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.
Biggest issue is, what to do about a loading coil.
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.
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.
Whenever we talk about loading coils for medium wave antennas I like to share this tid-bit from KGLFH printed on page 19.16 0f the Radio Handbook...
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.
Clip from Reply 22 of this thread (author = C. Blare):
... "Whenever we talk about loading coils for medium wave antennas I like to share this tid-bit from KGLFH printed on page 19.16 0f the Radio Handbook..."
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.
Here is a link to a PDF version of this handbook (see page 533 thereof):
http://www.americanradiohistory.com/Archive-Radio/Handbooks/Radio-Handbook-20-1977.pdf
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.
From Reply 24:
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.
Hey! I did more than "try". I actually explained.
You have a deficit.
About Reply 26...
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?
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...