[time-nuts] HP58504A antenna
jpradoes at telefonica.net
Tue Jul 22 16:19:57 EDT 2008
Thank you very much Bruce and all who replied my previous message,
According to measurements made with multimeter I think the MMIC is damaged,
because it´s consuming more than 10mA, when its maximum specified current,
at 3V, is 8mA, and the typical 6mA; maybe some of its internal transistors
are shorted. The measured supply voltage at pin 6, mid point of 270 and 68
ohms resistors, is 2.78V.
The input transistor is supplied with 2.61V and biased with 0.69V, the
current is 8mA, so I think it´s OK.
By the way, my Z3801 only delivers 4.67V to the antenna connector.
Datasheet of the MMIC can be seen here:
Now my problem is where to purchase one of these devices ;-)
Best regards....José, EA1PX
----- Original Message -----
From: "Bruce Griffiths" <bruce.griffiths at xtra.co.nz>
To: "Discussion of precise time and frequency measurement"
<time-nuts at febo.com>
Sent: Tuesday, July 22, 2008 7:44 AM
Subject: Re: [time-nuts] HP58504A antenna
> Resistor values used are probably:
> 100 = 10 ohms
> 560 = 56 ohms or is it 680 = 68 ohms?
> 101 = 100 ohms
> 121 = 120 ohms
> 181 = 180 ohms
> 221 = 220 ohms
> 271 = 270 ohms
> Thus the total resistance from the 5V supply to the output terminal of
> the input device is actually = 220 + 10 + 10 = 240 ohms.
> Equivalent resistance from input device "source" terminals to ground =
> 90 ohms.
> Voltage divider for Vcc of MMIC is 56 ohms from 5V is series with 270
> ohms to ground nominal current ~ 15mA + 6mA? for MMIC, total ~ 21mA.
> Input device if shorted would have a current drain of 5V/(90+220 + 10 +
> 10) ~ 15mA.
> Thus measuring the dc output of the input device and/or measuring its
> power supply current is required to assist diagnosis.
> Some pHEMT devices have an absolute drain source voltage limit as low as
> 3V so the operating drain source voltage of the input device may only be
> 1/2 that.
> Typical MMICs have a somewhat larger dc voltage on the output.
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