- October 20, 2005 at 6:27 am #6424PhilBParticipant
Total posts : 14
Important info about "Manteca Magnum" antenna
For those of you who are considering the “Manteca Magnum” antenna currently shown on the part15.us home page, there is some important information your should know before you build it.
There are two important points you need to consider about the Manteca design: there are no taps on the coil and there is no mechanism for adjusting the length of the antenna.
If you build this antenna according to the plans, you are doomed to be disappointed. Here is why.
All part 15 compliant base-loaded antennas (including the Manteca) have a very high Q. For those of you that don’t know Q from P or R, a high Q means that the antenna tunes very sharply to resonant peak. Any small variation in the number of coil turns or the length of the radiating pipe above the coil will detune the antenna significantly and reduce your range. To tune this type antenna to absolute peak at your operating frequency, the coil must have a number of tap points and the antenna pipe must be length-adjustable. This is absolutely true regardless of what transmitter you are using. None of the currently available transmitters have any sort of circuit that will compensate for a mistuned base-loaded part 15 compliant antenna.
For one example of a completely tunable base-loaded antenna, see the following web page: http://www.sstran.com/pages/sstran_buildant.html
This antenna will work well if you follow the instructions to the letter. One common problem is that builders try to substitute the #16 magnet wire with other wire they happen to have on hand. The magnet wire has a very thin insulated coating, so the overall diameter is well known. If you substitute some other gauge wire with plastic insulation, the overall diameter is different. The wire diameter and the total number of turns on the coil are critical. Even if a specific plastic-insulated wire gauge were to be specified, the overall diameter of the wire is still unknown because the thickness of the insulation varies across manufacturers and it varies by the voltage rating of the wire (higher voltage rating implies thicker insulation):.
I hope all that are considering building a base-loaded antenna take heed of the importance of what I have said above.October 20, 2005 at 11:45 pm #12624EbachervilleGuest
Total posts : 45366
My antenna desig is based on this and i wil post here my findings, My calcuations were calculated by the Antenna XLS doc, and i did some quite specific calculation of coil length and coil turns so if theis XLS doc is correct my coild should be correct…
I also considered a adjustable mast and after the light of this info i seriously think i will need to make my mast adjustable but that is very simple, i just need to unscrew it, cut neer the 3/4 of the way up and get a few feeet of 3/4″ copper pipe to incert into it and its adjustable..
SO i promis when my transmitter is modified and i hook it up i will give a fair judgement of this design, and then make my antenna adjustable and see if that helps and report those findings.. if that doesnt get me good range i will redoe the entire thing as reccommended and see if that helps… the plus is my grounding and dirt work are doen so i dont have to redo everything if it doesnt work out..
If my coil is way out of wack, i can still tap it with a dremmel and a soldering iron.. so it may not be a total loss 🙂
I do however think that making the antenna the way i did, by using the PVC as the mount for the radiator mast, coil and the post to secure in the ground, made it much simpler and cost effective to build..
We all making this up as we go.. so I’m calling this a learning experiance if it works or deosn’t.. I mean if i dodnt want to mess withbuilding my antenna and or other parts of my station.. i would have either purchaced a antenna or bought a rangemaster.. For many the hobby id the art of broadcasting and for others its the art of building and tinkering.October 21, 2005 at 3:07 pm #12625mlrGuest
Total posts : 45366
Regarding the Manteca Magnum:
I can adjust the freq of the antenna by shortening/raising the length of the vertical radiator.
By placing taps, you lose the PRECISE match. (Taps are great for beginners to search around for freq, or people who are not running a 24×7 operation, by the way)
By using the white pvc, you screw up the inductance SLIGHTLY.
This is a very precise antenna.
RE: The sstran antenna – this is GRAT for people who are experimenting with different freqs, or dont care about getting that last little bit out of the rig. For me, getting it dead on as close as possible was more important than freq hopping.
[quote:43ba36739d]None of the currently available transmitters have any sort of circuit that will compensate for a mistuned base-loaded part 15 compliant antenna. [/quote:43ba36739d]
Some day, we’ll have to show you the manteca transmitter design. 🙂 .
Also – please folks, keep an open mind – 3 years ago, people were claimng that the tesla antenna could not possibly work… now, most of us are using them. FINITE CERTAINTY is almost always dis-proven..October 22, 2005 at 4:09 am #12626PhilBGuest
Total posts : 45366
First, I am assuming the antenna currently pictured on the part15.us home page is the “Manteca Magnum”. If not, could you please supply a link.
Could you please clarify some of your statements?
[quote:a75d7b276b] I can adjust the freq of the antenna by shortening/raising the length of the vertical radiator. [/quote:a75d7b276b]
The plans behind the picture don’t mention anything about adjusting the length. The length seems to be fixed by the bolt holding the two copper pipe sections together.
[quote:a75d7b276b]By placing taps, you lose the PRECISE match. (Taps are great for beginners to search around for freq, or people who are not running a 24×7 operation, by the way)
This statement is not consistent with the very common practice of using tapped inductors and roller inductors (continuously variable tap) in antenna tuner designs going back many decades.
[quote:a75d7b276b]By using the white pvc, you screw up the inductance SLIGHTLY.[/quote:a75d7b276b]
The only way the material can have an effect on the inductance is through expansion or contraction. Is this what you mean? Black PVC pipe is billed as being stronger and more suitable for outdoor use, but on the downside, the black color results from using carbon black in the formulation. The conductive nature of carbon black will give higher dielectric loss. That doesn’t affect the inductance, but could lead to a less efficient coil.
[quote:a75d7b276b]This is a very precise antenna.[/quote:a75d7b276b]
Since you say it performs so well, I have no doubt that it must be very precise. However, its preciseness is not repeatable. Someone following the plans to the letter will likely not end up with a precise antenna. The biggest risk is the coil wire used. The plans call for “#18 (18AWG) stranded and insulated copper wire”. The OD of plastic insulated wire is not standard. It varies among manufacturers and varies with voltage rating. Without specifying the OD in the plans, it is unlikely that a builder will be able to duplicate the “preciseness” of your coil.
[quote:a75d7b276b]Some day, we’ll have to show you the manteca transmitter design. [/quote:a75d7b276b]
This was in response to my statement that “None of the currently available transmitters have any sort of circuit that will compensate for a mistuned base-loaded part 15 compliant antenna.” Your personal design may have such a tuning circuit, but I don’t believe your transmitter design is one of the currently available transmitters.
There are some other things in the plans that make me wonder what is going on here. Hopefully you can clarify.
The parts list calls for:
[quote:a75d7b276b](2) 7/16″ threaded pipe mounts
(2) 8″ 7/16″ heavy copper pipe threaded at each end [/quote:a75d7b276b]
Threaded pipe mounts (flanges) come in standard sizes: 1/2″, 5/8″, 3/4″, etc. 7/8″ is not a standard size. Likewise for the copper pipe standard sizes. You cannot buy threaded copper pipe off the shelf, so cutting threads onto the pipe would need to be done. Standard NPT pipe threads are quite deep cut. The plans call for “heavy copper pipe”. I’ve never seen the K thickness copper pipe. Maybe it’s thick enough, but certainly the commonly available L and M thicknesses are not. Does “heavy copper pipe” mean the K thickness grade or something else?
You show the 1/2″ copper pipe antenna inserted inside the 7/16″ copper pipe. How is this possible when 7/16″ is smaller than 1/2″!
The antenna pictured on part15.us certainly looks nice and it seems to be about as simple as possible (assuming one can find the oddball threaded copper pipe and flange), but the implication that it can be built and perform “precisely” doesn’t add up.
The SSTRAN antenna is just another variation of the common base-loaded 3-meter antenna concept. It has coil taps and antenna length adjustment capability to allow precise tuning. It uses parts commonly available at all home improvement and plumbing supply stores, except for the magnet wire that can be purchased from several on line sources. It may not be as easy to build, but the complete tuning capability is an absolute requirement. The SSTRAN antenna is not a new design; it’s just another variation on the time honored base loaded short antenna. Hams have been doing this kind of thing for 160-meter mobile operation for a long, long time.October 23, 2005 at 5:42 am #12627techpuppyGuest
Total posts : 45366
A simple lesson I learned a long time ago about antennas. You use what works. All of the formulas in the world will not guarantee you a good antenna. I once built a two meter two-element beam for portable use in transmitter hunting. I was extra careful with the measurements and the construction. However I ended up with an antenna that had almost zero signal when pointed at the source. Although it served my purpose, it was exactly opposite of what I expected. The moral of the story is that the ultimate test would be to compare performance of these antennas (Manteca and SStran) at the same site, using the same mast or tower and the same ground system. [b:3a28b3555f]Anyone willing to take that on as a project?[/b:3a28b3555f]
The Manteca Magnum specifies an operating frequency of 1700 for which it was designed. I like the design and simplicity. The SSTran antenna looks like a good one as well, but there’s no way in the world I’m hanging off a tower trying to determine which tap to use or to adjust the length of the main element. Ideally I’d like to know how to make the best antenna for my frequency on the ground.
This site has the best information and helpful members of any I have seen. Perhaps we could all share our antenna performance/range information? No one need be embarrassed by performance. 😉 I will claim the worst performance for a part 15 antenna/transmitter combo of 37 feet. (But the audio quality was incredible.) Naturally I learned from my mistakes or I would still have a potential audience of 3.
What is working for you?October 23, 2005 at 7:23 am #12628PhilBGuest
Total posts : 45366
Just to clarify my intentions.
I am not trying to pit the merits of the manteca antenna against the SSTRAN antenna. The SSTRAN antenna plans are in the public domain and can be freely copied. http://www.sstran.com/pages/sstran_buildant.html
There is no reason for SSTRAN to promote this antenna other than to ensure success for SSTRAN customers.
I just want customers to be successful with an antenna/transmitter combination that works. I don’t want to see customers frustrated when a different antenna design does not perform to optimum expectations.October 23, 2005 at 4:00 pm #12629mlrGuest
Total posts : 45366
You just can’t please everyone, Phil.
So far, anyone who has built the magnum, with the proper number of windings for the right freq, have had excellent results. So, I base my findings off of the designer (A physics professor from Stanford – cause I sure as hell don’t understand the deep meaning of this stuff), and my own experiences, and the experiences of a few people I helped out.
I have never built the Sstran Antenna. I’ve never seen one in operation. I have built several of the Magnums – and I have seen them in operation. These are intended for use in serious application, where you wont be channel hopping.October 25, 2005 at 3:47 am #12630jbprptcoGuest
Total posts : 45366
The SSTRAN antenna has obviously been designed to work with the SSTRAN transmitter, and I want to say that the two of them together do a very good job, and I highly recommend to anyone coming into part 15 without transmitter/antenna to seriously consider the SSTRAN combination as probably the best quality for the money one can get. That having been said, I’ve had trouble tuning other 100mw transmitters to a 3 meter bottom coil loaded antenna. Can anyone kindly comment on their tuning procedures and the distance they get. As to the Magnum, I’d like to know what transmitters/antenna tuning you fellows are using to get good results. Thanks, JimBOctober 27, 2005 at 12:40 am #12631EbachervilleGuest
Total posts : 45366
I would have to say, I made a antenna based on the magnum.. using the calculator excel sheet in the forum.. It did work and got out a radius of a couple of blocks…
I changed the mast to a adjustable one like the sstran uses, mine was of 1″ and 3/4″ copper pipe.. after tuning i get out about a 1/4 mile raduis from my antenna.
So the tunable antenna does help.. I do feel this adjustablility of the coil and mast can make it perform much better..
Im going to build a new coil as the sstran site recommends and use the same ground mounted system and the same gound radial system.. so for the coment above, that should qualify.
Right now im covering town durring the day and at nigh i get beat on by the big guns out there..
I will build this once my wood burner is installed, the weather is getting cold and the free heat will help pay for the TX hobby 🙂
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