[DSP-10] No TX: from frying pan to fire

Sun, 25 Aug 2002 10:21:06 +0000

I assume replacement of the MMIC's should not be critical as long as you
put in one that has the ability to handle the power level you are looking at 
so it will not clip or compress. The gain should also be approx the same at 
2 meter. You might have to tewak some of the resistor values to achieve the 
proper biasing. Consult the datasheet if it is not a direct replacement.

I also had to do a replacement i thaught, but later found out that the MMIC 
that I thought I had grilled was OK.

73 de la9eea

>From: "Rajiv Dewan, N2RD" <[email protected]>
>Reply-To: [email protected]
>To: <[email protected]>
>Subject: [DSP-10] No TX: from frying pan to fire
>Date: Sat, 24 Aug 2002 17:34:27 -0000
>
>Previously:
>This is a follow up on the "No TX out" story.  Essentially, receiver
>works great but no there is TX power out that I can measure using the
>RF probe built as described.  The DC voltages in the TX section WERE
>OK.
>
>Now:
>I do not have a means of generating small signals at 144Mhz so I
>hooked up my 2m HT to a 2GHz Sampling directional coupler.  This
>seemed to generate a very tiny output that was not measurable using
>the RF probe and my voltmeter.
>
>I fed the weak singal into input of U4 to no effect. When I fed this
>into U5 input, the S meter on the frequency counter hooked to output
>jumped full scale reading.  This seemed to indicate that U4 was bad.
>
>I removed the small signal input and re-checked the DC voltages around
>U4.  To my surprise I found that now the DC voltages, that had
>previously been fine,  were now incorrect.  Voltage at pin3, which I
>had previously measured to be 3.6V, was now 7.55V.  Pin 1 was at 0V -
>also incorrect.  So essentially the device DC current had fallen from
>a proper value of 31ma to 10ma.  I guess, somehow, in all my fiddling
>I have destroyed U4  MSA-0686.  Ouch!
>
>So I now have to acquire a MAR-6 mmic and go from there.
>
>Any thoughts?
>
>Regards,
>
>
>- -
>Rajiv Dewan, N2RD
>-----------------------
>I regret that I do not accept any e-mail from:
>  yahoo.com, msn.com, hotmail.com, lycos.com and excite.com
>  because of excessive spam mail from these domains.
>---------------------------
>
>
>
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