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Could anyone just take a look?

Discussion in 'General Electronics Discussion' started by ntiwari, Aug 14, 2012.

  1. ntiwari

    ntiwari

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    Aug 12, 2012
    Hey guys
    I am very new to the whole PCB thing, and was wondering if anyone minded just taking a look at my new design for a 40 watt fm amplifier. Just to clear things up, the three pin terminal blocks should be where the smp connectors go. All of the other blocks are inductors. Also, does it matter how many windings a coil has, just as long as it is the same inductance rating, or do you have to stick with the schematic?
    Thanks,
    Nick
     

    Attached Files:

    Last edited: Aug 14, 2012
  2. CocaCola

    CocaCola

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    Apr 7, 2012
    Is there another layer or are you going to do point to point wiring for the rest of the connections? As it sits it appears only about half the routing is actually done, leaving a lot of connections just floating...
     
  3. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Looks like the seemingly open conenctions are to a GND plane on the other side of the PCB. This would be a good idea for an HF-amplifier.

    Apart from that the placement of the components looks a bit random to me. Personally I would have tried to mimick the signal path in the layout as it is is shown in the schematic. This means a more oblong PCB, not square. That way input and output are at opposite ends of the PCB. This minimizes the risk of crosstalk from out to in.
     
  4. john monks

    john monks

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    Mar 9, 2012
    Did you do a prototype first?
    I noticed on the schematic Q1 is a MRF171A and Q1 on the pc board is ZVN3306A.
     
  5. ntiwari

    ntiwari

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    Aug 12, 2012
    Ya most of the connections go to ground, there are only about 3 that are completely inline.
     
  6. davenn

    davenn Moderator

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    Sep 5, 2009
    true definately some serious problems ....

    1) --- that ZVN3306A is NOT a replacement for a MRF171A the MRF171A is a hi power RF transistor the ZVN3306A is a 600mW general purpose MOSFET the 2 are not interchangeable

    2) --- You CANNOT use that sort of layout for hi power RF, you will end up with all sorts of oscillation problems

    3) --- The MRF171A when you finally show it in the layout MUST be heatsunk its going to get VERY hot with it capable of 40W output its going to be using probably twice that ~ 80Watts from the PSU

    4) --- You CANNOT use strip terminals for terminating RF input and output. You MUST use proper RF connectors like right angle SMA connectors, mounted ON the board
    ---- it seems there are screw terminals all over the circuit board ?? if thats what they are, they must be taken out

    many of these things would be apparent to you if you looked at the PCB layout in the MRF171A datasheet You may find the datasheet a little hard to find and have to go to Motorola or as they are now known as ON semiconductor or Freescale

    When building RF equip, PCB layout is critical for correct operation of the unit
    You cannot have other general components close in around the power device as they will pick up radiated signal from the transistor and cause all sorts of feedback problems. the only time you will see components close into the device is when very small value chip capacitors are used to stabilise the device

    You are going to nedd to have or have access to a quality RF power meter capable of the power levels you expect to measure
    You are also going to need access to a spectrum analyser to tune your amplifier to make sure you are not splattering all over the spectrum with harmonics and spurii

    cheers
    Dave
     
    Last edited: Aug 15, 2012
  7. davenn

    davenn Moderator

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    Sep 5, 2009
    Im at work at the moment and dont have access to datasheets and general PCB layouts for VHF amplifiers that I have on my home PC. When I get home tonite I will have a look and see what i can find for you to help you on the right path.

    Just keep in mind you will have to do a complete PCB redesign OK

    Dave
     
    Last edited: Aug 15, 2012
  8. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Personally, I'm amazed that anyone here is helping you. This thing is illegal in most countries and definitely in the U.S. Probably in Australia too! 40 Watts can play havoc on receivers for well over a 10 mile radius.
     
  9. davenn

    davenn Moderator

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    Sep 5, 2009
    yes it is here too

    dunno where the OP is located


    D
     
  10. donkey

    donkey

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    Feb 26, 2011
    we have VERY strict rules here in australia about broadcasting, this would most definately be illegal without prior written consent from a few organisations.
    I like the idea of everyone having a say, but it HAS to be monitored for several reasons and in this case it is so you don't use a bandwidth or interfere with a bandwidth that is important
     
  11. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    He might have an amateur radio license?
     
  12. john monks

    john monks

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    Mar 9, 2012
    Ntiwari, what do you intend to do with this?
    Do you have a broadcast license?
     
  13. donkey

    donkey

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    Feb 26, 2011
    ntiwari as with the above questions I add a few more
    do you require a broadcast license?
    are you aware of the implications of activating this device?
    and how are you going to stop it from interfering with other transmissions?
     
  14. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    I have an amateur radio license and I also have a commercial radio telephone license. Neither gives me license to transmit on the commercial FM band. Actually, to be more precise, My commercial license authorizes me to service, repair, tune and operate land and ship stations but it does not give me license to setup my own transmitter. That's a radio 'Station' license, where the channel frequency, transmitter and antenna are licensed. A Ship Station license covers the transmitter, receiver and antenna. The channel frequencies are shared among the maritime services. ;)
     
  15. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Let's get real here. The only category that this could possibly fall under is "Pirate Radio".
     
  16. john monks

    john monks

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    Mar 9, 2012
    I have no choice but to believe that ntwari is a good law-abiding citizen. And I also have a commercial radio telephone license. I had a First Class Radio Telephone License and I operated KHOF TV but later my license got downgraded in 1983. What do I have to do to go back into commercial broadcasting?
     
  17. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Well, can you think of any legitimate use for a 40W Broadcast Band FM Transmitter being built from a schematic found on the Internet? As Judge Judy says "Hey! I was born at night... but not last night". ;)

    Regarding your Radio Telephone license.. The FCC didn't downgrade your license. What they did was eliminated 1st Class and 2nd Class license classification. 1st and 2nd Class simply became a Radio Telephone license with no loss of privileges. As far as I know Radar Endorsements are still available with an additional exam.

    I don't think there's anything keeping you from operating a commercial station, other than the fact that most studios no longer house the transmitter or antenna. They sit in remote locations totally unmanned like Repeaters. This put a lot of licensed techs out of jobs.

    Chris
     
    Last edited: Aug 17, 2012
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