Dirty antenna tuner bypass

[lipzapper]

First off - New member here. Glad to be part of the forum.

I've got a issue to which a resolution has been avoiding me...hoping you guys share some of your smarts.


I've got an MFJ 949E tuner that gives me high(er) SWR when set to bypass.

My antenna's native SWR (Vertical dipole made of 109" SS whips) is 1.4:1. Hooked directly from transmitter, with ~50ft of coax, to antenna gives me that 1.4 reading as expected.
Enter Tuner
When the tuner is in 'bypass' mode my SWRs are hovering ~2-2.3:1.
It appears my tuner has a dirty bypass circuit as I'd expect no (maybe only slight) change.

Fixable?
Is this simply a bad connection the bypass circuit?....assuming that activating bypass simply jumps the input and output connectors, avoiding other tuner circuitry.

thx!
=lz

[MDYoungblood]

Could be the contacts on the switches are bad, also the jumper you are using could be as well. Inside the tuner is a couple caps that may have gotten warm over the years, check them too. The antenna length sounds a little long, most get a good SWR reading with 106".

3's

Greg

[lipzapper]

thanks! - Yea, it's been like that since new with 0 hours on it. Actually, two had the same issue. After explaining it to the shop from which I bought it, they said "we'll send you a new one, send the old one back when you get it". Second one came in worse, so I kept the first.
lol

I trimmed the 108s" down to about ~106. The design I followed noted that it's a 70ohm (1/2wave vertical dipole) antenna so, the 1.3-1.4:1 is what is to be expected with straight thru 50ohm cable.

Antenna isn't the problem - it's the tuner bypass circuit.
I guess it's no huge deal as I just don't bypass - just wondering what it could be

thx!

=lz

[Bluerunner]

"I've got an MFJ 949E tuner that gives me high(er) SWR when set to bypass.

My antenna's native SWR (Vertical dipole made of 109" SS whips) is 1.4:1. Hooked directly from transmitter, with ~50ft of coax, to antenna gives me that 1.4:1 reading as expected."

What meter are you using to get the above reading? The (949E, the radios built in swr meter or some other swr meter)?

If are you using the 949E with the switch in TUNED position to read the 1.4 swr then it is tuning the antenna to give you the 1.4swr.

"When the tuner is in 'bypass' mode my SWRs are hovering ~2-2.3:1."

If the 949E is the only swr meter you are using, then the 2-2.3:1 swr in BYPASS is the antennas actual untuned SWR.

[lipzapper]

I understand the confusion but, the antenna's actual untuned SWR is 1.3:1.

They bypass circuit makes it worse.

Readings were made from multiple meters.

[lipzapper]

in that last post I noted 1.3 as my antennas native SWR...in others I mentioned 1.4 - it's between that depending on the meter.

the antenna design, when tuned, exhibits best case SWR @ 1.4:1.

all is good until it hits the tuner's bypass, then it jumps

[MDYoungblood]

The best way to check the tuner would be with a 50ohm dummy load, could be the meter is out of calibration. If you sent it back and got another had the same issues I would be on the phone with MFJ complaining about their quality control.
There is a chance the there is enough CMC being produced to cause the meter in the tuner to go squirrelly.
What brand meters are you using to compare with? Are you comparing with the tuner before or after the external SWR meter?
I've never heard the term "native SWR" until now , looked it up, sure enough it's a term used by hammie's.

3's

Greg

[lipzapper]

hahaha

'native' - i thought I had made it up....glad it made sense....and even more glad it's a real thing.


Yea, i guess it could just be a difference in the meters but, that's a reasonable delta between.
Ant -> radio (direct) - 1.4swr on radio's meter (LincolnII+)
Ant -> Newer Diamond (somehtin or other) -> radio - 1.3 on diamond
Ant -> MFJ in in bypass -> radio - over 2 on both MFJ and radio all day long

ya know, you get me to thinking....I should try the Diamond before the tuner (from the antenna's point of view) and see what I have there.

On power tests, I've noticed the MFJ's meter being more stingy than the Diamond...so, seeing the SWR result go the other way, led me to believe i may have an issue there. - wasn't sure if a dirty solder joint in that bypass circuit - or 'something' - could have that result....?
I'll have to crack 'er open and trace things down. -sry to digress but, seeing as SWR is reflected power, i figured i'd bring that up...

I've got one of those Dosy Test Center things on it's way so, power wise, i'll know if the MFJ is stingy, or the Diamond more generous - and it'll be my double check against the MFJ as far as SWR. We'll see who Dosy agrees with.
-just hate having so much crap inline...that doens't help things.

Yea, two in a row - unreal.
I hear it's hit or miss with MFJ so, i swang twice and got two misses.
Seeing as it's not a huge issue, I didn't care to swing again. Otherwise it works fine and I don't really use the bypass.

-just figured i'd hit the brain-trust here with it to see what might surface.

Thanks for your thought on this!
-appreciated.

=lz

[MDYoungblood]

I just looked up the MFJ-949E tuner and it has a built in dummy load, now for curiosity sake what does that read?

3's

Greg

[lipzapper]

1.2 bypassed into DL

Bypassed into coax 1 is where I get the issue

thx!