EMRFD Message Archive 488

Message Date From Subject
488 2007-02-24 08:57:24 patt896 Reverse Polarity Protection
I've fried more than one piece of gear by applying reverse polarity
battery supply when using snap connectors. I just ran across a
simple device to solve this issue:
"Input Voltage Conditioner - and more - for the FT-817" QST June 2005,
which is happily available as a kit at:
http://www.wulfden.org/ft817.shtml
I plan to add another voltage divider to provide both 9.6 and 12.0 Volt
output.
Dick
489 2007-02-24 11:22:56 larry allen Re: Reverse Polarity Protection
Most, if not all, radios, which operate of d.c. input, use reverse
polarity diode protection...
Larry ve3fxq

----- Original Message -----
490 2007-02-24 13:29:09 patt896 Re: Reverse Polarity Protection
That may be true, Larry, except for KK7B's R? series direct
conversion receivers. Several other kits I've built recently lack
diode protecti
491 2007-02-24 17:49:56 Bart Re: Reverse Polarity Protection
NO, you still wouldn't want to hit it with reverse polarity.  I think Larry was talking about appliance radios that come with a nice warrantee:-)
 
cu, Bart W0IIT
 
492 2007-02-24 18:38:56 brainerd@wildblue... Re: Reverse Polarity Protection
One sure way to prevent reverse polarity on the power supply connection is
to put a full wave bridge in series. This ensures the polarity the radio sees is
always the same even if the supply is reversed. The downside is you have 2
diode voltage drops.

Dave - WB6DHW


On 24 Feb 2007 at 19:49, Bart wrote:

>
> NO, you still wouldn't want to hit it with reverse polarity. I think Larry was talking about appliance
> radios that come with a nice warrantee:-)
>
493 2007-02-24 19:53:41 lmoline@comcast.n... Re: Reverse Polarity Protection
Attachments :
    Hello,

    I have also used a shunt diode with a fuse between the power supply and the diode. This eliminates the voltage drop of a diode in series.

    Loren


    -------------- Original message -------------------
    494 2007-02-24 20:21:20 ted Re: Reverse Polarity Protection
    There is an interesting anti-reverse polarity circuit a
    <http://www.gqrp.com/> Click on the "Tech Info" tab at the top of the
    page and then on "Reverse Polarity Protection" close to the bottom of
    the page.

    Ted
    N3Ted


    On Sat, 2007-02-24 at 18:38 -0800, brainerd@wildblue.net wrote:
    > One sure way to prevent reverse polarity on the power supply
    > connection is
    > to put a full wave bridge in series. This ensures the polarity the
    > radio sees is
    > always the same even if the supply is reversed. The downside is you
    > have 2
    > diode voltage drops.
    >
    > Dave - WB6DHW
    >
    > On 24 Feb 2007 at 19:49, Bart wrote:
    >
    > >
    > > NO, you still wouldn't want to hit it with reverse polarity. I think
    > Larry was talking about appliance
    > > radios that come with a nice warrantee:-)
    > >
    >
    >
    >
    >
    >
    495 2007-02-25 06:25:48 Allison Parent Re: Reverse Polarity Protection
    496 2007-02-25 07:02:28 larry allen Re: Reverse Polarity Protection
    When I was getting onto 2 meter fm, during the early 70's, I went to
    Heathkit to purchase their new hw-202...
    They were just about to ask have me purchase the accompanying power supply
    and I told them that I had the parts to build my own...
    With that, they put a condition on the warrantee that if any problem
    occured that could be considered as a power supply related, my warrantee
    would be reviewed, maybe even voided...
    When I got home, I built the kit.. When the kit was finished I started to
    build my power supply. As I was working on my power supply I tried to
    think of a way to protect my warrantee on the hw-202...
    As I was finishing the power supply, the idea came to me... I put a zener
    diode, about 18 volts, after the line fuse. And then continued with the
    radio...
    A couple years later, I turned on the hw-202. The power supply came on
    but the radio didn't.. I measured the output voltage, of the power supply,
    and it was about 20 plus volts. I imagined that my radio was fried...
    with the 20 plus volts...
    While starting to open my radio, I remembered the zener diode.. I openned
    up the power supply and found that one of the 2n3055's was shorted.. I
    replaced it and measured the output of the power supply.. Now it was 13
    volts ish...
    I replaced the inline fuse and turned the radio on... It worked.... My
    conclusion was that my zener protected my radio from the power supply's
    internal short and resultant high voltage...
    Larry ve3fxq

    ----- Original Message -----
    497 2007-02-25 09:51:53 James Duffey Re: Reverse Polarity Protection
    Ted - Thanks for the posting to the GQRP site, I was going to
    recommend the GQRP site as well:

    < http://www.interalia.plus.com/q_tech12.htm >

    as it has two clever circuits that we don't see much of, including
    the P-MOSFET and a clever relay scheme, as well as a summary of the
    classic diode protection techniques.

    If you use diode protection, Schottky diodes are a good choice as
    they have lower voltage drops than the silicon p-n junction diodes we
    commonly use. - Dr. Megacycle KK6MC/5


    --
    James Duffey KK6MC/5
    Cedar Crest NM 87008
    DM65
    498 2007-03-03 07:46:08 steve SA602 Oscillator Question??

    All

     

    I am playing around with a receiver that uses the SA602 and for the vfo it uses the oscillator in the SA602.  This seems to be quite uncommon, as most designs seem to use a discrete VFO which drives the SA602.  I am wondering why this seems the case in most all designs which use the SA602.  I have seen the internal oscillator used with a crystal for use in a product detector but have only seen one receiver design that uses the oscillator with a LC tank for the a VFO.  Are there some inherent limitations with the oscillator which causes the community to favor external VFO circuits??

     

    Anyone have thoughts or comments on this?

     

    Steve/NU0P

     

    499 2007-03-03 07:55:13 kd5nwa Re: SA602 Oscillator Question??
    What I have read is that it has poor stability.

    At 09:45 AM 3/3/2007, you wrote:
    >All
    >
    >I am playing around with a receiver that uses the SA602 and for the
    >vfo it uses the oscillator in the SA602. This seems to be quite
    >uncommon, as most designs seem to use a discrete VFO which drives
    >the SA602. I am wondering why this seems the case in most all
    >designs which use the SA602. I have seen the internal oscillator
    >used with a crystal for use in a product detector but have only seen
    >one receiver design that uses the oscillator with a LC tank for the
    >a VFO. Are there some inherent limitations with the oscillator
    >which causes the community to favor external VFO circuits??
    >
    >Anyone have thoughts or comments on this?
    >
    >Steve/NU0P
    >
    >
    >----------
    >
    500 2007-03-03 09:06:02 Russ Hines Re: SA602 Oscillator Question??
    The oscillator is on the same substrate as the mixer and I expect that
    could lead to a few unexpected "issues," maybe poor port isolation or
    instability. For a VFO, I'd want access to all the components,
    including the active device, than the internal oscillator would allow.
    Just my two-cents.

    73,
    Russ
    WB8ZCC


    steve wrote:
    > All
    >
    >
    >
    > I am playing around with a receiver that uses the SA602 and for the vfo it
    > uses the oscillator in the SA602. This seems to be quite uncommon, as most
    > designs seem to use a discrete VFO which drives the SA602. I am wondering
    > why this seems the case in most all designs which use the SA602. I have
    > seen the internal oscillator used with a crystal for use in a product
    > detector but have only seen one receiver design that uses the oscillator
    > with a LC tank for the a VFO. Are there some inherent limitations with the
    > oscillator which causes the community to favor external VFO circuits??
    >
    >
    >
    > Anyone have thoughts or comments on this?
    >
    >
    >
    > Steve/NU0P
    >
    >
    501 2007-03-03 14:23:39 jr_dakota Re: SA602 Oscillator Question??
    Mainly so you can drive a receive mixer and a seperate transmit mixer
    from a single VFO, something that's hard, if not impossible to do
    using the internal VFO (Although I have seen it done with a crystal)

    Stabilty shouldn't be a real big problem, the internal transistor has
    both voltage and current regulation that is much better than the
    standard 78xx or zener regulator found in most discrete LOs and is
    quite stable when properly set up, the main problem I've had was
    laying it out so the leads are short yet the inductor is far enough
    away to not get into the inputs and outputs

    One thing that is overlooked with the 602/612 is unbalancing the input
    (Tie pin 1 to ground through a 10k resistor)so the oscillator appears
    on the output pins .... This makes it real easy to make a down and
    dirty test oscillator with a minimum of parts and time ... you can
    also make a heterodyne LO fairly easy but putting a transistor VFO on
    the input and making a crystal oscillator with the internal oscillator
    502 2007-03-03 16:54:47 topossibilities Re: SA602 Oscillator Question??
    I have implemented L/C based VFOs many times using the using the
    on-board oscillator and buffer available at pins 6 and 7.

    In terms of being drifty, given the same L/C components, it is as good
    or better (i.e. operates at micro power levels where the discrete VFO
    may not).

    The easiest design to implement would be the Colpits (where all
    components can be temperture insensitive).

    In terms of everything beinging on the same substrate (and a lot of
    funnies happen)....understand the capabilities of the mixer to begin
    with. You will never see / hear any difference.

    In terms of using it to drive a transmit mixer, it will require a
    simple FET sourse follower buffer (to avoid pull).

    In the case of using the oscillaor functi
    503 2007-03-04 18:37:54 Allison Parent Re: SA602 Oscillator Question??
    504 2007-03-04 20:31:02 steve Re: SA602 Oscillator Question??

    I have noticed that it is not easy to get the 200-300 mv p-p of oscillator signal into the mixer.  I can only get just barely 200mv and am using a 22k resistor from pin 7 to ground to boot.  So I can understand the reasoning why external vfo are being used if this is a common situation.  I find it pretty stable without doing a lot yet to tame its drift with good component selection…I have more problem with getting the bfo oscillator (11.059Mhz Crystal) to give me adequate drive than I do the LC tank 1st mixer circuit.

     

     

    Steve

     

     

     

    505 2007-03-05 11:11:07 Allison Parent Re: SA602 Oscillator Question??