[time-nuts] GPS splitter
magnus at rubidium.dyndns.org
Fri Jun 23 02:54:05 EDT 2017
I don't remember anymore. I just picked one somewhere in that range. I
got a inductor SMD set. The main point is that the time-constant of L*R
needs to be low enough not to cause any real harm to 1,57542 GHz, which
makes the value relatively flexible. Sure, I did not consider the stub
of the T-connector, but it seemed to work.
So, 68 nH could very well be it.
On 06/21/2017 08:12 PM, David C. Partridge wrote:
> Hi Magnus - what sort of inductor value did you use? 68nH or so?
> -----Original Message-----
> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Magnus Danielson
> Sent: 17 June 2017 15:12
> To: time-nuts at febo.com
> Cc: magnus at rubidium.se
> Subject: Re: [time-nuts] GPS splitter
> At one time I had to design a DC-load since the GPSDO did not experience enough antenna current due to a different antenna being used. So, a BNC-T was quickly converted with a SMD inductor and resistor to add 150 Ohm of more load, and that helped the telecom operator to get their GPS out of "no GPS antenna" warning and actually accept the GPS satellites it was already detecting fine.
> On 06/17/2017 02:40 PM, Bob kb8tq wrote:
>> The DC block requirement depends a lot on the design of the GPSDO’s
>> you are using. With some GPSDO’s a 50 ohm load on the eighth port of a
>> splitter will do a pretty good job of “antenna detect” signaling. In
>> the more general case of “I didn’t design this beast” dc blocks and dc shunts to ground is the best approach.
>> This fairly quickly gets you headed in the direction of the HP /
>> Symmetricom splitters.
>>> On Jun 16, 2017, at 11:54 PM, Clay Autery <cautery at montac.com> wrote:
>>> This brings up some interesting questions:
>>> If sharing an active GPS antenna, do you have to DC block all but one
>>> receiver port to prevent multiple receivers trying to supply current
>>> to the antenna?
>>> On say a 26dB antenna (ignoring line loss, power divider insertion
>>> loss, et al), what is the effective gain to each receiver? (Sorry,
>>> having a senior moment)
>>> Should ALL unused ports have 50 ohm +/- 0j terminators on them? I
>>> assume so... Thus, it would be "better" to always use the divider
>>> with the minimum required ports?
>>> I am assuming since this is a receive only situation, it will follow
>>> approximately the same rules of physics that dealing with satellite
>>> antenna installations.
>>> I would LIKE to share one PC-TEL 26dB GPS antenna mounted at the top
>>> of my 38 foot horiz.loop mast right at the shack entrance, using
>>> LMR-400-DB from antenna to Narda 2-way and thence to my current
>>> hacked Nortel GPSDO and my soon to be complete RPi 2/3 w/ Adafruit
>>> Ultimate GPS Hat NTP Server. On that mast, the antenna would have a
>>> near 360 degree view of the sky completely unobstructed.
>>> (Eventually, I expect both of those units to be replaced with commercial units).
>>> I'm assuming that I DC block whichever unit is capable of providing
>>> the LEAST current at 5VDC... I suspect the Nortel unit can supply
>>> more current than the RPi, but that's not a guarantee... And I guess
>>> I could block/turn off DC delivery on BOTH units and add a voltage
>>> adjustable, current limiting DC injection unit into the line.
>>> Clay Autery, KY5G
>>> MONTAC Enterprises
>>> (318) 518-1389
>>> On 6/16/2017 7:26 PM, Tim Lister wrote:
>>>> On Fri, Jun 16, 2017 at 4:40 PM, Gregory Beat <w9gb at icloud.com> wrote:
>>>>> I have reached the point that I need a 4-port splitter for my GPS antenna (outdoor 5 volt). Any recommendations of models (HP/Symmertricom/Microsemi) to acquire OR to avoid??
>>>> As we recommended to me when I asked a similar question, the Narda
>>>> 4372A-4 was a brand I had not heard of before and didn't come up in
>>>> 'gps splitter' searches. I got one on ebay for $24 plus a bit extra
>>>> for DC blocks on the n-1 other ports and it seems to work well and
>>>> it was handy to have an SMA-based solution as most of the gps
>>>> receivers and the antenna pucks seem to use SMA. This meant I only
>>>> needed 1 N to SMA converter cable for an external antenna (which has
>>>> yet to be externalized...). I found it smaller in real life than it
>>>> looks in a lot of the pictures, about the size of a modern
>>>> smartphone but about double or more the thickness (the connectors are on the ends).
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