## Search

56 posts / 0 new

As we soon learn here at Part 15 School a loading coil can bring a 3-meter vertical antenna to resonance.

What we know is that a particular number of turns-of-wire around a round, square or triangular coil form wired in series between the transmitter and antenna achieves resonance, thereby extending the signal range.

Certain variables determine the actual length of coil wire, such as thickness of wire, space between winds across the surface of the coil, and diameter of the coil.

Let's imagine that a single coil reaches resonance with 50-feet of wire.

But we decide to have three coils connected in parrallel. Doing so would require each coil to be wound with 150-feet of wire. Am I right?

Big question: why would we do that?

Answer:  Because we wonder if it would perform better than using one coil alone.

What do we know now:  We don't know if it would matter. But thinking about it makes one curious.

Such is the mental activity of a part 15er during a Labor Day weekend.

Your proposal is interesting and here's some more about coils in parallel.  The inductance (and reactance if the frequency doesn't change) of inductors connected in parallel is similar to the resistance of parallel resistors in that the equivalent inductance is L = 1/(1/L1 + 1/L2 + 1/L3 + ....) so in your example of three coils in parallel, the inductance of each coil would have to be greater than the equivalent inductance.  There is another factor, the mutual inductance, which changes the equivalent inductance but I am ignoring this for now.

The amount of wire will not be a linear relationship so your example of 50 feet vs. 150 feet is likely not correct.  The inductance is proportional to the square of the number of turns and the total length of wire is proportional to the number of turns so the inductance is somewhat proportional to the length of wire (simplifying by ignoring coil dimensions).

Let's say we want to replace a 10 Hy inductor which has ten turns and ten feet of wire with three separate coils.  Each would need an inductance of 30 Hy so when in parallel the equivalent is 10 Hy.  All things being equal, a 30 Hy inductor will need sqrt(30/10) or 1.73 times 10 turns which is 17.3 turns and in our example would need 17.3 feet of wire. for each coil, which is 52 feet total which is 5 times the length needed for the single original coil.

Ain't math fun!

Neil

The "mutual inductance" makes sense now that you've mentioned it, I hadn't recognized the fact that the proximity of the coils to each other would affect the sum of them.

The matter of dealing in lengths of wire not mathematically evenly derived from a single instance is not intuitive and bends the brain in three directions.

By saying that the idea is "interesting" do you mean that it might contribute something worthwhile to performance?

It could give the antenna structure a nice 3-D appearance.

Carl Blare

Carl asked "By saying that the idea is "interesting" do you mean that it might contribute something worthwhile to performance?"

This phrasing was because you had an idea about a configuration of coils which is not the norm for this application and I found it interesting and worth a look because there might be an advantage to this since it is a different way to load an antenna.  I don't think I proved anything re advantage or not but it was interesting enough to pursue based on the wire length question.

People who work with technology tend to use tried and true approaches when designing circuits and systems and can easily miss another possibly better approach.  I have learned to listen to ideas beyond convention because, in my experience, every now and then a better solution is found in this mann\er.  That's why it is "interesting".

Neil

Then I got to wondering what would happen if one of the several coils was fed in reverse, the RF entering at the top of the coil and connected to the antenna at the bottom of the coil, thus throwing it out-of-phase with the other two coils, causing..... what?

Because of the "mutual inductance" the coil relations with one another would be not unlike that of a transformer.

Could it be used to shape patterns? That is, to govern the directional characteristics of the antenna?

The imagination knows no bounds.

Carl Blare

At the ALPB meeting the discussion about loading coils for AM and antenna configurations was brought up after I said that I was getting my Talking House transmitter back from repair. Plus I have a home brew ATU for it that I'll be using with the original wire instead of using the internal tuning circuit as it was discovered that more of the 100mW input is actually getting to the antenna with the home brew ATU. This is because it uses better coils for it.

I with my curiosity blurted out “what happens if someone made a AM dipole with two loading coils one for the hot end and instead of using a ground for your transmitter simply use a loading coil. Both ends of the antenna would be 5 Ft. or you could use 2 4 ft sections to make an 8 ft antenna which would actually be better for me as my Landlord wants to have things sort of short and neat and will allow me to have an antenna so song as I don't drill holes. There is already the flat adapters made for Satellite T and guess what they have the F connectors on them. So if need be I could get the antenna outside higher and my home brew ATU is water proof.

My question was if it would make the range improve ever further with my AM dipole at 8 Ft. Or what about an AM J pole antenna? What would that do to the Talking House transmitter with a home brew ATU?

I want to use AM as a backup for when we have those temperature inversions and you know me I'm off the air on FM when this happens. But at least AM I'm still on air and maybe can gain range and listeners as I'm telling people about the Tecsun Raio's for \$45 that may revive my station on AM and also has the super sensitive FM reception it takes to pull in weak FM stations like mine.

Progressive Rock (Album Rock, Deep Tracks), Classic Rock

http://thelegacy.shorturl.com

http://the-initiative.boards.net/

TheLegacy, I think that a coil between the transmitter ground and the earth ground would act like a resistor and reduce the effectiveness of the ground side of the antenna.

To get the most bang for the buck the transmitter needs to be as direct to ground as possible which is measured by the lower impedance the better... in other words 1-ohm would be better than 5-ohms....

In fact I don't think there's any way that coils in serial configuration could ever provide an advantage with the short antenna, which is why my suggestion calls for coils in parallel, which would lower the impedance of the coil portion of the antenna.

Keep experimenting no matter what they say. That's what I do.

Carl Blare

"... In fact I don't think there's any way that coils in serial configuration could ever provide an advantage with the short antenna, which is why my suggestion calls for coils in parallel, which would lower the impedance of the coil portion of the antenna. ..."

The purpose of the loading coil(s) is to offset the capacitive reactance of the electrically short radiating conductors legally permitted by FCC §15.219(b), so as to achieve resonance of that antenna system -- which for other things equal maximizes its radiation/coverage.

Various numbers/configurations/locations of loading coils contribute different and very significant r-f losses to such systems even if each of those combinations produces a resonant antenna system.

" ... Keep experimenting no matter what they say. That's what I do."

Rich submitted:  "Various numbers/configurations/locations of loading coils contribute different and very significant r-f losses to such systems even if each of those combinations produces a resonant antenna system."

From where I sit that sounds like there's no gain, but worse than that, there's a predictable loss by employing multi-coils in parallel on a short-stub AM radio antenna.

This website leads nowhere but failure.

Carl Blare

"From where I sit that sounds like there's no gain, but worse than that, there's a predictable loss by employing multi-coils in parallel on a short-stub AM radio antenna.  This website leads nowhere but failure."

_________

Possibly not.

Your real-world (and scientifically-based) experiments may prove otherwise, should you choose to conduct them.

Rich having stated:  "Your real-world (and scientifically-based) experiments may prove otherwise, should you choose to conduct them."

Having previously said that combined coils would cause loss it seems ingenuine that Mr. Rich actually believes that experiments, whether conducted in the real-world or anywhere else, would or could produce stunningly surprising results.

On the visceral level I feel we are being trifled with.

Carl Blare

Even Tim and Moby could gain a little ranch with this as he has his ground wire dangling in the air. Instead he could put a loading coil on that ground. It should make it resonate if you do it right which would then act like a dipole.

Progressive Rock (Album Rock, Deep Tracks), Classic Rock

http://thelegacy.shorturl.com

http://the-initiative.boards.net/

TheLegacy, your complex antenna description is not clear to my head and what I need is a picture drawing of how it would be designed.

The difficulty of describing three-dimensional antenna builds with words alone keeps all of us from being understood when we try to describe antenna systems.

I do not understand what you have described.

Carl Blare

CLIP from Reply 12:  ... You could have it horizontal or vertical picture it like a T sort of like those wires that come with your FM stereo receiver. Now both ends of the T would have to separate loading coils one for the right side of the dipole one for the left side of the dipole. One side is hot one side is the ground side of the coax. ...

Just to note that _neither_ conductor of a coaxial cable (OR a balanced transmission line) is either "hot" or "ground."

Both conductors of both such transmission lines convey/pass equal r-f currents that are 180 degrees out of phase with each other.

Okay let me try and describe this a little better. Picture a peace of coax 1 end will have a F connector or PL 259 connector. The other end will have the outer Shield peeled back so that you can see the inner conductor. Now the inner conductor will be connected 2 a coil then the coil goes to a 4-foot rod. The left side of the coax will have its Shield connected to another coil then A-Rod of 4 foot connected to that coil. So you'll have 1 rod facing right the other Rod facing left sort of like a t-shape.   if you turn the dipole if you turn the dipole vertically you have 2 rods one going up with a coil at the bottom one going down in the coil would be at the top with the red pointing down. I hope this describes it plainly enough

Progressive Rock (Album Rock, Deep Tracks), Classic Rock

http://thelegacy.shorturl.com

http://the-initiative.boards.net/

Interesting topic.

Specially because I am currently working on my Chris Cuff AM stereo transmitter.

I am determined and bound to get this thing on the air.

My local store has 100 foot spools of 16 gauge wire.

Were talking 16 gauge coated wire here.

So let's say I was to attempt to build a good loading coil for the middle of AM broadcast band, what would the coil length be? At what point in the windings would I put a tap?

Proposed AM frequency would be 1250KHz. That is what the current frequency that crystal in this thing transmits on. This transmitter is a SINGLE channel transmitter, it does not tune across the AM broadcast band.

Now to get this thing up past 1605KHz, Chris Cuff mentioned getting the following part from Digi-Key:

Quote:

The part number is ECS-P85-A-ND and remember to multiply the frequency times 4 to get the value of the oscillator you want- for example, 1250Khz would be 1250 x 4= 5 Mhz, so you would want the oscillator programmed for 5 mhz. They do this at no additional charge at Digi-Key.

End Of Quote from Chris Cuff's directions.

Now if I moved the transmitter to a frequency above 1605KHz, where would that bring me with coil construction specifics? Length? Number of turns before a tap?

Please, I'm too old to re-learn algebra, so make this easy on me in feet and inches.

Many thanks for catering to an old man in the glue factory pasture.

Bruce.

To TheLegacy... your detailed description of your double-coil dipole antenna is clear for me and I appreciate it.

You have described a symetrically balanced dipole but your feed line with shield and center-conductor coax is un-balanced which means a mismatch when they join together.

The solution is found in radio handbooks and can be home-made... that would be a "balun" to convert unbalanced-to-balanced for an exact match. Baluns are types of RF transformers, and are built slightly differently based on the frequency and impedances involved.

As to whether the double-coil balanced dipole would perform more efficiently than a plain single-coil vertical antenna, I do not know.

To MrBruce... there are formulas for estimating wire length for loading coils with the variables being: a.) frequency; b.) wire gauge; c.) space between winds; d.) diameter of the coil.

When I built my loading coil for the AMT3000 onto a triangular form I used a spectrum analyzer and kept winding wire until I found the peak and for me I think the number of turns ended up being 176 but I never measured how long that wire is.

Carl Blare

Info on same is included in this earlier thread...

http://www.part15.us/comment/31402#comment-31402

Must be nice to own a spectrum analyzer, some of us don't have that luxury, so we are left with guess work, lots of it!

Let's say a piece of 3 inch PVC pipe is used as the cylinder for the wrapping of 16 gauge wire, now we have two of the numbers needed for the equations we would be working with.

Now, someone who understands all this mumbo-jumbo about X times Y plus z equals ? should know the length required for the total length of the wire, then they should also know the number of turns needed before the next tap in the coil.

Example, for let's say 1650KHz, 200 feet coiled 16 gauge wire, wrapped around 3 inch PVC pipe, requires 4 wraps of wire to starting point, then a tap, repeat last instructions until 200 feet is used up, now attach to your radiating element and your antenna should fully resonate at that frequency.

No matter how anyone explains it in these forums, we are referred to the 160M band antennas and now we have to play with scientific calculators to solve the mystery of the AM broadcast band.

There has to be a proven scientific answer out there, like there is for the FM broadcast band for example, there are on line calculators that tell you the exact length the radiating element has to be for a given frequency. AM broadcast band not so much. With Am we are told to purchase expensive equipment and do field strength readings while playing with coils until we either solve the mystery or go nuts trying to.

Bruce.

I am adding this link because I found it to be of interest.

Besides, watching a youtube video, I seen a guy get 2 and half miles to his car radio and he said he built this antenna. It sounded pretty good. Anyways here's the plans.

http://www.sstran.com/pages/COMMON/sstran_buildant.html

Bruce.

I built the coil using the directions shown, but I used some 22 ga bell wire I had.  The antenna I am using is a MFJ Telescoping antenna.  The combination works well, and my range was definately increased.  I am not seeing 2 miles.  But, it works better than my TH 5 did with a 102 whip in the same location (using TH internal tuner).

I have the supplies to rebuild the coil but am going to compress it since I now know how many turns it took in my situation to tune.  The MFJ telescoping antenna makes the entire setup easy to tune.

Working on getting our small town of <4000 local programming.

A loading coil mounted at right angles to the whip has been found to greatly improve the Q, as contrasted to the usual arrangement where the coil is in-linewith the whip.

I have my triangular loading coil mounted at right-angles to my Wintenna, and plan to spend some time analyzing how it affects the verticle portion of the antenna when placed at other angles.

By the way, for stations with no spectrum analyzer you should consider purchasing a TECSUN radio such as the PL-310 and later models that contain field-strength read-outs that a accurate enough for part 15 work.

Carl Blare

Would you mind linking to even _one_ of your posts prior to Reply 22 here to support your allegation pasted above in this post?

BTW, the original source was K6LFH, not "KGLFH" as you stated.

Then you posted in Reply 22:

"... A loading coil mounted at right angles to the whip has been found to greatly improve the Q, as contrasted to the usual arrangement where the coil is in-line with the whip. ..."

Those conclusions were based on undocumented statements for mobile/portable antenna systems using capacity-hat top loading in the 80 & 40 meter ham bands, which configurations are not very likely to be acceptable to the FCC for unlicensed AM broadcast band systems/operators operating legally under Part 15.219.

Suggest that such concepts be fully researched and understood before believing/posting/implementing them as applicable to Part 15 AM systems.

The poster of the right angle loading coil in Radio Handbook was indeed K6LFH as indicated by Rich,

In my original post the "6" looked like a "G".

There.

That explains it.

Perhaps my eyeglasses need a checkup.

Carl Blare

The poster of the right angle loading coil in Radio Handbook was indeed K6LFH as indicated by Rich. In my original post the "6" looked like a "G".  There.  That explains it.

Interesting that you did not respond to my post other than trying to explain why you confused some ham radio call letters.

Have you no further comment/defense relating to the other, and more important discrepancies that you posted in your Reply 22?

Esteemed member Rich asks: "Interesting that you did not respond to my post other than trying to explain why you confused some ham radio call letters."

By all means tell me why it is so "interesting" and we'll continue from there.

Carl Blare

Hey! I did more than "try". I actually explained.

You have a deficit.

Carl Blare

Because you did not respond to the technical details there.

Rich: "Because you did not respond to the technical details there."

Oh, is that all?

Carl Blare

One thing I noticed about the SSTRAN coil placement in the diagrams on the SSTRAN website was that it was essentially coupled "near" the base of the antenna.

I would consider this part of the feedline (obvious perhaps?).   The specs for the antenna length (based on dimensions of copper pipe cuts), the PVC loading coil length and associated wire needed to couple to transmitter etc. very closely "max" out the length available to Part 15 transmitter antenna/feedline etc.

In my build, I integrated the antenna connection to the top of the PVC coil form (cap) and did the same at the bottom using 3/8 x 24 mounting.  Why?  I wanted it to look integrated, and help with any obscurity about actual lengths of radiator/feedline involved with my installation!  Note, I did not necessarily gain any length reduction, but I am within spec with my telescoping antenna after tune up.

I have considered moving the coil inside my metal tool box which would further eliminate its ability to radiate, but would probably "couple" further with surrounding metal of the tool box.  Why would I do this? It would provide better weather protection and keep prying eyes off of it.

I am not able to predict the impact this will have on the antenna matching or performance. I am sure it will degrade performance somewhat, but a coil does not radiate as a rule...so would it??  I am guessing it would "couple" with the ground aspect of the tool box.

All this to say, would the right angle installation matter if it is not in the field where it has been said that the study was done on 40/80 meter with capacitance hats installed?  I have not read the article mentioned above, it is on my list for tomorrow.

I do recall that some of my old ARRL books from the 50's show matching coils in the trunks of various car installations (some with motors for remote adjustment).  I will have to see if I can dig those out, but it is probably not relevent to this discussion, just something I remember browsing thru in years past.

As a side comment, I do not run a capacitance hat on my Amateur radio HF mobile installations.  The blasted wind drag is bad enough for me with the screwdriver (motorized tuning) antennas I use.  I do however, run the full 102 in whip, and at 100 watts I generally don't have trouble receiving or transmitting to whom I want.

I wrote a book as usual...

Working on getting our small town of <4000 local programming.

By the way, when I mentioned the link to the SStran web site, I mentioned a video back in post #20 that is on youtube that I watched where a guy mentioned the SSTran AM broadcast antenna link plans in his description. His antenna is based on those instructions.

I figured it made better sense to add the link to that video to this topic. He takes a test drive, testing the range of his ground mounted AM antenna.

Have a watch.

AMT3000 range check part 1