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Post by End80 on Jan 22, 2017 9:38:24 GMT
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Post by Deleted on Jan 22, 2017 14:41:00 GMT
Well This Is Interesting
The article from 1961 makes for fascinating reading, so I thought I'd see what the FCC Rules of today have to say about this particular frequency range and this is where it gets even more interesting...
Listen to this from the 2017 rules...
15.227 Operation within the band 26.96-27.28 MHz
Compared to the 1961 rule that's an increase in available bandwidth from 300 kHz to 320 kHz.
Another change is that in 1961 the allowed power level was based on 100 mW to the final RF, while in 2017 the allowed power is stated as:
17.227 (a) The field strength of any emission within this band shall not exceed 10,000 microvolts/meter at 3 meters.
Another significant change is that, whereas in 1961 the antenna was restricted to 5-feet in length, the 2017 rule does not mention any antenna restriction.
Still another interesting observation about this frequency band is that it falls right across CB channels 1 through 28.
And this... the center frequency of this bandwidth is 27.120 MHz, falling between CB channels 13 and 14.
Further, 27.120 MHz is the 1st harmonic of 13.560 MHz, where another rule (15.225) allows 15,848 micovolts/meter at 30 meters with no antenna restriction.
Our big discovery by scouring all this information is that the transmitter project shown as The Roof Hopper is not only a great Part 15 discovery, but can actually be enhanced to bring it up to today's allowances!
Thank you End80.
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Post by End80 on Jan 22, 2017 16:48:02 GMT
In the orange illustration drawing and title 'Roof Hopper' which introduces the article showing a house and antenna (shown above) represents how the transmitter is actually installed... I couldn't help but associate it, in light of recent other discussions, with the Isotron - which of course is an entirely different creature, but the horizontal install of the antenna made me think of it anyway. The article is five or 6 pages long and gives complete instructions on how to construct it. You can download the entire issue from the link provided in my previous post, should anyone be interested.
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Post by End80 on Jan 22, 2017 16:57:45 GMT
"Still another interesting observation about this frequency band is that it falls right across CB channels 1 through 28.
And this... the center frequency of this bandwidth is 27.120 MHz, falling between CB channels 13 and 14."
So I suppose this transmitter is essentially a roof top walkie talkie
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Post by thelegacy on Jan 22, 2017 21:41:09 GMT
I wonder if this design for a dipole could be modified for AM?
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Post by Deleted on Jan 22, 2017 21:56:56 GMT
Not Good News
TheLegacy asks: "I wonder if this design for a dipole could be modified for AM?"
My guess is that YES it could be used for the AM band but once we apply the limits of 15.219 it probably wouldn't be worth the trouble.
The dipole consists of transmission line and a positive and negative length of antenna. BUT once you whittle the lengths down so that the total of antenna and transmission line equals 3-meters you'd have a very short-stubby antenna.
And there's one more hurdle....
All of the part 15 AM transmitters have an unbalanced RF output, but a proper dipole requires a balanced transmission line, so there would need to be a balun (matching transformer) which might not pass every drip of power... but I am not sure... there are so-called step-up transformers which might actually introduce gain, so I hope we get a comment from another radio engineer on this particular point.
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Post by Druid Hills Radio on Jan 23, 2017 14:39:06 GMT
I once had an Ocean Hopper.
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Post by End80 on Jan 23, 2017 20:45:28 GMT
I once had an Ocean Hopper. So did I, recently, though I kept it just inside the mouth of the river leading to the open ocean. |
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Post by Admin on Jan 25, 2017 1:52:32 GMT
Another interesting fact compared to the 1961 rules is that no license has been required for the common 5 watt 40 channel CB for over 40 years.
The antenna can be most anything such as a 1/4 or 5/8 wave ground plane or multi element 1/2 wave directional antennas as long as its not more than 20 feet higher than the structure its mounted on (special height rules if near an airport.)
And the coax can be as long as you can tolerate.
Of course its still considered illegal to broadcast on that band.
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Post by Deleted on Jan 25, 2017 2:00:34 GMT
Admin Has Said
"Of course its still considered illegal to broadcast on that band."
Of course Admin is referring to the CB band at CB frequencies and CB power levels, which is absolutely true.
However, it IS legal to broadcast within this band under the Part 15 rule mentioned earlier in this thread or in another thread.
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Post by End80 on Jan 25, 2017 2:01:13 GMT
I didn't realize a license was ever required for CB.
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Post by Admin on Jan 25, 2017 2:07:23 GMT
Yes, my first was in 1964 - KNN-7431. I believe it was a 5 or 7 year license.
When that one expired I got - KBPG-0551. By then they decided to waive the license fee.
It was after the second one expired I found that a license was no longer required. Instead the FCC suggested using your initials and zip code preceded by "K" if east of the Mississippi and "W" if west of the river. Or, just use a "handle".
I choose to go by KRF-44221 or Crusty Ole Bob!
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Post by jimhenry2000 on Feb 4, 2017 6:56:15 GMT
True but in 1961 a license was required. I got my first CB license in 1963 in my father's name as I was under 18. We gave it up in the 70s when the band went to hell. I guess we were among the few who meant to comply with the rules, using the band for "necessary personal and business communication. This of course means that if you are in your home and the person you wish to talk to is in his/her home, that if you each had telephones then there would be no justification to use CB. Another interesting fact compared to the 1961 rules is that no license has been required for the common 5 watt 40 channel CB for over 40 years. The antenna can be most anything such as a 1/4 or 5/8 wave ground plane or multi element 1/2 wave directional antennas as long as its not more than 20 feet higher than the structure its mounted on (special height rules if near an airport.) And the coax can be as long as you can tolerate. Of course its still considered illegal to broadcast on that band. |
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