[time-nuts] HP 58516A GPS distribution amplifier information

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Jan 27 19:10:38 UTC 2010 

The trouble with your worst case analysis is that most GPS timing 
receivers actually require a net gain from the antenna to the receiver 
or SVs wont be acquired or tracked.

Bruce

Bob Camp wrote:
> Hi
>
> I agree that in a normal system there likely will be no observable hit at
> all. That would be true with both the active splitter and with the passive
> splitter.
>
> My assumption was that in the absolute worst case, you have used up all of
> the antenna's gain with cable loss. It's only a useful case because that's
> where the splitter is likely to have it's maximum impact. It's likely a case
> where the receiver has given up already....
>
> The basic question is still "what did I get for my money?".
>
> Bob
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of jmfranke
> Sent: Wednesday, January 27, 2010 12:59 PM
> To: 'Discussion of precise time and frequency measurement'
> Subject: Re: [time-nuts] HP 58516A GPS distribution amplifier information
>
> The noise figure hit may be nowhere as bad as 5dB because it depends on the
> noise figure and gain of the antenna preamplifier, not just the noise
> figure.
>
> John WA4WDL
>
> --------------------------------------------------
> From: "Bob Camp"<lists at cq.nu>
> Sent: Wednesday, January 27, 2010 12:34 PM
> To: "'Discussion of precise time and frequency measurement'"
> <time-nuts at febo.com>
> Subject: Re: [time-nuts] HP 58516A GPS distribution amplifier information
>
>    
>> Hi
>>
>> I'm sitting here looking at the spec sheet for the splitter:
>>
>> A normal four way splitter should have a loss of a bit over 6 db.
>>
>> The reason that's bad is that it may degrade the noise figure at your
>> otherwise perfect receiver (and sub 1 db noise figure antenna) by 6 db.
>> (it
>> may also do absolutely nothing bad at all)
>>
>> The splitter has a rated noise figure of 7 db max / 5 db typical.
>>
>> It has a gain that may be a loss of 3 db or a gain of 3 db.
>>
>> Worst case, it's got a -3db gain and a 7 db noise figure. It may degrade
>> the
>> noise figure at the receiver by 10 db. Best case it's got 3 db of gain and
>>      
>    
>> a
>> 5 db noise figure. That's still a noise figure hit of 5 db.
>>
>> All of that is pretty easy to blow holes in as far as a real / normally
>> operating system is concerned. I *think* it's pretty close in the limit
>> case
>> though.
>>
>> If it is close, then the part (yes I bought one to) might improve things
>> by
>> 1 db. It also might degrade things by 4 db under the worst case conditions
>> where it likely matters.
>>
>> Am I missing something here? Obviously it does more than split. It may
>> have
>> better isolation than a conventional splitter. It also has the cute little
>> DC loads in it.
>>
>> Seems like a little bit more RF gain might have been a good idea.
>>
>> Bob
>>
>>
>>
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
>> Behalf Of bg at lysator.liu.se
>> Sent: Wednesday, January 27, 2010 9:41 AM
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] HP 58516A GPS distribution amplifier information
>>
>> Hi,
>>
>> Another option is to remove the DC-block cap on port 1. Then let your
>> primary GPS power the splitter and upstream antenna.
>>
>>     http://www.to-way.com/tf/hp58516a.pdf
>>
>> --
>>
>>    Björn
>>
>>      
>>> Hi
>>>
>>> I found a SMC-BNC adapter of the correct orientation in the bottom of my
>>> junk box. Somehow I doubt I'll ever use it for anything else. BNC cables
>>> and jacks are something I can find easily.
>>>
>>> The top of the unit is held on with screws so getting inside it should
>>> not
>>> be very hard. You could swap the SMC out to something that's more common
>>> for power distribution. Maybe an APC-7 ...
>>>
>>> My guess is they used the SMC because it's unusual. That way you don't
>>> get
>>> a cable with 30 VDC on it hooked where it shouldn't go. If you did run a
>>> 30 volt supply the dc could do some damage. Of course 30 volts on that
>>> unit connected to a "normal" antenna would do some damage as well.
>>>
>>> Bob
>>>
>>>
>>> On Jan 27, 2010, at 1:14 AM, SAIDJACK at aol.com wrote:
>>>
>>>        
>>>> I recommend un-screwing that SMC since it is almost impossible to find
>>>> the
>>>> mate, and feeding two wires from a 5V supply into the unit through the
>>>> hole, and  soldering the wires to the PCB. Works well for me.
>>>>
>>>> bye,
>>>> Said
>>>>
>>>>
>>>> In a message dated 1/26/2010 18:36:18 Pacific Standard Time,
>>>> bruce.griffiths at xtra.co.nz writes:
>>>>
>>>>          
>>>>> I'm  using an HP 58516A GPS distribution amplifier to share my GPS
>>>>> antenna  between my receivers.
>>>>>
>>>>> What is the proper part number or  connector "name"  for the power
>>>>> supply connector  ?
>>>>>
>>>>> Thanks for your help !
>>>>>
>>>>> Claude
>>>>>
>>>>>
>>>>>            
>>>> According to the datasheet option 05 uses an SMC  connector for the
>>>> power.
>>>>
>>>> Bruce
>>>>
>>>>
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>>>
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>>
>>
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