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looking for info on how to build one of these
http://isotronantennas.com/index.php?main_page=product_info&cPath=1_4&products_id=15need to make it 10ft or under and cover mid band.
looking for info on how to build one of these
http://isotronantennas.com/index.php?main_page=product_info&cPath=1_4&products_id=15need to make it 10ft or under and cover mid band.
1550 and 1620 seem best here with 1550 having less noise.
Total posts : 45366The Isotron is very interesting to read about and see in pictures.
I am fairly sure that RFB says he either has one or has used one with great success. Calling RFB….. would you mind repeating what you said?
Got to get one. Or, got to build one.
The Isotron would make a GREAT review subject for the proposed part15.us review service.
Total posts : 45366This subject has been discussed here over the years. Here is one thread…
Total posts : 45366“I am fairly sure that RFB says he either has one or has used one with great success.”
The Isotron antenna is an antenna designed for and meant for operation situations where there is little to no room for a conventional vertical monopole over a grounding system. This antenna does not work on the principles of vertical monopoles.
As noted in the other linked thread about the Isotron, it is a resonant “LC” tank, no different from the LC tank in an oscillator circuit. In this case, the LC tank is much larger and is “excited” by the signal from the transmitter.
It has it’s own return path which completes the RF circuit within the antenna itself. This is why when an Isotron is mounted on a metal mast, the mast will not radiate because the antenna does not rely on that mast to be the return path.
Tuning the Isotron is a bit tricky but really no more different or difficult than tuning a 3 meter vertical while wrestling with the external inductive effects during the tuning. In fact, the Isotron is not as sensitive to these external influences like the monopole is.
It is an excellent alternative for those living in apartments or in areas where antenna masts are not welcome. It falls within the 3 meter maximum length regulation and once again, requires no external grounding system.
There is no reason not to try it.
RFB
Total posts : 45366[quote=kk7cw]The Isotron is, by design, a tuned L-C tank circuit, resonating within itself. The characteristic impedance of the device over ground produces the propagated radio signal.[/quote]
Some recent posters appear to agree with this, which they are free to do.
Here is a clip from my post in that long thead, which may have been missed:
From their appearances, the Isotrons for “ham” radio applications are constructed differently than the one for Part 15 AM. The ham versions appear to be very short, loaded doublets (dipoles), which are balanced antennas not needing a connection to an r-f ground to radiate as efficiently as that design allows. Not so for the Part 15 version.
Total posts : 45366If there are different versions are they both true Isotrons, or is one of them similar to an Isotron?
Total posts : 45366The differences with Isotrons designed for ham band use and the one designed for the mw band is really nothing more than the differences between a monopole used in the mw band versus the 180m band, or 80m etc. Size is the only thing different, but all defined the same..a monopole.
So the Isotron name given to the design does not change because the antenna itself changes size or shape to work a particular band.
And obviously the Isotrons built for ham band use will be different for the one designed to work the mw band. There is no common link here between the two other than they are called Isotron antennas. And the mw band Isotron does not need an rf ground.
RFB
Total posts : 45366And the mw band Isotron does not need an rf ground.
For further thought, note that page 16 of the Isotron document linked below states that it is desirable to use a good earth ground with the Isotron 160C.
Figure 1 in the same document shows an attachment point on the antenna for a ground conductor, and Figure 6 shows a conducting path for that ground conductor to a metal mast specified to support the Isotron.
The document also states that height enhances performance best and not to sacrifice height, and that Isotrons are designed to be installed on a light (metal) mast. This affect on performance would be similar to using an “elevated” installation of a Part 15 AM transmitter with an attached 3-meter whip and a long, radiating conductor attached to its r-f ground terminal.
The 80 meter Isotron manual also shows that ground path and height comment – I didn’t check the rest of the models.
http://www.isotronantennas.com/ (Manuals link there)
Total posts : 45366one of these days i’ll get adventurous and build an e/h.
i will design a RF filter that passes DC (and AC audio) while filtering AC/RF at AM B,cast from ground, audio and power leads.
then hopefully one day i can put a tx over a full ground plane at dirt ground potential and compare RF f/s between the two.
as far as i know it’s only me (FIM), RFB (with his SA) and bill defalice (FIM) who are the only part 15’ers with capabilities to make these comparison measurements. I could be wrong though.
let’s take a check in of those with capabilities to make comparison f/s measurements either with a FIM or SA.
i have capabilities with both fim and SA for AM, SA for FM
Total posts : 45366In its principal configuration, the Isotron is an inductively top-loaded monopole, which is very well known. I have used this configuration myself, and it can work reasonably well. The antenna promoters don’t tell you that it is mostly the wire or transmission line to the Isotron that radiates, and not the Isotron itself.
As for the claim that no ground radials are needed, well, that’s somewhat true. It all depends upon how much efficiency you want. Without radials, the earth itself will serve as a ground plane, although a poor one. You can use a ground rod and no radials, but efficiency will be better with radials.
The Isotron and other antenna designs of similar type have been discussed for years on this website. In one of these discussions, I jokingly promoted my “invention” of the “No-Field Antenna,” which is a play on the term “Crossed-Field Antenna.” Just suspend any object in the air (metallic or not), connecting said object to a wire, metallic rod, or transmission line, and it can be made to radiate. The suspended object can be a garbage can lid (even plastic) an EH, CFA, an Isotron, or just any small hook or terminal to which the suspended wire can be connected.
To make my own inductive top load, I have used a large polyethylene bucket as the form for a coil that is mounted on top of a copper rod over the earth, and resonates with the sum of the capacitance of the coil and the capacitance of the rod (the large size of the coil provides capacitive as well as inductive top loading). The coil has to be tuned for resonance. My top load is arguably an Isotron configuration, but it costs much less than a commercial Isotron.
Total posts : 45366“The antenna promoters don’t tell you that it is mostly the wire or transmission line to the Isotron that radiates, and not the Isotron itself.”
That may be so with the ham versions or even the MW version if fed by a coax. However since this is Part 15.219 we are talking about, there is no coax involved, nor was there one involved in my Isotron setup.
Although the Isotron will perform better with a ground radial system, the bottom line is that it does not necessarily need it in order to perform to begin with. And for apartment dwellers and other situations where dirt is several floors down or there is nothing but brick and cement, the Isotron is a worthy candidate.
If considerations of the Isotron were focused on the application at hand…IE the lack of access to good earth ground, instead of trying to compare the MW Isotron to it’s ham cousins, the confusion and diversion will be less.
RFB
Total posts : 45366This is one of the most interesting threads
I’ve seen.Did I miss somebody saying this? I guess the
Part 15 AM transmitter has to be mounted
on the AM BCB Iostron.I also find the idea of a bucket/coil top hat to
be quite intriguing.Bruce, DRS2
Total posts : 45366“I guess the Part 15 AM transmitter has to be mounted on the AM BCB Iostron.”
It would follow the same practice as with a plain ol monopole, the TX being mounted at the antenna since 219 says total length including feedline and ground lead and antenna itself cannot exceed 3 measly meters.
So I am sort of confused why anyone would even mention coax or be comparing the MW Isotron to the ham band versions, where the hams can use a coax if they want. 15.219 does not have that choice unless your running the TH/iAM with the external ATU and those units cannot operate legally unless your using what came with the thing..the TX and it’s ATU, all of which were certified and carry that certification number.
No one’s monopole is certified either so please let’s not throw in the bent card of “well the TH/iAM has a certified monopole antenna”. Irrelevant.
The Isotron for the MW band meets the requirement for the 3 meter length limit in 219. The FCC does not care what kind of antenna your using, a pole, a wire, a coat hanger, an old aluminum Christmas tree, so long as any or all of that is within the 3 meter length limit. The MW Isotron is within the 3 meter length limit, thus qualifies as being legal to use under 15.219, and thus is why the manufacturer calls it “Part 15.219 MW Isotron”.
It does the job very well especially for those living in upstairs apartments with no means of easy access to dirt ground below them.
That is what the MW Isotron is designed for, as pretty much all of the Isotrons for whatever band, are designed for use in tight confinement where space is limited or outdoor antenna systems are not allowed. Those of you on HOA’s and whatnot can find these Isotrons to be a headache saver and will fit nicely in your attics and no more HOA no-antenna no flowerbed no color no freedom over your own home nonsense.
RFB
Total posts : 45366I just went over to the site and
it also looks like the Part 15 AM Isotron
needs a 50 ohm source. But you guys
have probably already mentioned that.If you did, I might have missed it.
Man, I wish I could buy one just to try it.
Bruce, DRS2
Total posts : 45366Right, Bruce, now that you mention the 50-ohm impedance of the Isotron I remember we had a previous thread on this subject where we realized that some of our favorite transmitters would not match with an Isotron.
The repetition is good, I think, because it sort of drums the information into our heads until we eventually know it.
Maybe there is a way of slightly modifying the Isotron to the impedance of our favorite transmitter.
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