OPEN WIRE AND RFI***problem solved***

[KB5MD]

I recently built a balanced line tuner as described on this board with the 1/4 copper tubing and link coupling etc.
Using it with 600 ohm open wire line and it works great on 80 and 40 but on 160 the line  radiates rf which gets into the audio.
I know open wire line is not supposed to radiate but for the life of me I cannot find a way to prevent it from doing so on 160. Any thoughts anyone, remedies, etc?  The antenna is a 160 meter dipole.

[W2PFY]

How long is your open wire? Sounds like you may be at a voltage point on the feed line on 160.

[k4kyv]

Is the mid-tap of the coil or the capacitor frame on the tuner grounded?  It should be left floating, despite the circuits shown in some of the handbooks showing it grounded.  If it is grounded, you may be getting some common mode current, with the OWL acting like a vertical radiator working against ground. Leave it floating, and there is no ground connection for it to work against.

[flintstone mop]

I had a similar thing happen on 160M. It was the audio console I was using. The VU meters would read half scale while I transmitted. No audio from the microphone. I grounded the chassis of the console to the station ground and it went away.
And I have balanced 600 ohm feed and a floating tuner, balanced audio throughout the station. Just an ungrounded audio console. It has the accepted 3 prong plug/safety ground.
All of your radio equipment must be separately grounded to a central grounding block and connect to a ground rod.
Fred

[Jeff W9GY]

Yeh, I'm inclined to agree with Fred's thoughts.  Work the problem in the audio equipment, there's some susceptibility there that needs taken care of.  One fixed, the entire audio system will be in better shape.

[The Slab Bacon]

Or add or shorten the feedline. You may be hitting the feedline right on a current node.

[aa5wg]

Look out for this:

"When the total length from the transmitter to one end of the aerial is near a complete number of half-waves there is a tendency for the two halves to act in parallel like a "T" aerial.  This brings up a high impedance to earth at the pick-up coil, a condition which is just right for transference of considerable energy through a small stray capacity to some live part of the transmitter.  The result is that besides the desired equal and opposite currents in the two wires, there are two more in-phase currents flowing in the PARALLEL CIRCUIT, and these will cancel part of the balance current on one wire and augment it in the other.  The parallel current radiates, and the aerial system is completely upset.  This parallel circuit is equivalent to the "Phantom" circuit used in line telegraphy and telephony".

Reference: The Amateur Radio Handbook, Second Edition, RSGB, 1939, page 186.

I agree with Don, as a sound guide you should not ground the center of the output capacitor or center of output tank coil.  However, in this situation, if this advice is in practice, it may be worth trying this ground?  This could possibly change the electrical length of the antenna system just enough to help.  Don, what do you say?

And, as an experiment, disconnect the line from the coupler and tune it to resonance with low power, i.e. 5 watts or so.  Don.t change any settings of the coupler.  Reconnect the line, apply low power and see the change in the match.  Instead of changing the coupler settings add a shunt variable capacitor at the coupler line connection and adjust this shunt capacitor and see what happens to the match.  If needed remove the shunt variable capacitor and try a shunt variable inductor to achieve the match.  If very little shunt is used the the coupler most likely can handle the match without any shunt.

Try series tune with the coupler and compare this with parallel tune with the coupler.

Chuck

[W0BTU]

... I know open wire line is not supposed to radiate but ...

Open-wire line is not like coax, where (usually) the RF is all contained within the shield. Even if it's perfectly balanced, there's a field around it that extends for some distance away from the line.

How close is the line to your operating position? I always ran coax to the balanced tuner, which was always in my shack but several feet away from the operating position.

UPDATE: I also always used open-wire line with less than 2" spacing, usually closer to 1". My theory is that the field around the closer-spaced line doesn't extend out as far away as, say, 6" spacing. Also, close-spaced open-wire line is not as subject to imbalance from nearby objects.

[K5UJ]

Tell us more about the audio the RF is getting into.  Is it coming from an external audio amp used to drive a speaker on rx?  Or is it your own transmit audio?   If the latter tell us about that--are you running some kind of external processing chain, what's the cable between the boxes and/or into the rig--balanced or unbalanced; shielded?   Or mic right into the rig?

I just a few days ago dealt with a 160 m. RF problem here also.   I was FB on 75 and 40 but on 160 when running 300 w. I was getting distorted tx audio out of a speaker driven by my heathkit EA-2 amp.  It gets audio from a mixer board that comes in on a channel from the rx detector tap.  I wrapped the audio cable to the amp (just one of those shielded coaxial phono cables with one center conductor) at the EA-2 input around four split ferrite cores, 3 turns on each one and that fixed the problem.  On 160 I am using an inverted L fed with coax and unbalanced tuner but 160 m. RF affected the amp whereas the balanced line and Matchbox RF on 75 and 40 did not.   

If you get into using ferrite to fix the problem, find cores that have the most XL on 160.  You can do that by making a one turn loop through each core under test and using a MFJ SWR analyzer to measure the inductance on your operating frequency.  The 259 gives uH and reactance.

[k4kyv]

Look out for this:

"When the total length from the transmitter to one end of the aerial is near a complete number of half-waves there is a tendency for the two halves to act in parallel like a "T" aerial.  This brings up a high impedance to earth at the pick-up coil, a condition which is just right for transference of considerable energy through a small stray capacity to some live part of the transmitter.  The result is that besides the desired equal and opposite currents in the two wires, there are two more in-phase currents flowing in the PARALLEL CIRCUIT, and these will cancel part of the balance current on one wire and augment it in the other.  The parallel current radiates, and the aerial system is completely upset.  This parallel circuit is equivalent to the "Phantom" circuit used in line telegraphy and telephony".

Reference: The Amateur Radio Handbook, Second Edition, RSGB, 1939, page 186.

I agree with Don, as a sound guide you should not ground the center of the output capacitor or center of output tank coil.  However, in this situation, if this advice is in practice, it may be worth trying this ground?  This could possibly change the electrical length of the antenna system just enough to help.  Don, what do you say?

I agree.  That would be a special case where the mid-tap of the coil or the split stator frame should be well grounded, so perhaps I need to modify my statement that the tuner should always be left floating. What they call "parallel currents" is also known as "common mode" currents in more modern day terminology, and less confusing.  Say you have 3 amps in each conductor at some point in the feed line, but due to the Tee Antenna effect (ungrounded tuner) or Marconi Antenna  effect (grounded tuner) there is an additional amp of common mode current in each conductor, an rf ammeter inserted at that point will read 4 amps in one feeder and 2 amps in the other, if the common mode and differential currents (the desired current) are exactly in phase. Common mode current on the feed line, whether OWL or the outer conductor of coax, may (most likely will) cause rf in the shack and feedline radiation.

As I mentioned to Rob when were discussing the topic regarding the Johnson Matchbox, a heavy conductor connected to the frame of the split stator capacitor should be run to a two-terminal connector at the rear of the box, which could be strapped to ground or left floating, depending on what works best.  Maybe there should even be a switch on the front panel, since some configurations might work best with the capacitor floating on some bands, and grounded on others. The ultimate test is to place a pair of thermocouple rf ammeters in series with each conductor of the OWL and check for balance.

[ke7trp]

I would need pictures of your tuner and a diagram to really see how this thing is built and or wired.

My guess is your lines are not ballenced on 160.  Its really a must to have some indication of the current on each wire.  Light bulbs or current meters.  You will see that a SLIGHT mistune of the coupler will cause a big inballance and then a major radiation of RF off the line.   

Its also nice to have a field strengh meter handy. You can place this around the tuner, coax shield and in the NULL of the OWL at low power to check balance and common mode.

The other big plus of the current meters, is the fact that you can tune the coupler for max output current.  The ratio of cap to coil is really critical here. without current meters, You cant find that sweet spot.

Look up kc6mcw on qrz.com   There is a diagram showing exactly what Don was suggesting about the ungrounding the coil and the current flow.

C

[KB5MD]

Moved the feed line, shortened the feed line, and relocated the tuner, all for nothing.  Problem was solved by rerouting an audio line inside the transmitter cabinet.  Thanks for all the help and suggestions. 

[K5UJ]

Look out for this:

"When the total length from the transmitter to one end of the aerial is near a complete number of half-waves there is a tendency for the two halves to act in parallel like a "T" aerial.  This brings up a high impedance to earth at the pick-up coil, a condition which is just right for transference of considerable energy through a small stray capacity to some live part of the transmitter.  The result is that besides the desired equal and opposite currents in the two wires, there are two more in-phase currents flowing in the PARALLEL CIRCUIT, and these will cancel part of the balance current on one wire and augment it in the other.  The parallel current radiates, and the aerial system is completely upset.  This parallel circuit is equivalent to the "Phantom" circuit used in line telegraphy and telephony".

Reference: The Amateur Radio Handbook, Second Edition, RSGB, 1939, page 186.

Well jeepers, if you go by the "magic" odd multiple of 1/8th wave at your lowest operating frequency rule for the feedline length, you are probably going to wind up with a total length on each side that is "near a complete number of half waves."  on 80 m. 1/8 w. is 32 or 33 feet.  Well 1/8 w. feedline length is pretty much out unless you want an dipole up 10 feet, so next is ~ 100 feet.  Well, if you do that and add the length of one side of the dipole, 65 feet you wind up with around 170 feet total, near 3 half waves at around 180 feet.   Probably if not on 80 then on one of the higher bands.

As I mentioned to Rob when were discussing the topic regarding the Johnson Matchbox, a heavy conductor connected to the frame of the split stator capacitor should be run to a two-terminal connector at the rear of the box, which could be strapped to ground or left floating, depending on what works best.  Maybe there should even be a switch on the front panel, since some configurations might work best with the capacitor floating on some bands, and grounded on others. The ultimate test is to place a pair of thermocouple rf ammeters in series with each conductor of the OWL and check for balance.

Easy to add the ground - no ground knife switch to the back of the MB; hard to come up with a permanently in-line or some other indicator as to which position the switch should be in.   If you go the amp meter in line route you have to throw a carrier to the antenna every time you want to check--not always an option with a busy frequency.  You can QSY to a clear frequency but we get to the point where the hassle factor may start to be greater than the potential benefit.  Also, the line can look balanced at the back of the tuner but if you insert amp meters farther out along the line the balance has changed.  The readings depend on where the meters are in the line.   I saw no difference in balance (after I corrected an interaction problem that was unbalancing the line which gave me a false notion that floating the caps was better) between grounding and floating the caps in the Matchbox--the line was around 10% unbalanced either way; 2nd harmonic attenuation with the caps grounded was about 5% better compared to having them float which is not significant (within margin for error).*   I tried both ways this morning on 75 m. and no major difference in signal strength was noted.   A real test though would be with local field strength measurements.  It seems the major difference if any is with common mode RFI and I'm not aware of any either way here so I don't know how to test for that, so I decided to go back to the stock Matchbox.

Rob

*The measurement was made by tuning the MB to the fundamental, feeding 2nd harmonic frequency RF through it and measuring the signal strength with the capacitors grounded and floating.  Grounded = 45 dB; floating = 48 dB.  According to the 1941 West Coast Handbook (Radio Handbook Editors and Engineers) a CT on the inductor grounded prevents capacitive coupling and attenuates 2nd harmonic--it is my understanding that grounding the caps is equivalent to a grounded CT. 

[ke7trp]

Being surounded by 7 neighbors in close proximity, and a sprinkling of other hams, one is 500 yards away with a tower and beam, Forces me to keep my signal Spotless and clean from the audio rack to the antenna.  If you live in a wide open space, this no longer matters and you can just LET IT RIDE and pay no attention to your signal quality.


The link coupled tuner design here works but is not optimal.  Its a very old design In its current form, It has harmonic suppression of about 18 to 20 db.  At least mine did. By fooling around with it and testing different input designs, I got this down to 45 to 50. Alot of the issues with the neighbors went away.  The hams on 40 that where under a mile from me can no longer hear me on 75.   

Do not forget to add the Choke from center of coax input to ground. This cure alot of RFI issues and stop the Common mode cold. 

In the end, I wonder if all of this was worth it.  A simple Coax fed dipole with two wires for 80 and two for 40 will pretty much beat this setup and you wont need the big tuner taking up desk space.





C

[Steve - K4HX]

The on air performance will be the same but it sure is simpler. It  is what I used for quite a few years. To me it makes the most sense if you have other antennas for the higher bands and/or have another antenna for 160 or aren't interested in operating on 160 meters.

A simple Coax fed dipole with two wires for 80 and two for 40 will pretty much beat this setup and you wont need the big tuner taking up desk space.

[ke7trp]

Agreed. The moment you are not going to use one wire antenna for all your bands, Then just use resonant coax dipole's.  My beam is going up soon and I have a real nice L for 160.  No need to have that line and the open tuners here in the shack.

C

[Steve - K4HX]

Sweet! You're set.

[K1JJ]

Umm... bear in mind that a coax-fed two band dipole (legs for both bands) has ZERO db of second harmonic attenuation, assuming the two bands are X2 related, as most ham bands are.

If someone is already having problems with second harmonics due to a transmitter that has less than -40db of FCC required attenuation, then the two band dipole will be worse than a link coupled tuner that supposedly has only 18-20db of second harmonic attenuation.

The link coupled tuner is a FB and simple design for most applications.


(Finally have power and cable back after a week down!)

T

[ke7trp]

I did not think about that    I will probably bother the old fart a mile away on 40 again.  He wont get rid of that damn 430 kenwood and complains if he hears anything other then the liberty group. 

Dont discount someone elses measurements like that. Do your own work and provide data, Otherwise, Its just Band noise on the internet 

You dont even run that tuner and likely have never tested it like both of us here that have built it, run it, tested it and then had to fix it.  Its not productive for anyone of us to argue and poke each other.



C

[Steve - K4HX]

You could build a 50 Ohm lowpass filter (cut-off at 4 MHz) and fix any problems with the 2-band coax dipole.

I didn't understand the rest of your post.

[ke7trp]

I think its easier to give the old fart a decent radio.  His 430 died and he borrowed a friends Yaesu and never heard me for the 2 weeks it took to get the 430 fixed. Then like clock work started to complain to me when he got the 430 back inline.  1 mile,FB AM = torn up Front end of 430.  I really just want to simplify my Tower and station here. I am never going to use that wire higher then 40 when the beam is up.

C

[K1JJ]

You dont even run that tuner and likely have never tested it like both of us here that have built it, run it, tested it and then had to fix it.  Its not productive for anyone of us to argue and poke each other.

There you go again. Where did you get that idea, OM? I ran five of those tuners, all on the same table, at one time. I've used them on 20, 40, 75 and 160M. Never had a problem.  Finally went back to all coax-fed and hardline antennas for the simplicity.

BTW, glad to hear the RFI antenna tuner problems you were having with your neighbor were finally solved when the cable company discovered rusted connections and bad cables next door. At least that's what I read you posted on another site. It would have been nice if you followed up last time and mentioned it here after the last rukus.

So are we ready for round two or shall we call it a truce?

T

[flintstone mop]

Very good post Tom,
My antenna system/tuner is setup for 40M (7MHZ) now. I cannot show a resonance with my MFJ259 on the 2nd or 3rd harmonic.

My 40M vertical out back will take RF from the MFJ and show resonance on the 2nd and 3rd harmonic of 7 mhz.

Roy, Glad to read a simple re-arranging of an audio cable fixed your problem
Clark, ask your complaining Ham friend to turn on the attenuator on the front end of his radio. His radio probably has a barn yard door front-end.....fundamental overload
Fred

[ke7trp]

Tom, That neighbor with bad cable and cable preamp could hear the icom at 10 watts on just about any band.

The point that you keep skirting is that the tuner in its original 1930s form offers alot less rejection. The KW I have for comparison was much much cleaner on the bands.

After trying every possible version out of handbooks, i found one that knocked the second harmonic down to 45 to 50 DB.  This stopped most of the complaints.   

So another member comes along and has the exact same issue and on his own solved the issue the exact same way I and you make sly comments that you dont believe the 18 to 20 db figure.

I think that you attached your name to a tuner that is really a poor performing design and because your name is on it, you really take offense to any problems with it.  Out of respect, I never use your call sign anywhere when discussing it (go back and look).  I think if you had the tuner there with an antenna you would have tested some other designs and found the same thing both of us have!

 I really dont want to argue.  I have 100% no issue with you either way man.

[Steve - K4HX]

Funny stuff Clark. The design is so poor that it has been used effectively by hundreds and thousands of hams for decades and been included in almost every handbook printed in the last 70 years. But YOU know better. And you expect us to believe this on purely anectdotal evidence. Gives us all a break. You serve no useful purpose by making claims not backed up by any legitimate measurements. This is the tech section, not the Clark has a bone to pick with Tom section. Take it elsewhere.