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Electronics => RF, Microwave, Ham Radio => Topic started by: Merlysys on May 03, 2016, 06:24:16 pm

Title: Need info about this FM transmitter (1 of 2)
Post by: Merlysys on May 03, 2016, 06:24:16 pm

I want an FM transmitter to do some experiments with (using load)
http://www.ebay.ca/itm/222099498416 (http://www.ebay.ca/itm/222099498416)

Specs are given as
  - Output power: 3 DBM - 15 DBM
  - Working frequency: 85 MHZ--115 MHZ

Is this really an FM transmitter? If so what would the max power output be? Is it possible to convert dbm to watts?

Title: Re: Need info about this FM transmitter (1 of 2)
Post by: xrunner on May 03, 2016, 06:34:37 pm

Quote from: Merlysys on May 03, 2016, 06:24:16 pm

Is this really an FM transmitter?

Well, that's what they claim. Buy one and see.  :-//

Quote

If so what would the max power output be? Is it possible to convert dbm to watts?

dBm is power relative to 1.0 mW. 0.0 dBm is 1.0 mW of power, so (+) 3 dBm would be twice that or 2.0 mW. (+) 15.0 dBm is 31.6 mW output power.

Title: Re: Need info about this FM transmitter (1 of 2)
Post by: Ammar on May 19, 2016, 12:40:33 am

It very much could be. I assume those SOT-23 packages are discrete transistors. I don't know why they have bothered when there are many integrated solutions. Looks like a cheapy. Expect the frequency to drift if you do get it.

Title: Re: Need info about this FM transmitter (1 of 2)
Post by: mos6502 on May 19, 2016, 08:01:06 am

It's just your standard 3 transistor FM bug. Dozens of circuits out there. Transistors used:

J6 - probably MMS9014
J8 - MMS9018