- June 23, 2019 at 9:37 pm #111696ThelegacyParticipant
Total posts : 298
let me see if I understand what you’re saying. What you are suggesting is that somewhere there is no connection to the outer Shield of the coax right? Well if this were true you would have a lot of radiation coming from the output of the transmitter to the range extender but by the time it got to the extender to be tuned you would have lost a lot of power as most of it would be radiating out of the coax.
This really makes no sense if that is what you are saying it would make more sense just to use leaky coax going up to the ATU which then would radiate.
The fact that the coax is well shielded would keep it from radiating until it got to the range extender itself. The shield in this case becomes sort of a block to make sure that the radiation is going out it’s intended place the ATU. I’m quite sure you already know that but just to make sure anyone reading this that doesn’t know now they do know.
As we have also seen Tim in bowlby’s test of his procaster he is getting about 1 1/3 miles before it goes to Fringe area but remember he’s about three stories up so that’s about 30 foot or so give or take from the ground.
I think we really need to see what type of range this thing is actually achieving before we pass any type of judgement and I can’t wait until a real test is done maybe even a video of the range itself. I’m going to stay tuned for this one.June 23, 2019 at 9:38 pm #111698ArtisanRadioParticipant
Total posts : 526
I can answer a few of your questions.
The Rangemaster can (and should be) tuned to provide exactly 100mw input to the final. There are two ways to do this. They provide a module that indicates when you are exactly at 100mw, but I’ve never trusted that (the one I had was difficult to read). However, there are also measurement points in the transmitter that allow you to calculate when you reach 100mw (P = I * V).
From what I’ve read in the FCC and Industry Canada databases, most other certified transmitters are approximately 80 mw input to the final (and of course, much, much less output at the antenna, generally less than 1 mw even with the best installation).
As to the Range Extender certification, from what I understand, the manufacturer managed to convince the FCC that the Range Extender was the final stage in the transmitter system. This allows them to connect the Talking House with the Range Extender via coax without violating the ground lead rule. The concept is actually very similar to what radio8z was talking about in one of his posts, and he was postulating connecting the stages via CAT5 cable.
There have been extensive discussions surrounding the Range Extender in this Forum and others for many years. The manufacturer insists that they have the paperwork (and it may well have been published here, I think) that proves that the system is FCC Part 15 certified. I’m too lazy to look it up, but I’m sure that you could find it if you searched. The certification has been treated as fact for many years by virtually everyone in the field, and the FCC has done nothing to dissuade that opinion (i.e., by issuing NOUOs to users of the technology).
I personally believe that the manufacturer managed to pull a fast one on the FCC. A similar type of product for the Talking Sign (the precursor to the ProCaster) was not able to get certified in either Canada or the U.S. and the company was forced to take it off the market. But as I, and I believe you, have stated plenty of times, the Part 15 rules and the rules of physics are not necessarily the same thing. Part 15 rules are open to interpretation (and the FCC has lots of discretion). Physics (ideally) is not. The two are often mixed up, and that’s where some of the heated discussions surrounding this topic originate.June 24, 2019 at 3:53 am #111703RichParticipant
Total posts : 195
Below is a graphic showing how r-f current can flow on the outer surface of the outer conductor of a coaxial cable.
This occurs even when the termination at the far of that coax exactly equals the characteristic of the coax connected there (often 50 +j 0 ohms).
That current flowing along the outer surface of the coax outer conductor produces e-m radiation into space for the same reason it does when flowing along a conductor leading back to the inner conductor of the coaxial cable.June 24, 2019 at 4:55 am #111705
Well, yes. I think that is what he was trying to tell me and no, it didn’t make sense to me either.
Thanks for your comments.
W9LWAJune 24, 2019 at 5:03 am #111707
Thanks, Artisan. That sounds right to me.
W9LWAJune 24, 2019 at 5:11 am #111709
Thanks for your comment, Rich.
So, does that mean:
1. The TH is actually sending RF up that coax and getting another 25 feet of antenna+lead; and,
2. Another 25 feet of ground through the coax braid?
W9LWAJune 24, 2019 at 5:51 am #111712RichParticipant
Total posts : 195
With a perfect impedance match between the coax and the load at its far end, the current flowing on the OD of the inner conductor is equal to the current flowing on the ID of the outer conductor, but they are 180 degrees out of phase. Therefore their radiated fields cancel.
But when the current on the ID of the outer conductor reaches the far end of the coax it finds two paths to travel along, one being the OD of the coax outer conductor. The current traveling along that path produces radiation.
Radiation will also occur from any conductor connected to the OD of the coax outer conductor at the tx end, including the path from the transmitter chassis along the “ground” conductor of the a-c mains service until that conductor connects to the ground rod at the service entrance.June 24, 2019 at 6:57 am #111714
Indeed, that’s how they’re getting away with it.
W9LWAJune 24, 2019 at 9:49 am #111716AMRadiolegendParticipant
Total posts : 334
How much RF is radiated with the cable on the ground. It’s time to drop this subject and move on to newer paranoia.June 24, 2019 at 10:46 am #111718ArtisanRadioParticipant
Total posts : 526
If, as the manufacturer claims, and the evidence indicates, the entire system is certified, then the amount of additional radiation introduced by the coax cable is insignificant.
In addition to that, the radiation introduced by coax in a properly matched antenna system is minimal, regardless of whether it is possible or not.
I suggest that if anyone really has their knickers in a twist about the potential radiation the coax, along with the Range Extender, introduces in the Talking House system, they purchase said system and actually measure it (as I’m sure the lab in the certification process did).
If further theoretical discussions along this line are desired, they should be taken to another thread.June 24, 2019 at 3:56 pm #111720
Well Legend, I think I’ve figured out everything I wanted to know about the grounding of the range extender, anyway. What I’d really like to know is if you have yours operating yet and if so, how does it sound and what kind of range are you getting?
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