[time-nuts] Re-radiating a GPS signal...??

Said Jackson saidjack at aol.com
Thu Apr 12 16:13:38 UTC 2012


David,

That is correct, the signal is delayed by at least the run length as well. We had to tweak the ublox parameters on our GPSDOs for a particular data center application that used a re-radiator to make it work as the default ublox parameters would get the unit confused due to residual multipath etc.

This is the type of obscure real-world firmware fine-tuning that separates the boys from the men...
One may never need it, but it's good to know its there.

Bye,
Said



On Apr 12, 2012, at 8:11, David McGaw <n1hac at Alum.Dartmouth.ORG> wrote:

> The time/position fix would be from the location of the receiving antenna of the repeater, degraded only by noise.
> 
> This should work if both antennas have good back-side rejection (choke-rings are particularly good for this but perhaps any good timing antenna could meet this), the re-transmitting antenna is close to being directly under the receiving antenna, and the system gain is low enough.  The problem I would see in a room that is not fully shielded is interference between the direct and retransmitted signals at the receiver under test.
> 
> David N1HAC
> 
> On 4/12/12 10:17 AM, MailLists wrote:
>> GPS being extremely time-dependent, any delay introduced will affect positioning precision. Also, the signal is too weak for such an amplification/echo cancelling signal chain.
>> Passive relaying, or using at most a simple amplifier with low enough gain, and short signal delay, remain the only feasible concepts.
>> 
>> On 4/12/2012 4:48 PM, Azelio Boriani wrote:
>>> Passive UHF TV repeaters were in use in Italy too. Nowadays, for the DVB-T
>>> TV, active gap-fillers are used instead. Active gap-fillers are
>>> same-channel repeaters with the necessary, sophisticated echo suppression
>>> technique. We have developed our echo suppression signal processor on a
>>> Xilinx Virtex5 FPGA: maybe something similar may be done for the GPS CDMA.
>>> 
>>> On Thu, Apr 12, 2012 at 3:29 PM, Alan Melia<alan.melia at btinternet.com>wrote:
>>> 
>>>> If the isolation is good and the "clear view" signal is reasonably strong,
>>>> the passive system works well in hangers, metalclad warehouses, ferry lorry
>>>> decks.
>>>> The passive system in the UK used to be refered to as the "Matlock
>>>> Repeater".
>>>> 
>>>> Alan
>>>> G3NYK
>>>> 
>>>> ----- Original Message -----
>>>> From: "Michael Baker"<mpb45 at clanbaker.org>
>>>> To:<time-nuts at febo.com>
>>>> Sent: Thursday, April 12, 2012 2:05 PM
>>>> Subject: [time-nuts] Re-radiating a GPS signal...??
>>>> 
>>>> 
>>>>> Time-nutters--
>>>>> 
>>>>> So--  How do GPS signal re-radiators work?
>>>>> 
>>>>> How do you place a GPS antenna on top of a building,
>>>>> pick up the signal with an LNA, amplify it to re-transmit
>>>>> on an inside antenna without the amplified re-transmitted
>>>>> signal getting back into the roof-top receiving antenna?
>>>>> 
>>>>> I can see circumstances where a huge metal building
>>>>> (aircraft hangar?) might provide enough isolation to
>>>>> prevent problems, but in many cases I wonder about it...
>>>>> ----------------------------
>>>>> 
>>>>> As an aside note-- I recall seeing, many years ago, a totally
>>>>> passive TV signal repeater on top of a tall hill in mountainous
>>>>> territory relaying a TV station signal to some homes in a valley
>>>>> just below.  The passive repeater consisted of an array of
>>>>> high-gain UHF yagis pointing to the 40 mile distant TV station tower.
>>>>> The yagi array was coupled to another set of high-gain yagi
>>>>> antennas pointing down to the homesites in the valley.  I was
>>>>> told that it worked pretty well.
>>>>> 
>>>>> Mike Baker
>>>>> ----------------------
>>>>> 
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