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

[jmfranke]

David's comment on the direct and retransmitted signals is right on point. 
You are creating a multipath environment with increased signal strength and 
matching polarization. Even with no amplification between the antennas, you 
are generating multipath signals for you and your neighbors.

Advocating signal repeaters is very dangerous. With out proper bandpass 
filtering and path isolation you are inviting trouble from feedback 
oscillation, both in-band and out of band. You may not even be aware of out 
of band effects. If not done properly, including taking in account seasonal 
variation of vegetation, possible effects of someone moving lawn furniture 
around or even vehicular motion changing the feedback path, the results 
could be disastrous. You could be the owner of an intermittent jammer, 
interfere with GPS and/or other signals, and possibly receive a visit from 
the authorities. Look at the problems that where caused by oscillating TV 
peamplifiers radiating from a marina on the west coast. Retransmitting with 
a different output frequency is a different issue and may be a better 
approach.

John  WA4WDL

--------------------------------------------------
From: "David McGaw" <n1hac at Alum.Dartmouth.ORG>
Sent: Thursday, April 12, 2012 11:11 AM
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Subject: Re: [time-nuts] Re-radiating a GPS signal...??

> 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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