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[Articles Home]  [Add Article]  

Nip RF Feedback Before It Nips You!

Edward P. Swynar (VE3CUI) on November 24, 2016
View comments about this article!

Don't Let RF Feedback Spoil Your Portable Operations!

Have you ever experienced the unpleasant surprise of a sudden "...lip-biting microphone" during any course of your on-the-air transmissions? How about unsolicited remarks from Hams you might be working, who claim that your SSB signal is plagued with distortion caused by RF feedback? Maybe the settings of the controls on your external antenna tuner are very critical and otherwise "touchy" on some bands, and that they "...just act wonky," as you attempt to make adjustments? Does this sound at all like the situation in YOUR station?

If so, then welcome to my world! These were my "realities" this past summer as I endeavored to put VE3XZ/3 on the air from our modest lakefront cottage in eastern Ontario -- and I'm sure that my experiences are not all that isolated, or rare, either...and NO, the solution is NOT to simply avoid those specific bands giving you problems and staying off the air, either!

My set-up there consists of a 30 year old Yaesu FT-980 transceiver (100-watts output), which is situated on the first floor of our summer getaway: just above it, some 15-feet, or so, to the south -- and lashed to the wooden balcony railing on the second story -- is my homebrewed 20-, 15-, and 10-meter seasonal ground plane antenna. This aerial consists of nothing more elaborate than a vertically oriented 1/4-wave (on 20-meters) aluminum pole, which is affixed (by way of three bungee-cords) to a wooden corner post of the guardrail: separate 1/4-wave insulated wires for 15- and 10-meters are taped to its side, and the bases of these wires are all bonded together at the bottom of the pipe, which serves as a common feed point for this ad hoc "tri-bander." The center pin of a run of RG-58 coaxial cable feeder from the rig is affixed to this point.

The ground plane has two counterpoise wire elements per band, which consist of nothing more elaborate than 1/4-wavelength sections of insulated wire taped together, bonded at one end to the coaxial braid, and snaked in near-opposite directions between the wooden support posts to reduce their invasive presence to non-Ham frequenters of the balcony.

I was experiencing some truly "...wild and crazy" occurrences whenever I would attempt to tune my antenna on 10-meters: in addition, my mic would occasionally "nip" me on 20-meters, and I was concerned about comments regarding the "...RF on your audio, OM" that some Amateurs made note of to me (operation on 15-meters, however, was pretty much "text book" both in execution and nature). Obviously, my set-up was prone to experiencing some sort of a ground loop that was plaguing my enjoyment of the HF bands, no doubt due to the orientation of, and the close proximity between, my antenna and my operating position. Whenever I would reduce my power to some 30-watts of output, or so, these issues would disappear -- but why limit one's self to such low power levels, when the '980 just loafs along at its prescribed 100-watts?

My solution was two-fold: first, in order to eliminate/minimize any sort of feedback to the transceiver that arrived to it by way of the feeder, I contrived an easy-to-replicate common mode suppression choke (see attached): this choke consists of nothing more elaborate than 21 close-wound turns of coaxial cable that is threaded, toroid-style, about a common, ordinary cathode ray tube (CRT) deflection yoke salvaged from an old television set. You've seen these many times before, I am sure: they are attached right at the tapered end of the picture tube that projects your television/computer monitor image to the opposite front of the screen -- it's that intimidating-looking "thing-a-ma-jig" that is all wrapped-up in many layers of enameled copper wire. Remove this deflection yoke (power disconnected to the outfit that you might be cannibalizing FIRST, of course!), peel off the wires, and VOILA! You have the foundation for a wonderful common mode RF feedback suppressor...and best of all, it's FREE (and remember here to pat yourself on the back, too, for re-cycling a piece of some electronics stuff and keeping it out of your local landfill site!)

There is nothing at all critical about the construction of one of these: simply scrounge-up the largest ferrite core that you can, and start winding, getting as many turns onto it as you can -- again, it is not especially vital that you duplicate, precisely, my particular effort. Just be careful not to over-lap the "entrance" and the "exit" points of the wires on the ferrite, or otherwise bring them into too close a proximity to one another, which might defeat the whole purpose of "isolation." My core had an overall outside diameter of some 4", and an inside opening of 3-3/4" at its widest point, and 1-3/4" at its narrowest (the core is "funnel" shaped, or tapered, and is some 1-3/4" in overall height). I first wrapped the entire "donut" with a layer of masking tape to guard against the possibility of any sharp nicks in it from piercing the cable: the turns were secured to it with two plastic tie straps, and the ends of the coaxial cable were dressed with standard-issue PL-259 plugs (using suitable reducers) -- a double-female connector is installed at one end.

You may have to experiment at this point to see where placement of the choke might be most effective in your particular set-up. In my instance, I found that on 20-meters it worked best by being inserted right between the end of the antenna feed line and the antenna input to my transmatch: by contrast, on 10-meters, it worked best when installed between the tuner and the transceiver, itself. Why? I admit to my having no idea -- only that by my doing so, it eliminated the tuning issues that I had been experiencing before.

One caveat bears insertion here: if you find that, on a band like 15-meters you are not experiencing any RF problems -- as was the case here -- remove it completely from your system! At one point I neglected to do that, and the transmatch would not allow me to properly tune the antenna on 21-MHz -- again, for reasons unknown...but a lesson learned, none-the-less.

This solution "cured" the bulk of my RF feedback/tuning issues -- but there was still a trace of RF making its presence known on my 20-meters SSB signal. I surmised that the coiled mic cord to the rig was somehow creating a ground loop in and of itself, so I effectively "shorted" it. How? By the attachment of a simple alligator-clipped short jumper wire that directly connects a metal portion of my standard-issue Yaesu MD-1 desk microphone, to a grounded metal portion of the rig (see photo attached). Problem solved! I can now operate on any HF band, and in any mode, too -- just as long as I might remember to take these simple precautions in advance of my making any "CQ" calls.

These are, admittedly, crude ways to resolve what otherwise may well be complex issues -- but who really cares? THEY WORK FOR ME! And they may well work for YOU, too, and serve to merely enhance the personal enjoyment of your summertime retreat, wherever it may be. Try one, and/or both, if you've already attempted most everything else that you might think of -- be prepared to be very pleasantly surprised!

Photographs Attached:

Image #1 -- The base of my tri-band ground plane vertical showing its attachment to a corner post of the second story balcony of the cottage with three bungee cords, as well as the two counterpoise wires snaked between the vertical posts going away from the base in near-opposite directions

Image #2 -- A view of my common mode suppressor choke, showing details of its construction The initial protective wrap of masking tape, the plastic tie wraps that secure the wire, and the common PL-259 UHF-style end connectors, one of which is connected to a double-female UHF connector for insertion between my antenna tune and the feedline, for operation on 20-meters.

Image #3 -- My method of effectively "shorting-out" any ground loop caused by the long, coiled MD-1 microphone cord, to the FT-980 transceiver itself, i.e. simply a short jumper wire connecting the metal portion of the mic, to the rig's ground.

~73!~ de Edward “Eddy” Swynar VE3CUI -- VE3XZ

Member Comments:
This article has expired. No more comments may be added.
 
Nip RF Feedback Before It Nips You!  
by N1FM on November 24, 2016 Mail this to a friend!


http://www.w8ji.com/rfi_rf_grounding.htm

http://www.w8ji.com/second_floor_grounding.htm

 
RE: Nip RF Feedback Before It Nips You!  
by K6AER on November 24, 2016 Mail this to a friend!
Oh boy...where do we start.

A deflection yoke from a TV is nothing but a ball of wire. It is not a toroid. Your yoke will form a choke of sorts but the copper wire in the yoke is also a capacitance conductor of RF and probably negates any inductance value of the coax turns. The problem with RF on the microphone is the antenna field is too close to the radio and microphone. Several turns of microphone cord through a toroid type 43 mix will help the RF from getting into the audio input of the microphone. A .01 cap across the microphone input would also work very well.

The reason you are getting bit on the microphone is the radio and microphone is part of the antenna counterpoise. Your antenna needs a better counter poise system. Possibly 16 feet of wire draped over the balcony and attached to the antenna base ground might help. A good rule of thumb is for the antenna to be as many meters from the radio as the band of operation.
 
K6AER  
by VE3CUI on November 24, 2016 Mail this to a friend!
Well, WHATEVER it was that cured my ails, IT WORKED FOR ME…and it was simple, easy to do, and may be readily duplicated by others, as well…especially by those Amateurs who maybe don't feel exactly at home with a soldering iron, or are lacking somehow in their knowledge & ability of applying theory to practical real world situations.

I admitted, right in the body of the essay, that I do NOT exactly know how, or why, the fixes were so effective --- just as I readily confess that I have only the vaguest of understanding of the intricacies of the internal combustion gasoline engine…

Yet that HARDLY prevents me from climbing into the family chariot to run daily errands, or to go out for an enjoyable Sunday drive. I merely turn the ignition key, and VOILA! I'm on my way, with no questions asked, & no complications added to the exercise, whatsoever…

Ditto this write-up, IMHO…no matter, however: LET THE FLAMING COMMENCE, UNRESTRAINED…!
 
RE: K6AER  
by AA4PB on November 24, 2016 Mail this to a friend!
I have wrapped turns of coax cable around the core of an old TV yoke to prevent common mode currents from flowing on the TV antenna coax and getting into the set. It worked great.

As the OP said, you first remove all of the original wire so that you have just the magnetic core to work with. You can get quite a few turns of RG59 (for a TV set) on the core. A real toroid may be more effective for higher frequencies (i.e. 2M & 6M), but the free yoke core works fine for the HF bands.

 
RE: K6AER  
by K1PJR on November 24, 2016 Mail this to a friend!
I wouldn't worry about any flaming. You fixed your issues. Maybe not technically perfect but it worked. That's all that matters. We learn through experimentation. There's never failure just a learning experience.

After Edison had retired he was being interviewed. The interviewer asked how he felt after failing over 100 times to perfect the dry cell battery. Edison said he didn't fail. How so said the interviewer.
Edison replied, I just learned there are over 100 ways how not to make a battery.

That attitude is what successful people possess. Good article and congrats on cleaning up the RF.

73
Phil

 
RE: K6AER  
by AC7CW on November 24, 2016 Mail this to a friend!
Kudos! Amateur radio involves a bit of learning by doing.
 
RE: K6AER  
by K6AER on November 24, 2016 Mail this to a friend!
Amateur radio is a learning hobby but with so many new amateurs coming into the ranks is need to be accurate as well. Antidotal information that may have produced some positive result is not the same as fact based engineering. I wish there was some editorial review when these articles appear. A TV deflection yoke has no ferrite material. The deflection speed needed for TV raster scan what too fast for the magnetitics needed for NTSC format to use any iron based material.

Despite having copper for the core of the choke balun some RF chocking might have taken place. A simple choke balun around a 4 inch PVC pipe would yield more. If the balun is really that effective then why the ground wire on the microphone?
 
RE: K6AER  
by VE3CUI on November 24, 2016 Mail this to a friend!
"...If the balun is really that effective then why the ground wire on the microphone?…"

I don't know --- YOU tell ME…! :o)

To-day's gurus --- such as yourself, quite obviously --- bemoan the fact that even newbies, maybe only just starting out in this wonderful hobby of ours, do not apply established laws of electronic engineering as they "feel" their way about their new environment, at their own risk: and that very well may be…

But, when I started-out in Ham radio 45 years ago, I used a long run of electrical lamp cord for a feedline because it "…kinda looked like 75-ohm transmission twin lead" that was available at the time. Did it work…? No. Did I give up on Ham radio because I failed to follow some "…sound engineering guidelines and principles…?" No.

I simply read whatever I could lay my hands on that was written by Bill Orr, Lew McCoy, or Doug DeMaw at the time, and gamely carried-on.

Tell you what: let ME challenge you self-styled (or otherwise) "experts" for a change --- rather than listing why a certain idea, or application, should NOT work, how about you expounding a little upon the details of why it actually DOES…? Maybe we'll BOTH learn something from such an exercise in "reverse engineering." Because these "fixes" obviously do the job well enough --- at least for me. And as I recall, I did not attempt them on the night of any full moon overhead, either, or on the proverbial "…7th minute of the 7th hour of the 7th day of the 7th month," either…!
 
RE: K6AER  
by KA3AUD on November 24, 2016 Mail this to a friend!
Great point. Ignore the "experts". Too many hams forget ham radio is just a hobby.
 
RE: K6AER  
by K6AER on November 24, 2016 Mail this to a friend!
Common mode RF coming back on the feed line can occur for a verity of reasons. Have you ever looked at the feed impedance of the antenna feed point with an antenna analyzer?

Are the three bands (10, 15 & 20) resonate at their operational frequencies? If not you will have a reflected power situation. Having not enough radials (counter poise) will not allow the antenna to radiate effectively and as a result RF will be sent down the shield of the fed line to act as a RF counter poise to the vertical radiator.

By shorting the microphone to the radio you have electrically shortened the microphone cord to RF and it is no longer resonate at the frequency that you are getting RF burns from. This does not mean the RF choke is working but the hot spot has been moved somewhere else to a hi intensity location. Still you have RF in the vicinity of your station and RF into the microphone circuit is still a problem. Your power supply could be the new hot spot location or some other resonate location.

The simple solution to move your antenna away from the station and make sure the antenna is resonate with the feed impedance. There are no shortcuts in station assembly. A good rule of thumb is the antenna should an minimum one wave length away from the operating location.
 
RE: K6AER  
by VE3CUI on November 24, 2016 Mail this to a friend!
No personal offence meant here, OM, but you've just hit --- squarely on the head of the nail, too, I fear! --- what's so very wrong with our hobby of to-day, with its apparent discouragement of any newcomer "…tinkerers & experimenters" from joining our ranks…

To whit:

"...Have you ever looked at the feed impedance of the antenna feed point with an antenna analyzer?…"

Does EVERY Ham in the world have a shack to-day that miraculously comes equipped somehow with an "antenna analyzer"…? Simple answer: NO. Not here, at any rate...

"...Are the three bands (10, 15 & 20) resonate at their operational frequencies?…"

YES --- as measured the "olde-fashioned" way, with an SWR meter…

"...Having not enough radials (counter poise) will not allow the antenna to radiate effectively and as a result RF will be sent down the shield of the fed line to act as a RF counter poise to the vertical radiator…"

So what's the CORRECT & proper amount of radials to use…? On 2nd thought, don't even go there: ask 3 Hams that question, & you're sure to get 4 different answers...

"...Still you have RF in the vicinity of your station and RF into the microphone circuit is still a problem…"

So tell that to the stations that I contacted a 2nd time who confirmed that my problem with RF on my SSB signal cleared-up after my little fix…

"...Your power supply could be the new hot spot location or some other resonate location…"

At what point, by now, do you think that maybe --- just maybe! --- you totally lost & discouraged any (or all) newciomers…?!

"...The simple solution to move your antenna away from the station…"

A simple answer, alright, but simply not practical in my situation, I'm afraid…!

To summarize: when all else fails, employ the "K.I.S.S." methodology (I don';t think that needs spelling-out here)…or, in lay person's words, "…LESS is MORE."

 
RE: K6AER  
by AA4PB on November 24, 2016 Mail this to a friend!
"A TV deflection yoke has no ferrite material"

I think you are wrong here. I recall TV yokes years ago that had some type of magnetic cores in them (looked like ferrite). We cut out all of the windings and used the core for winding chokes. Probably some of the newer or smaller CRT types didn't use any magnetic cores in them.
 
RE: K6AER  
by K6AER on November 24, 2016 Mail this to a friend!
The ferrite material in a TV yoke is more of a magnetic material and not a 43 or 31 mix used for RF. Different materials have different frequency ranges. Most HF work uses a 43 mix.
 
Choke Close to the Antenna  
by KK5JY on November 24, 2016 Mail this to a friend!
Thanks to the OP for reminding people how to take care of RF-on-the-cable-shield. Most issues I have seen with RFI in the shack were lack of properly choking an antenna. Even if the RF on the shield isn't enough to bite you when you transmit, if the SWR of your antenna changes when you touch the coax shield or some other metal portion of your gear, you need to choke your antenna. Period.

The OP describes an experimental process for determining where to place the choke in the feedline. Always start with the choke as close to the antenna as possible. Read this as "outdoors," if at all possible. You are *not* choking for minimum SWR, you are choking to keep RF off the shield of your cable. With the choke close to the antenna, you may find that you need to experiment on the value of L for your choke, to get the best results, depending on the antenna. But always put the choke as close to the antenna as possible.

I like the ongoing stream of technical articles on eHam. Keep it up, everybody! ;-)
 
Huh? What?  
by AA4MB on November 24, 2016 Mail this to a friend!
K6AER: "A good rule of thumb is for the antenna to be as many meters from the radio as the band of operation."

"I wish there was some editorial review when these articles appear."

Okay ... where to start indeed?

That statement is probably 100% accurate - but how many folks operating on 160 meters can really place their antenna over 400 feet from their transmitter? For that matter, on 80 meters, how many hams can place their antennas over 200 feet away from the transmitter? You may as well have said that a good rule of thumb for successful HF operations is $20K worth of antennas on a couple hundred thousand dollars worth of property. I'm afraid that newcomers wanting to upgrade from Technician class may see this advice and be convinced that HF is not for them. I'm sure that in the annals of radio engineering for AM/FM stations and repeater installations that something like this might be the norm; however, I'd venture to say that easily less than 1% of hams have the sort of real estate and financial resources that would allow that sort of antenna placement. I mean - let's be realistic here. Given my (lack of) issues with the sort of things that the author described in 43 years of unbroken amateur HF operation, it's apparent that good grounding, resonant antennas and a proper counterpoise are much better bangs for the buck - by a wide margin. If that doesn't do the trick, construct/buy RF chokes. Obviously, if you're running 1.5 kw on HF - well, your mileage may vary. Most of us don't. The author was running a 100 watt rig. Following your guidelines, unless he's independently wealthy, he should forget 160, 80/75 and probably 40 meters, too. It's easy to follow the 'one wavelength' guideline if you're running VHF or UHF, also - it becomes problematic if not actually impossible for what I believe would be the vast majority of us in the real world - even on 20 meters.

Ladies and gents we're amateurs; try the simple and practical things first and you'll almost certainly solve the problem years before having the resources and political acumen to put your antennas on a neighbor's lot on the street behind you. This advice is the equivalent of ignoring the magazine right by you and going to the workshop and getting a sledgehammer to kill a fly on the kitchen counter. Will it work? Probably. Is it the most efficient and easy way to deal with the problem? No.

Finally, Lord help us - "editorial review?" Nothing would ever get posted - no matter how 'correct' it was, because 'correct' is only valid when you find a few others to back up your assertions/beliefs. The chances of an editorial board agreeing even most of the time on something for *amateurs* is slim. This isn't life or death medical science, where 'peer reviewed' articles in a medical journal are needed and necessary. It's amateur radio and what the OP was describing is going to get him bitten on the lip by RF until he takes care of it. He's not driving a BMW over a bridge abutment.
 
RE: K6AER  
by AA4MB on November 24, 2016 Mail this to a friend!
"At what point, by now, do you think that maybe --- just maybe! --- you totally lost & discouraged any (or all) newciomers…?!"

^ ^
This!
 
Nip RF Feedback Before It Nips You!  
by YO3CEN on November 24, 2016 Mail this to a friend!
I also use yoke cores for rfi.
Take a look at the next document:

pyland.dreamhosters.com/py2wm/balun/Balun_with_free_ferrite.pdf


 
Nip RF Feedback Before It Nips You!  
by AF7KE on November 25, 2016 Mail this to a friend!
I applaud you for having the courage to post your experiences. You obviously did well in solving/mitigating your issues with RF. Whatever works for you is what is important. There are multiple ways to solve challenges and you found one. Kudos to you. If we had more Elmers out there instead of folks who would rather just bash and beat you up this would be a better hobby. Please don't let them discourage you from making your way in Ham radio. Maybe I missed it as the hour is late and the sandman is calling, but I don't see anybody here trying to help you.
 
RE: Nip RF Feedback Before It Nips You!  
by W1RKW on November 25, 2016 Mail this to a friend!
I would rethink the choke for one simple reason, exceeding the minimum bend radius of the coaxial cable.
 
RE: Nip RF Feedback Before It Nips You!  
by VE3CUI on November 25, 2016 Mail this to a friend!
OK everyone, BEFORE you take keyboard in hand, & list your expert opinion(s) as to why these fixes should NOT work, how about a brave guru, or two, offering his explanation(s) as to why these bandaid solutions DO work…?!

Challenge yourselves, for a change! I'll bet it'll be much harder to explain their SUCCESS, than it might be to predict their FAILURE...
 
RE: Nip RF Feedback Before It Nips You!  
by KB1GMX on November 25, 2016 Mail this to a friend!
Several things...

The old school TV deflection yoke is not just copper coils. Its a ferrite torus usually in 2 or 4 pieces
glued or clamped together then the coils are wounds around it. Is it ideal, maybe, but it was obviously handy. NOTE some are glued on and can fracture the glass if mishandled (implosion danger) so use care.

Usually RF on the mic with resulting feedback is in the end an antenna problem usually due to some imbalance or reflection resulting in RF on the shield and the cases of the radio. It can happen with any radio and any antenna type if small details are missed.

For example a ground plane with ineffective grounding or radials. Dipole with one end on branches or the coax not running away perpendicular for at least a quarter wave. Even a balanced line fed dipole where the balanced line is not far enough away and perpendicular.

As to distance from the antenna that is always more is better and the major agent is power used. More power, more distance. But that also ignores pattern and location. So simple axioms are often inadequate for best results or prevention.

The last item is coax choking. What may work well at 160 may fail totally at 20M. A system view as to what is going on and how to prevent it is advised.

We as amateurs do know one truth, one size rarely fits. A solution in one case is not always applicable to others. IF all else fails we have the Radio Amateurs Handbook and Antenna Manual all of which address the very issue presented.


Allison
 
RE: Nip RF Feedback Before It Nips You!  
by AA4PB on November 25, 2016 Mail this to a friend!
Ref: pyland.dreamhosters.com/py2wm/balun/Balun_with_free_ferrite.pdf

In the above article the author runs tests that indicated the ferrite material in a yoke is between 43 and 61 mix, right in the range that works well for HF. There is your technical reason why the OP had success with his technique.

 
RE: Nip RF Feedback Before It Nips You!  
by K6UJ on November 25, 2016 Mail this to a friend!
Thanks for the great article. I have used TV deflection yoke cores myself for RF chokes. The technical study presented shows:

"The yoke core is a good substitute for a large toroid core, as used in baluns for antennas and antenna
tuners/couplers. With permeability between that of material 43 and 61 it is a perfect choice"

So K6AER's statement that they are just a coil of wire was incorrect. (Consider this a learning experience Mike.) :-)

Bob
K6UJ
 
RE: Nip RF Feedback Before It Nips You!  
by K2JVI on November 25, 2016 Mail this to a friend!
Hello Ed:
Good show!! That to me is one of the best things about Ham Radio-try it!! Often its not what a thing was designed to do-but what it CAN do. A little "scrounge-a-tronics" is a good thing!! I have an example-I'll keep it brief. Made an antenna system using the same balun that DX engineering sold with their 43' vertical-but instead of the 43' vertical, I used longer end fed wires. Even though the balun was supposed to be used with the 43' mast, it works very well from 160-15 meters. I do use several buried radials as a counterpoise. Anyway just one example of thinking out of the box. Keep it up!!!
73's
Bob K2JVI
 
Nip RF Feedback Before It Nips You!  
by KD6VXI on November 25, 2016 Mail this to a friend!
K6AER, you are very wrong on the lack of hf capabilities on the yokes.

I have measured 3 different samples. All 3 new in box, and all 3 provided by a current broadcast engineer. I highly doubt Dennis was pulling any shenanigans.

Regardless, I measured them on a vna. All 3 showed promise in the HF range, including ten meters.

This test was brought about by another ham pool pooing the idea and even more stating they had used them as filament chokes.

A simple lash up with a vector analyzer showed they do work.

That doesn't change the fact that almost everything in this article is voodoo based upon I did a whole bunch of stuff, have no idea what fixed it, but I'm going to armchair engineer some answers. And if ANYONE who knows what they are talking about comes along, I'll berate and belittle them.

I'm glad he got his system 'functional'. Imagine how many MORE contacts he'd make if most of his power was in the ether, not making his wiring warm.

--Shane
KD6VXI
 
RE: Nip RF Feedback Before It Nips You!  
by W1ITT on November 25, 2016 Mail this to a friend!
To try and get back to solutions rather than flame wars... One solution to RF in the shack, especially on the microphone or key, is to attach a quarter wave wire radial at the troublesome frequency directly at the transceiver.
Obviously, in a permanent station, it's best to pay attention to effective and extensive grounding. But for a temporary station, sometimes this would take all weekend to accomplish when you only have the weekend to play. Operating from apartments in college days, and from hotel rooms later on, I have found that a cliplead and roll of hookup wire has saved the day more than once. Just calculate and measure out a quarter wave of wire and lay it out around the room perimeter. there's usually a ground attachment screw on the back of the radio and you are in business. Again, I wouldn't settle for this at home where I like to have a ten inch wide strip of copper along the back of the operating desk and extensive ground preparations but it works in a pinch.
 
RE: Nip RF Feedback Before It Nips You!  
by K6AER on November 25, 2016 Mail this to a friend!
Well I stand corrected. After much research I have found deflection yokes with and with out magnetics.

Now the question is where to you find old TV sets?
 
Nip RF Feedback Before It Nips You!  
by W4HM on November 25, 2016 Mail this to a friend!
I see by the pictures that you posted on your QRZ.com web page that you know nothing about electronics.

On a serious note RFI in the radio shack can at times be a difficult nut to crack. On one hand you do everything that you can according to established techniques and fail. Other times you do uncommon things and they work.

73,
Thomas W4HM
 
Ground radials instead of elevated radials  
by AG4DG on November 25, 2016 Mail this to a friend!
I'm glad that the author found a solution.

Wouldn't ground-mounting a multiband vertical antenna be better than elevating it? For a ground-mounted antenna, the radials lengths do not matter, because the ground just detunes the radial wires anyway. Then it's just a simple matter of minimizing losses in the ground currents by using radial wires to "short" them out.

For a an elevated single band vertical antenna, you just need a few radials of the right length.

But an elevated multiband vertical antenna is a nightmare. You need a few radials of the right length for each band, but you also have to avoid radials of certain lengths. Then there's the need for trees or other supports in just the right places. There are just too many things that can go wrong.
 
W4HEM  
by VE3CUI on November 26, 2016 Mail this to a friend!
Gee Thomas, are you referring to "mois" perhaps, as being the guilty party who "…knows nothing about electronics"…?

Please --- call your shots better than that, so that the "insultee" might better know just who it is that is being "insulted" by the "insulter"…! :o)
 
RE: W4HEM  
by K6UJ on November 26, 2016 Mail this to a friend!
Ed VE3CUI,
He was giving you a complement actually. After looking at your web page it is obvious you have lots of electronics savvy. It was meant as a humorous jab :-) I like the gear you have built and presented on your web site. Brings back memories of my early ham days with radios that glowed in the dark. I remember my
power supply with mercury vapor rectifiers giving off a nice blue
glow. Drifting off here, hihi.

73,
Bob
K6UJ
 
RE: W4HEM  
by W4HM on November 26, 2016 Mail this to a friend!
Yes I was giving VE3CUI a compliment.
 
RE: W4HM  
by VE3CUI on November 26, 2016 Mail this to a friend!
Thomas. jeezus but I feel like an absolute fool right about now…! I am so very sorry --- I just instinctively took what you said to be the complete opposite of what you'd meant…!

But did you notice…? For "insurance purposes" I planted a smiley face at the end of my tome, "…just in case" I somehow read what you posted incorrectly...I guess I've been conditioned to expect the worst from social media through past experience. My bad --- and I apologize again.

Yes, I've been blessed here with an ample tube supply, a hefty junque box, & what I think has been an almost insatiable curiosity over the years to try the unconventional. How many of us can use an HB receiver on a daily basis in to-day's bands that employs tubes that are (well, they WERE, anyway, when I built it in 2003!) older than your own mother…?!

It's challenging, & fun, both. Ditto my "solutions" to the RF feedback/loops at the cottage set-up described in my article. Were the fixes "state of the art"…? Hardly. Were they firmly set in accepted & sound electronics engineering practices…? I don't know --- maybe, by dint of luck & a bit of "…by gosh & by golly," they were.

But as I said, who really cares, anyway…? Just as who really cares that air-is-mixed-with-gasoline-at-a-specific-ratio-then-injected-into-an- engine's-cylinder-chamber-whilst-said-cylinder-is-in-its-upward- stroke-whereupon-the-mixture-ignites-forcing-a-downwqrd-motion-of-the- cylinder-head etc. etc., etc. etc. All that REALLY matters is you get into the car, turn the ignition, start it up --- and away you go.

Sometimes we can all be a tad TOO smart for our own good, when --- as I said in an earlier post --- K.I.S.S. is probably always the safest way to go…and that's what I should have had foremost in my mind, too, when I first read your comments…and for that, again, I am sincerely sorry. I hope that you might see your way to overlook my initial false presumptions, & accept my apology...

 
RE: W4HEM  
by WA1RNE on November 26, 2016 Mail this to a friend!


I would tart with installing the current balun (common mode choke) at the antenna feed point.

Common mode currents are flowing on the outside of the coax shield and will vary depending on frequency, the length of the line, grounding at the station, etc.

Although the TV yoke may be "working", that may not be enough to do the job. A home brew air core choke, a proven design with the correct mix ferrite material or a commercial balun is really what you need.


...WA1RNE
 
RE: W4HEM  
by K6CRC on November 26, 2016 Mail this to a friend!
Just a hobby, of course. Cheap and dirty is fine, many to most hams I talk to are running shoestring budgets. Lots seem to use 30 year old transceivers and speaker wires/fences/rain gutter/eBaySpecials for antennas.
No problem there... But, there are hams who can help you get a real fix and possibly find things wired up incorrectly which can KILL you.
With old equipment, someone probably needs to check your AC wiring, power cords, fuses, and such.
No one says you have to 'touch a soldering iron' or own an Antenna Analyzer. Just nicely ask a fellow ham for assistance.
 
Nip RF Feedback Before It Nips You!  
by N2WJW on November 27, 2016 Mail this to a friend!
Many issues that can cause RF back in the shack, some of the culprits... bad coax, bad or no ground and an antenna that is not resonant would cause feedback, an antenna tuner will not cure this.
Once these issues are addressed and if you're still getting this feedback, drop your power.
 
RE: Nip RF Feedback Before It Nips You!  
by KD7YVV on November 27, 2016 Mail this to a friend!
You usually can find old TV sets and CRT monitors at your local thrift store like Value Village (a NW chain) or GoodWill.
 
RE: Nip RF Feedback Before It Nips You!  
by KB3WGE on December 3, 2016 Mail this to a friend!
Good coax, good connections (soldered of course)& good grounds... are the key..73's ALL und HAPPY HOLIDAYS KB3WGE a.k.a. Jimi*Starr !!!!!!
 
Nip RF Feedback Before It Nips You!  
by KF8HW on December 12, 2016 Mail this to a friend!
Just a thought: the jumper wire from the mic to the radio to cure the zap may be from a frayed/broken ground wire in the microphone cord. Might be prudent to replace the cord, as I have seen this problem before and a new cord corrected the issue...
 
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