| Author |
Message |
    
Wolverine
| | Posted on Tuesday, September 16, 2003 - 5:07 am: | 
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I was trying to figure out how to approach, or use the proper wording to get the right answers.
I'll just take a "Stab" at it, ala O.J. Anyway, why are export radios mass produced with what is called "Low-Level Modulation"? It seems to me that this problem would make single-final radios more desirable to purchase for Dxing, and competition shoot-outs because of the booming loudness of less say a cobra or uniden single-final radio. I know that dual finals can generate more rms in watts, but I thought it was all about swinging audio. All anwsers from techs or others are appreciated. Thanks.
Wolverine. |
Kc0gxz
| | Posted on Tuesday, September 16, 2003 - 4:28 pm: |
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Wolverine
All FCC Approved CBs built for entry into the US that are new and unmodified, have less than 80% modulation. The illegal 10 meter radios that are in this country generally have over 100% modulation.
Once some "correctly done" modifications have been done, it's a whole different story for both single and dual final radios.
Jeff, kc0gxz. |
Bruce
| | Posted on Wednesday, September 17, 2003 - 5:05 am: |
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low level modulation means its done before the rf power amps high level means you modulate the final amp its self. What jeff is talking about is a fcc rule requireing audio limiters to prevent overmodulation..... resulting in low leverl OF modulation. What does this meen to you ??? not much as a end user. |
Wolverine
| | Posted on Wednesday, September 17, 2003 - 9:26 am: |
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Excellent answers, Jeff and Bruce. This begs my next questions. If the proper mods can be done to a 10 meter radio, to bring it up to 100% modulation, would'nt it ( the export radio), still be prone to splatter or create harmonic distortions while operating on 11 meter normal cb channels?? In other words, If I'm using my single-final radio against a dual- final export radio in a Dx skip shooting contest, or competetion, Theoretically, I should be the winner only because all of my rms carrier, and modulation is being transmitted on true 11 meters by a radio made for 11 meters. As opposed to a 10 meter dual final export made for 10 meters trying to compete on 11 meters, hoping to xmit all modulation and carrier on the correct frequency of competition.
Does any of this make sense? Am I correct?? Do 11 meter single final radios have louder audio by design, as opposed to low level export types.
Sorry for being so long winded. I just want to make sure that I'm being understood.
Wolverine.
Wolverine. |
Tech808
| | Posted on Wednesday, September 17, 2003 - 11:38 am: |
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Wolverine,
As long as the radio you are useing, be it a CB or 10 Meter(converted), Single or Dual Final radio running on 11 meter's, is properly tuned and you are dead on frequency, and not over modulated, you should have No splatter or harmonic distoration.
A radio signal going out has no idea what kind of radio you are useing to send it, if you are dead on Frequency.
It can be a CB, a 10 meter radio or Ham Radio that has 6 or 8 bands.
A very easy way to check your signal is by useing a scope.
If you do not have one, most Good radio shop's should have one, and let you see what your signal / modulation is doing and what it look's like.
You want a smooth rolling wave with no spikes.
Without a Scope you really have NO idea what your signal is doing.
You can get, Splatter or Distoration with Over Modulation, Too much power, Not Dead on Frequency, Bad Coax, Poor Antenna, Not grounded well, Power Mic's open to far, and many other thing's.
99% of it is not caused by the radio it's self but what people do to the radio & how they run it and the equipment used with the radio.
Just my thought's.
Lon
Tech808 |
Wolverine
| | Posted on Thursday, September 18, 2003 - 5:48 am: |
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Thanks for the clarification Tech 808. This is such a facinating hobby. Propagation, Meters and frequencies, equipment, as well as other important variables to "Shake and Bake a Perfect Cake". But the fun part is the investigation. It really feels good to learn something new, and continue to improve my knowledge, every single day! |
Wolverine
| | Posted on Sunday, September 21, 2003 - 3:06 pm: |
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OOOPPPS. I forgot to ask this question. I'm feeling like a "Columbo". I know that Galaxy Radios or any of the exports have at least 500 channels. I'm Also told that these type of radios have what is called attenuation filters or filtering etc. What is being filtered, or attenuated, and why is it necessary???. Secondly,
would someone tell me which radios that the "TRUCKERS" prefer most- Cobra, uniden, or export radios??. That's all folks.
Wolverine |
Bruce
| | Posted on Sunday, September 21, 2003 - 8:31 pm: |
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Wolverine
Attenuation filter? Unless they are talking about the CRYSTAL / CREMAIC filters in the receiver or the transmitter output filter then i dont have a clue ...
Receiver filters ( crystal/cermaic )
As A RULE most radios use several " filters " to attenuate out of channel signals the most common way has been around for 30+ years and this applys to many radios sold today......
1st IF FREQUENCY
For all mode a 2 pole filter ( 1ST filter) at 10.695 ( some 7.8 ) mhz. Attenuation is +/- about 6khz at 6db and +/- 30 khz with attenuation at about 30 db average.
NOW WE SPLIT SSB/AM/FM
Now most radios to give you the modes split one leg goes to a SSB crystal filter 4-6pole 2.5khz wide the other leg goes to a mixer gets mixed down to 455 khz ( .455 mhz ) and most have a 2 pole creanic filter at 455khz about 6 khz wide.
remember your gain from rf amp to the diode detector can be 100 db ! well these filters reduce everything outside the channel you want to hear by a good part of that final gain. In addition to the filters you have IF transformers all if which comtribute to this rejection.
Rf filter ( transmitter )
FCC rules require out of band signals be down by a given amount the filter at the very output of the final amp does that as well as match the antenna to the final output for best transfure of power.
I hope that might help on the question of filters and attenuation. |
Wolverine
| | Posted on Tuesday, September 23, 2003 - 5:50 am: |
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Thanks Bruce. And yes I was refering to the RF filter on the transmitter side. Great explanation.
Wolverine. |
Bigbob
| | Posted on Tuesday, September 23, 2003 - 6:47 pm: |
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Just keep coming back,you'll LEARN more on copper forum than anywhere else. |
Jwill32
| | Posted on Monday, November 24, 2003 - 11:16 am: |
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Can you tell me what finals are used in the Superstar Grant or President Grant Export radio. I believe these radios are one and the same. |
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