702C, the 1702 wouldn't cause this problem.

 

[kb1fua]

That is excellent! I suspect the other brands of switches must use a different isolation scheme, like maybe diodes or something.

But still, swapping the switch out with another brand that works pretty much reinforces my theory that MFJ just wasn't thinking about what they were doing when they designed those "lightning protection" switches. I suspect it looked good on paper but they never thought about some antenna combinations where loading up the active radiating element as an electrical part of the groundplane of another antenna on the switch just doesn't work. If you have non-resonant antennas that you always use the tuner on, you may never notice it. But if you have resonant antennas that don't require the tuner, their switching and grounding method screws up the SWR on your resonant antenna by putting the other antenna(s) on the switch into the circuit as reactive impedance.

So I maintain that it was simply a bad design on MFJ's part. However, they also made coax switches without grounding "lightning protection" and those switches work fine. The 1702C, for example, is a grounding 2-port switch. The regular 1702 is a 2-port switch that just switches the center conductor. If you had the 1702 vs the 1702C, the 1702 wouldn't cause this problem.

I Agree.
Weird, and wild.
MFJ has had some good stuff...been a few years tho, but for the most part it's why it's called "mighty fine junk" .

 

[AC9KH]

I Agree.
Weird, and wild.
MFJ has had some good stuff...been a few years tho, but for the most part it's why it's called "mighty fine junk" .

I can't really fault MFJ. I've had a lot of their stuff that I've been very happy with. The stuff they built is usually user-serviceable, they supplied all the schematics for it, and they even encouraged the amateur to try to fix it him/herself under warranty before sending it in, and they didn't void the warranty if you screwed it up.

That's not saying that all their stuff was perfect. Like their roller inductor tuners with that anti-resonance bar in it. Another thing that probably looked good on paper, but it was a disaster in actual operation. So buy a brand new one and the first thing I did was tear it apart and remove that stupid anti-resonance thing from it and it worked fine.

They will be missed - especially in tuners and amplifiers where they built a lot of pretty good stuff at a reasonable price.

 

[kb1fua]

I can't really fault MFJ. I've had a lot of their stuff that I've been very happy with. The stuff they built is usually user-serviceable, they supplied all the schematics for it, and they even encouraged the amateur to try to fix it him/herself under warranty before sending it in, and they didn't void the warranty if you screwed it up.

That's not saying that all their stuff was perfect. Like their roller inductor tuners with that anti-resonance bar in it. Another thing that probably looked good on paper, but it was a disaster in actual operation. So buy a brand new one and the first thing I did was tear it apart and remove that stupid anti-resonance thing from it and it worked fine.

They will be missed - especially in tuners and amplifiers where they built a lot of pretty good stuff at a reasonable price.

Yes sir...
I have had a few of their newer tuners, and had little to no issues. Likewise with many of their antennas. They had nice prices on them too.
I Agree they will be missed.

 

[AC9KH]

I have had a few of their newer tuners, and had little to no issues.

Yep, I got a 993B on my IC-7300. I love that tuner, it's one of the best auto-tuners I've ever had and it interfaces with the 7300 flawlessly. The 7300 has its internal tuner, but the 993B will load up a rusty pole barn spike on 160, the internal tuner in the radio just don't have that capability.

 

[kb1fua]

Yep, I got a 993B on my IC-7300. I love that tuner, it's one of the best auto-tuners I've ever had and it interfaces with the 7300 flawlessly. The 7300 has its internal tuner, but the 993B will load up a rusty pole barn spike on 160, the internal tuner in the radio just don't have that capability.

The only external tuner I got left is a homebrew roller I built back in 2009. And it it tuned some pretty weird stuff, ha ha.
I just had a hard time getting rid of it. The others I had donated to new hams, or a club that needed it.
I once tuned a plastic covered steel cable clothesline for 40m. It was on the fringe, but it was acceptable.