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Legal FM Transmitter Frequency

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Orville wrote:

Now that I know what I'm looking for, I found one closer to home from a company over in Miami Florida, cost $9.95 and $8.13 for S&H to my zip, total cost: $18.08

I found this 10Db Attenuator here for anyone else interested in getting one for their MBB E-4000 FM Transmitter: http://www.mpja.com/prodinfo.asp?number=16547+TE

Best deal I've found on an attenutor so far.


Clay, that's a 50 Ohm attenuator. I believe most FM antenna outputs are 75 Ohm impedance. You should be sure to match the impedance of the transmitter whenever you purchase anything that attaches to it (attenuator, coax, antenna, etc.)

However I looked at the manual for the Mobile Black Box Eclipse 4000 FM and I don't see any specification for antenna impedance.

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Hi all,

First Reg,

Communication via voice radio commonly uses 50 ohms. But, I will say that I got into a debate about this about a year ago and got my eyes opened to the fact that some of these little less than a watt transmitters dont seem to care if they are 50 ohm or 75 ohm coax and antennas. And this drove me nuts. Mind you I am an Advance class ham radio op and I was a radio repairman in the Air Force. Oh just for info, 75 ohm coax is common with video, both broadcast and say from a video tape or DVD.

Orville, is correct about the antenna should be fully extended. And depending on how good the circuit was designed for the final amplifer, will determine weather or not the amplifier will be destroyed. How many of you remember the good old C.B. radios? When you installed the radio and antenna. There was a test box you should have connected and ran an S.W.R. test and either lengthen the antenna or shorten it to tune the antenna to the wave length of the signal that the C.B. put out. One full wave length for C.B. equaled 11 meters. This is how many times 27 Mhz would go into 300 Mhz. So if you are operating a FM transmitter on 100 Mhz. Your full wave length is 3 meters. But that is rather long so we use either half wave length or 1/4 wave length. I am sure that the telescoping antenna is not .75 meters in length.

Now to answer Orvilles question. First with a 10db atenuator you will reduce the 500 mW signal down to 50mW to the antenna. Now I am like you with the MBB 4000 and do not have switched or tuned power out like some of the other radios. So, I really do not know for sure what this 10db would do for you. Also things like terrain, WX conditions, trees or other objects that will block signal. All of the above effect the distance your signal will travel, along with the actual placement of your radio and its antenna. I think some have radios that have only 10mW output and they are happy with their range. So, I am going to suggest either a 10db or if you can find a 16db. The 16 db if I am doing my math correctly will drop your signal as such. First 10 db will go from 500 to 50mW. Then the next 3 db will drop to 25 and the last 3 db should take you down to about 12.5 mW.

Your money, I will leave it to you to decide just how much power you want to loose in the attenuator.
Oh, and I looked at that attenuator. Good find. Texas was a good name years ago when I was more active with radios.

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Max-Paul, since the company requires a minimum order of $15 (not including shipping charges), I was going to just buy two of these 10Db "Texas" units and use one first to see what results I get after the installation, then just for my own interest add the second unit in-line and see what happens with the range. I really don't need to broadcast but to the edge of my property line and to the street in front of the house, which is way less than 200'. I think to the other side of the street from my front garage wall, where the transmitter will be placed is around 130-150' to where a curb would be. Don't recall exact measurement, measured it quite some time ago just to see the distance I'd need to transmit out from.



All I know is the antenna on the MBB E-4000 is 33" and has a fairly decent length of coax going to it.



BTW: I was in those CB heydays and it was always a real pain matching the antenna and SWR ratios. Especially if you upgraded to a new CB, you had to go through it all over again because it seemed no matter what, no two CB's were ever the same, even if from the same manufacturer and the same exact model! Oh those were the days, such fun spending hours trying to match those pesky SWR's so you didn't burn up your CB rig!



BTW2: just used an online converter to convert the 33" MBB E-4000 telescoping antenna to meters, according to the conversion calculator: 33 " = 0.8382 m

So it appears the antenna that MBB supplies with the E-4000 is longer than the .75m that you thought would be less. If I read my numbers right and rounding up anything over 5, then the 33" antenna actually comes closer to .84m! .09m longer than thought!:shock: Now I have no idea if this makes any difference or not in the output range.

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Ah, well .75 mtrs would be by the text book. In the real world several things can effect the end results. Like look at the counterpose (see ground plane) and your active element length changes.

Hey one you understand by looking at channel 1 and channel 30 or was it 40? And then depending on which is lower is the direction you would want to move the length of the antenna.
So, you have some coax between your 4000 and the telescoping antenna?

Anyway if anything I have said before in earlier post helps you or anyone else. Then great that is the whole intent of my post, to be of help to others.

Max

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Max-Paul, it's the coax that was hard wired to the magnetic mount antenna. I believe the thin coax (not sure of its rating/id type) is even smaller than the CAT5 cable coming from the MP3 Showtime director to the LOR CTB16PC units. I'd wager the antenna leadout coax at about 1/4 size smaller than the CAT5.



BTW: my attenuators came in this morning (that was fast just ordered them 4/27 at 11:49pm and they were here 4/29 at 9am!

Now at first I wasn't sure if it would work as I was not sure if they were "polarized" in the sense they could only be mounted "in-line" in one direction only, but it appears it doesn't matter which way they are installed to work. I installed the one (haven't had a chance to try it out just yet) it would only fit one way due to the tranmistter connector anyhow, so when I get a chance in a bit, I'm going out for a test ride around the neighborhood and see if this 10Db 50-ohm attenuator has dropped the range any. I'm hoping the one does the trick, mainly because I don't have the room to add a second one in-line due to the box size and how I had to mount the transmitter inside with the MP3 Showtime Director unit.



Will let everyone know how the attenuator and transmitter range works out as soon as I know the results, will definitely post my findings here.

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HOORAY!!! SUCCESS!!! The link I posted to the "Texas" 10Db 50-ohm attenuator in an earlier posting, IT DOES THE JOB! I just came back from a test drive to see where, or if I could still pick up my MBB E-4000 signal as far away in my original tests before I knew about adding an attenutor to decrease the signal.



Now my signal only broadcasts no further than 4 houses down the street from me in either direction! This device worked PERFECTLY and I highly recommend it for decreasing the range to a more comfortable level from the Mobile Black Box Eclipse 4000 FM transmitter. It barely makes it to the street behind the house behind ours.(you can hear it, but it breaks up and drops out often - perfect!)



At least now I feel a lot better about using the MBB E-4000 during my holiday light show displays.

This attenuator cost was $9.95 but the drawback is, the company does require a $15.00/minimum order (NOT including shipping charges), so with shipping and buying an extra set me back $30.00. But it was WORTH IT to me!!!

So if there is anyone locally(Orlando, Florida/UCF East Campus area) to me that uses an Mobile Black Box Eclipse 4000 FM Transmitter and would like to purchase the extra one I bought (since I had to make a $15/minimum order) and pick it up, $10.00 and it's yours!

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Hi Orville,

Glad to hear that the 10db (note little "d") unit worked for you. So, if I remember correctly you say that the MBB 4000 is a 500mW (note the little "m") transmitter and the 10db attenuator knocks that down to 50mw to ever connect to it's output connector.

Again thanks for the feedback. Heaven knows I might end up putting one on my transmitter. Being down in Fla. I dont know the lay of your land and how many things like trees around you. Here we have a lot of cedars and I am sure that helps with knocking down the signal. Plus my transmitter is down low near the floor.

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Max-Paul wrote:

10db (note little "d")

It's also supposed to be a capital 'B' (e.g. 10dB), because the unit is named after a person (Alexander Graham Bell).

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Orville wrote:

HOORAY!!! SUCCESS!!! The link I posted to the "Texas" 10Db 50-ohm attenuator in an earlier posting, IT DOES THE JOB! I just came back from a test drive to see where, or if I could still pick up my MBB E-4000 signal as far away in my original tests before I knew about adding an attenutor to decrease the signal.



Now my signal only broadcasts no further than 4 houses down the street from me in either direction! This device worked PERFECTLY and I highly recommend it for decreasing the range to a more comfortable level from the Mobile Black Box Eclipse 4000 FM transmitter. It barely makes it to the street behind the house behind ours.(you can hear it, but it breaks up and drops out often - perfect!)



At least now I feel a lot better about using the MBB E-4000 during my holiday light show displays.

This attenuator cost was $9.95 but the drawback is, the company does require a $15.00/minimum order (NOT including shipping charges), so with shipping and buying an extra set me back $30.00. But it was WORTH IT to me!!!

So if there is anyone locally(Orlando, Florida/UCF East Campus area) to me that uses an Mobile Black Box Eclipse 4000 FM Transmitter and would like to purchase the extra one I bought (since I had to make a $15/minimum order) and pick it up, $10.00 and it's yours!

Would you ship it?I would gladly send you a payment through paypal or even cash through snail mail.Thanks Dan

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Steven wrote:

Max-Paul wrote:
10db (note little "d")

It's also supposed to be a capital 'B' (e.g. 10dB), because the unit is named after a person (Alexander Graham Bell).

Interesting Steven,

Looks like you are one of very few who use the "B". Actually "db" stands for decibell. And I am at this moment not sure of the Dr. Graham Bell, but it might be. But for as long as I can remember (about 30 yrs) it has always been denoted as "db". Do you have a reference that I can read that supports your statement?

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When I take the time to pay attention to what I'm doing I spell it dB. I do find it interesting that it's not a capital D though (since it was really named after his daughter Deci Bell) :D

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I am believing that the "suffix" bel is, in fact taken from Alexander Graham Bell. And the term decibel means "1/10th of 1 bel".

Oh, and please note there is only one "L" at the end of decibel.

I am just sure Dr. Bell is rolling in his grave . . . :D

Cray

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And don't forget Deci Bell's dog Milli. Without good old dBm this discussion really has no reference :D

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Max-Paul wrote:

Do you have a reference that I can read that supports your statement?

The Encyclopædia Britannica spells it with a capital 'B'.

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Quite frankly I donna care howa itza spelled!!! Aza longa az it woiks! :D

But seriously, as long as it works, that's all that matters to me. Being an electronics tech for years I should know how to do the mW, dB and all the other bazzillions of crazy abbreviations that I've seen, but guess the old timers senility is catching up to me. LOL

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Max-Paul wrote:

Hi Orville,

Glad to hear that the 10db (note little "d") unit worked for you. So, if I remember correctly you say that the MBB 4000 is a 500mW (note the little "m") transmitter and the 10db attenuator knocks that down to 50mw to ever connect to it's output connector.

Again thanks for the feedback. Heaven knows I might end up putting one on my transmitter. Being down in Fla. I dont know the lay of your land and how many things like trees around you. Here we have a lot of cedars and I am sure that helps with knocking down the signal. Plus my transmitter is down low near the floor.


Yep, Max-Paul, the info I got from the paperwork and their website both state the Mobile Black Box Eclipse 4000 is 500mW. And the Attenuator matched up perfectly between the Antenna BNC and the Transmitter BNC, just screwed it on to the transmitter, screwed on the antenna BNC connector and took the test drive. Definitely very happy with the results of the addition! Thank you very much for clearing up and getting me pointed in the right direction to do what needed to be done here! I'd rather spend $30 instead of $10,000, now if I hadn't added this little gem to my transmitter and there's a good chance the FCC may have come knocking on my door! Now I don't feel so apt to see them!:D

My MBBE-4000 is also on the floor, as is the antenna stuck to an old metal lamp base fixture to hold it upright and WITHOUT the attenuator installed, range 5+ miles, in-line 10dB attenuator, that range is long gone. I only have one large oak tree out front blocking any of my signal, a tangerine tree on the East side of the house, no trees in the side (West) yard, grapefruit, 2 orange and a few Crepe Myrtles out back along with a large hedge. Only other blockers would be some flowers and rose bushes scattered all about. And we're basically FLAT LANDERS here, although heading Westward you'll start running into some rolling hills, but pretty much flat where I am.

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Orville

I would gladly buy that extra one you have.If you would ship it to me i would pay through paypal or send you a check or cash through snail mail.Let me know.

Dan

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Thanks Steven,

Interesting read. Although through out the industry I see "db" far more often then the "dB" that you and the link state is proper. And frankly I have seen the "dBm" and the "dbm", although the first more often. As you noted, it is named after someone. But also note it is not that persons actual proper name. So, lets not confuse bel with Bell, ok.

So, what to say Steven. You have shown me an online reference and I can show you many more that use the lower case db. So, I'll call it a draw unless someone uses the upper case for the "d" or "m" then I will call foul.

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rwertz wrote:

And don't forget Deci Bell's dog Milli. Without good old dBm this discussion really has no reference :D


But we really dont need a reference in this discussion. Its all relative anyway! Dear Watson. :D

BTW if you do a google on dbm and go to wikipedia then down to the table. It is interesting to see what different dbm = what power in Watts. Then on the right side of the table there is some info. It says that 100mW = unlicenced transmitters max power.

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Max-Paul wrote:

Thanks Steven,

Interesting read. Although through out the industry I see "db" far more often then the "dB" that you and the link state is proper. And frankly I have seen the "dBm" and the "dbm", although the first more often. As you noted, it is named after someone. But also note it is not that persons actual proper name. So, lets not confuse bel with Bell, ok.

So, what to say Steven. You have shown me an online reference and I can show you many more that use the lower case db. So, I'll call it a draw unless someone uses the upper case for the "d" or "m" then I will call foul.


Just my thought on these "abbreviations", why the heck is the abbreviation for the word "decibel", dB? When if by rights, and the English language, the first letter of a word is the one that SHOULD be capitalized, i.e. Db. When we abbreviate most other words, Street = St, Avenue = Av or Ave, Circle = Cir, so then why do some words get their "MIDDLE" letters capitalized instead of just being all in lowercase or having the first letter capitalized as it should be?

I'd be very curious to know if there is any "real explaination" out there for why this is.

I guess that's why I kept abbreviated Decibel as Db instead of dB, which doesn't make sense to me, db I could accept easy enough, just seems odd to capitalize a letter from the Middle or end of a word, doesn't it?

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Bel is the actual unit of measurement for sound. The deci part is the prefix for one-tenth. So decibel is one-tenth of a Bel. So you do not capitalize the prefix an hence, decibel abbreviated is dB.

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Mark J. M. wrote:

Bel is the actual unit of measurement for sound. The deci part is the prefix for one-tenth. So decibel is one-tenth of a Bel. So you do not capitalize the prefix an hence, decibel abbreviated is dB.

Thanks Mark! Now that DOES make sense. I learned something new that I didn't know. I always thought sound measurement was the full word, decibel, never knew the "Bel" part was the actual measurement of sound.

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Mark J. M. wrote:

So you do not capitalize the prefix

The case of the prefix can be very important. For instance, 10 mW is 90 dB less than 10 MW.

A lower-case 'd' means deci- (1/10), but an upper-case 'D' means deka- (10).

And, according to SearchStorage.com, when a lower-case 'k' is used for 'kilo-', as in kHz, it means 1000, but when an upper case 'K' is used, as in KB, it means 1024.

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A lower-case 'd' means deci- (1/10), but an upper-case 'D' means deka- (10).

And, according to SearchStorage.com, when a lower-case 'k' is used for 'kilo-', as in kHz, it means 1000, but when an upper case 'K' is used, as in KB, it means 1024.




Wow it has been a while since I went through scientific notation. Thanks for the memory. LOL! :D

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Steven wrote:

Mark J. M. wrote:
So you do not capitalize the prefix

The case of the prefix can be very important. For instance, 10 mW is 90 dB less than 10 MW.

A lower-case 'd' means deci- (1/10), but an upper-case 'D' means deka- (10).

And, according to SearchStorage.com, when a lower-case 'k' is used for 'kilo-', as in kHz, it means 1000, but when an upper case 'K' is used, as in KB, it means 1024.

Good grief Steven,

Now it is not the first letter but the 2nd letter that makes a difference. For your examples given of hz and B are two different things because of the 2nd letter. Kilo means 1000 and Bytes are not based on 10. But on 8 so how do you come up with the stuff you do? Please know your Washington apples from your navel oranges.

I mean geez, you see a difference of 1000 and 1023 and then you see khz and KB what has really changed? The answer is "hz" and "b". Hanging your hat on "k" versis "K" is not the real thing that has changed

Ok, we know that "M" is Mega and "m" is milli. We also know that "D" is deca and "d" is deci. Yet I do not know of any difference between "K" and "k". Does anyone else know if there is a difference between a cap K and a lower case k?

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