[time-nuts] Z3816A alarm

Javier javier at nebulosa.org
Sat Jan 22 06:38:03 EST 2005


Hello,

The Z8316 uses a Motorola M8 Oncore GPS receiver, that is the one who 
embodies the antenna current info in the status word in the data 
messages. If I'm right, the 'good' values for antenna current are 
between 15 and 80 mA. Values both under and over these cause a 
under-current or over-current flagging, so the selected resistor for 
current drawing should be selected not to draw more than 15mA so the 
alarm works if the antenna really becomes open, so 680 ohms seem to be 
and adequate value.

Best regards,

Javier, EA1CRB
www.hvsistemas.es

Bill Jones, K8CU wrote:

>Rex,
>
>Searching the Z3801A forum with the phrase "Z3816A alarm" results in a
>resistor work-around much like you have already described.
>
>I am not aware of a way to actually disable the low current alarm.
>
>Bill Jones, K8CU
>www.realhamradio.com
>
>
>----- Original Message ----- 
>From: "Rex" <rexa at sonic.net>
>To: "Discussion of precise time and frequency measurement"
><time-nuts at febo.com>
>Sent: Saturday, January 22, 2005 4:21 AM
>Subject: Re: [time-nuts] Z3816A alarm
>
>
>On Sat, 22 Jan 2005 01:09:34 -0000, "Bill Jones, K8CU"
><k8cu at realhamradio.com> wrote:
>
>  
>
>>Rex,
>>
>>Unlike the Z3801A, the Z3816A has an alarm specific for the antenna.  I
>>suggest that you view a thread on my site that describes this condition as
>>well as a work-around for it:
>>http://realhamradio.com/cgi-bin/yabb/YaBB.cgi?board=1;action=display;num=10
>>    
>>
>3696003;start=4
>  
>
>>Bill Jones, K8CU
>>    
>>
>
>Thanks, Bill and Brooke,
>
>You were correct. The problem is that the 2nd antenna does not draw
>enough current. This one has slightly better signal than the HP antenna,
>so it is too bad that it draws too little current to satisfy the Z3816A.
>
>I verified by causing the "problem" antenna to draw more current. I
>found an N bias-T with no DC blocking and put it in series with the
>antenna. The signal was still there and alarm still on. Then I added a
>620 ohm resistor across the bias-T DC input port to make the cable draw
>about 8 mA more. Alarm went out and antenna still works.
>
>Frustrating that the error status register does not indicate this
>condition. Seems like there ought to be some way to view status that
>indicates this error condition is what is causing the alarm.
>
>Bill, you mentioned a workaround, but I didn't see any in the thread you
>referenced. Is there some way to disable the low current alarm?
>
>Anyway, thanks for pointing me at the problem.
>
>-Rex
>
>
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