Re: [time-nuts] eBay GPS antenna test results.

[Bob kb8tq]

Hi

As with any antenna mods, the issue isn’t so much doing them as proving that
what you did had this or that effect. A lot of what you are paying for on the 
fancy
antennas is the fact that indeed they went through some sort of validation 
process
on top of the design process. 

An equally valid point is that the standard “telecom” antennas likely are no 
great
thing for low angle multi path either. That is one of several reasons we tend 
to 
like cranking up the elevation mask on our TBolts. 

If you are going for the “I want something that does it all” approach. You 
would want
an antenna that does at least L1 / L2 / L5 and covers the GPS and Glonas parts 
of 
the bands. So far, those have not shown up as $100 new in box items ….. Given
that the price of gear covering all of that is still “a bit high” (even as a 
home brew 
SDR), I’m not sure it matters a whole lot at this point. 

Bob

> On Feb 15, 2018, at 9:13 AM, jimlux  wrote:
> 
> On 2/15/18 6:04 AM, Bob kb8tq wrote:
>> Hi
>> There are a number of reasons to believe that these antennas are worse
>> than the typical “telecom GPS” antenna for L1 only duty driving a TBolt.
>> If you are going to do L1 / L2 work with something like a NetRS, then indeed
>> you will need a dual band antenna. These (the $99 ones)  are the lowest cost
>> “new in box” L1 / L2 antennas that I have seen. One would *guess* that their
>> close to horizon multi path rejection is not quite as good as a Trimble 
>> Zephyr,
>> a Novatel Pinwheel, or a choke ring. The ones from China
>>  also don’t cost $1800 to $6000 when new either …
> 
> 
> one could probably improvise something that serves as a choke ring, or 
> elevation fence.  The infamous JPL Helibowl is pretty simple, and has pretty 
> good rejection of signals near the horizon.
> 
> See, e.g. Page 143 in GPS/GNSS Antennas, by Rao.  (I found it on google
> 
> https://books.google.com/books?id=nL-YFWLQrPIC=PA143=PA143=helibowl+antenna=bl=U-7Y3TMIQw=D4xZVMmv73XkCAH_8KkMegMnxX4=en=X=0ahUKEwjbjLGTjKjZAhVM7WMKHdYPC5sQ6AEIMTAB#v=onepage=helibowl%20antenna=false
> 
> Oddly, it cites to C.Y Cheng, Numerical Electromagnetic Modeling of a Small 
> Aperture Helical-Fed Reflector Antenna, Masters thesis, Ohio University, Aug 
> 1998.
> 
> Good luck finding that one on-line
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Re: [time-nuts] eBay GPS antenna test results.

[jimlux]

On 2/15/18 6:04 AM, Bob kb8tq wrote:

Hi

There are a number of reasons to believe that these antennas are worse
than the typical “telecom GPS” antenna for L1 only duty driving a TBolt.
If you are going to do L1 / L2 work with something like a NetRS, then indeed
you will need a dual band antenna. These (the $99 ones)  are the lowest cost
“new in box” L1 / L2 antennas that I have seen. One would *guess* that their
close to horizon multi path rejection is not quite as good as a Trimble Zephyr,
a Novatel Pinwheel, or a choke ring. The ones from China
  also don’t cost $1800 to $6000 when new either …




one could probably improvise something that serves as a choke ring, or 
elevation fence.  The infamous JPL Helibowl is pretty simple, and has 
pretty good rejection of signals near the horizon.


See, e.g. Page 143 in GPS/GNSS Antennas, by Rao.  (I found it on google

https://books.google.com/books?id=nL-YFWLQrPIC=PA143=PA143=helibowl+antenna=bl=U-7Y3TMIQw=D4xZVMmv73XkCAH_8KkMegMnxX4=en=X=0ahUKEwjbjLGTjKjZAhVM7WMKHdYPC5sQ6AEIMTAB#v=onepage=helibowl%20antenna=false

Oddly, it cites to C.Y Cheng, Numerical Electromagnetic Modeling of a 
Small Aperture Helical-Fed Reflector Antenna, Masters thesis, Ohio 
University, Aug 1998.


Good luck finding that one on-line
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Re: [time-nuts] eBay GPS antenna test results.

[Bob kb8tq]

Hi

There are a number of reasons to believe that these antennas are worse
than the typical “telecom GPS” antenna for L1 only duty driving a TBolt. 
If you are going to do L1 / L2 work with something like a NetRS, then indeed
you will need a dual band antenna. These (the $99 ones)  are the lowest cost 
“new in box” L1 / L2 antennas that I have seen. One would *guess* that their
close to horizon multi path rejection is not quite as good as a Trimble Zephyr,
a Novatel Pinwheel, or a choke ring. The ones from China
 also don’t cost $1800 to $6000 when new either …

Bob

> On Feb 15, 2018, at 4:31 AM, Christoph Kopetzky  wrote:
> 
> Moin,
> are in the meantime any experiences with these gps antennas from the china 
> seller (ms_geo)?
> I found two type of them from the same seller:
> 
> 1) 
> https://www.ebay.com/itm/High-Precision-L1-L2-GNSS-GPS-GLONASS-BeiDou-RTK-CORS-survey-antenna/162718512935?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649
>  
> 
> this one is the 3.3 - 18 V version with 5 dB antenna gain and 42 dB LNA gain 
> for  appr. 100 US$
> 
> and 
> 
> 2) 
> https://www.ebay.com/itm/High-Precision-GNSS-GPS-GLONASS-BeiDou-RTK-CORS-survey-machine-control-antenna/162710405447
>  
> 
> this one has 3.3 - 10 V  voltage requirement and nearly the same gain values 
> but 85 US$ 
> 
> Does anyone have one oth them up and running?
> 
> Are they much more better as a Symmetricom 58532A antenna ore the puck head 
> variant?
> 
> If yes I would give it also a try but the shipment time from goods from china 
> are very high. Here to Germany there are timeframes from four to eight weeks 
> normal. :(
> 
> But the price 
>  -
> Chris
> Am 13.02.2018 um 03:05 schrieb Bob kb8tq:
>> Hi
>> 
>> Sitting here casually reading the data sheets for some of the modern Trimble
>> survey receivers - they have gone to 7.2V (just below your 7.5V trigger 
>> point) 
>> as an antenna supply voltage. 
>> 
>> Who knows what that might imply relative to this antenna. 
>> 
>> Bob
>> 
>>> On Feb 11, 2018, at 12:44 PM, John Green  
>>>  wrote:
>>> 
>>> They have issued a refund. The seller said that my antenna was defective.
>>> This is kind of a strange outfit. They are in Russia selling Chinese goods,
>>> shipped from China.  Since I don't have to return it, I will disassemble it
>>> to see what went bad. I replied that if he could assure me that it would
>>> work on 12 volts, I might order another.
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Re: [time-nuts] eBay GPS antenna test results.

[Clay Autery]

I would be extremely surprised if ebay does not rule in your favor.
I've only had ONE case EVER opened against me, and it was CLEARLY not a 
valid case, but eBay still made me give the buyer his money back IN FULL 
to include shipping.

eBay almost always picks the buyer over the seller.

73,
Clay, KY5G


On 02/11/18 08:07, John Green wrote:

I opened a "Not as listed" case and heard back from the seller. They said
that the antenna is definitely 3.3 to 18 volts and have sold several that
are in operation. They wanted to know specifically how I tested the
antenna, why I thought it shorted, and if I actually ever hooked it to a
GPS receiver. I answered as best I could but haven't heard anything
further. eBay seems to like pictures or videos. Though problematic, I
suppose I could take some pictures. I offered to do so in my response to
the seller. They do seem a bit more responsive to buyer complaints than in
previous years. I recently ordered a 64 Gb micro SD card from a US based
seller. I got a message from eBay stating that they had removed the listing
but that everything should be OK. I never received the SD card, and after a
month, checked PayPal and saw that I had been charged for it. I contacted
eBay and they refunded my money the next day.
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Re: [time-nuts] eBay GPS antenna test results.

[Bob kb8tq]

Hi

Sitting here casually reading the data sheets for some of the modern Trimble
survey receivers - they have gone to 7.2V (just below your 7.5V trigger point) 
as an antenna supply voltage. 

Who knows what that might imply relative to this antenna. 

Bob

> On Feb 11, 2018, at 12:44 PM, John Green  wrote:
> 
> They have issued a refund. The seller said that my antenna was defective.
> This is kind of a strange outfit. They are in Russia selling Chinese goods,
> shipped from China.  Since I don't have to return it, I will disassemble it
> to see what went bad. I replied that if he could assure me that it would
> work on 12 volts, I might order another.
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[time-nuts] eBay GPS antenna test results.

[John Green]

They have issued a refund. The seller said that my antenna was defective.
This is kind of a strange outfit. They are in Russia selling Chinese goods,
shipped from China.  Since I don't have to return it, I will disassemble it
to see what went bad. I replied that if he could assure me that it would
work on 12 volts, I might order another.
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Re: [time-nuts] eBay GPS antenna test results.

[Bob kb8tq]

Hi

Well, good news / bad news I guess. The seller is at least responding to your
input. They also did not come back with something about “there is no voltage
spec”. It’s quite possible that they are the 5th person in a chain of sellers 
and
a substitution got made (unknown to them) at seller 3. 

I’d hook up a power supply, a current meter and a couple of clip leads. Shoot a
cell phone picture at 5V and one a second one at 10V. That’s all it should 
take. 
If you have more than one DVM, that would make things even more clear. 

Bob

> On Feb 11, 2018, at 9:07 AM, John Green  wrote:
> 
> I opened a "Not as listed" case and heard back from the seller. They said
> that the antenna is definitely 3.3 to 18 volts and have sold several that
> are in operation. They wanted to know specifically how I tested the
> antenna, why I thought it shorted, and if I actually ever hooked it to a
> GPS receiver. I answered as best I could but haven't heard anything
> further. eBay seems to like pictures or videos. Though problematic, I
> suppose I could take some pictures. I offered to do so in my response to
> the seller. They do seem a bit more responsive to buyer complaints than in
> previous years. I recently ordered a 64 Gb micro SD card from a US based
> seller. I got a message from eBay stating that they had removed the listing
> but that everything should be OK. I never received the SD card, and after a
> month, checked PayPal and saw that I had been charged for it. I contacted
> eBay and they refunded my money the next day.
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[time-nuts] eBay GPS antenna test results.

[John Green]

I opened a "Not as listed" case and heard back from the seller. They said
that the antenna is definitely 3.3 to 18 volts and have sold several that
are in operation. They wanted to know specifically how I tested the
antenna, why I thought it shorted, and if I actually ever hooked it to a
GPS receiver. I answered as best I could but haven't heard anything
further. eBay seems to like pictures or videos. Though problematic, I
suppose I could take some pictures. I offered to do so in my response to
the seller. They do seem a bit more responsive to buyer complaints than in
previous years. I recently ordered a 64 Gb micro SD card from a US based
seller. I got a message from eBay stating that they had removed the listing
but that everything should be OK. I never received the SD card, and after a
month, checked PayPal and saw that I had been charged for it. I contacted
eBay and they refunded my money the next day.
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Re: [time-nuts] eBay GPS antenna test results.

[Bob kb8tq]

Hi

Ok, the antenna in the pictures on the listing *does* have labeling in English 
and it sure looks like it says 3.3 to 18V on the antenna. Certainly you have 
(and the rest of us may soon have) a case for “not as shown” in terms of 
what you got (and we get).

Bob

> On Feb 9, 2018, at 9:31 PM, John Green  wrote:
> 
> Bob wrote:
> Is it labeled 3.3 to 18V on the antenna?
> 
> No, the writing on the antenna is all Chinese. The specs published on eBay
> state that it is.
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[time-nuts] eBay GPS antenna test results.

[John Green]

Bob wrote:
Is it labeled 3.3 to 18V on the antenna?

No, the writing on the antenna is all Chinese. The specs published on eBay
state that it is.
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Re: [time-nuts] eBay GPS antenna test results.

[Dana Whitlow]

I would surmise that the antenna has (or rather had) a protection network
to protect against voltage spikes or surges.  Your description of events
seems consistent with an triggered SCR crowbar circuit, and the 2nd
attempt at the higher current limit shorted the SCR.  Note that this may
not have been a regular SCR, but perhaps a NPN/PNP pair hooked up
to emulate an SCR.   If you can find evidence of such a circuit, it may
be replaceable or simply removable, leaving the antenna fully functional.

Assuming this works, do keep the supply voltage down to something
reasonable like 5 or 6 volts.   Excess voltage will result in unneeded
heat generation in whatever regulator the antenna uses, shortening
its life.

Dana



On Fri, Feb 9, 2018 at 5:00 PM, Dr. David Kirkby <
drkir...@kirkbymicrowave.co.uk> wrote:

> On 9 February 2018 at 21:43, John Green  wrote:
>
> > To those who doubted that the antenna was actually a 3.3 to 18 volt
> design,
> > it seems you were correct. Today, I hooked it up to a variable power
> supply
> > and slowly raised the DC voltage fed to the antenna. It began to pull
> > current at about 2.9 volts and at 3.3 volts, took about 40 mA. I
> continued
> > to slowly raise the voltage. At about 7.5 volts, the current suddenly
> > dropped to 10 mA. At just below 12 volts, it suddenly increased to 80 mA
> > and the supply went into current limit. I increased the current limit to
> > 130 mA and repeated the exercise. Everything went as above until I
> reached
> > 12 volts and the current went to 130 mA and the supply went into current
> > limit. Lowering the voltage didn't lower the current. I disconnected it,
> > waited a minute, and tried again. Yep, shorted. It would have worked well
> > with the T bolt, but would have blown anyway if I tried to use it with my
> > 12 volt supply and bias T. I guess I will get inside it somehow to see if
> > it can be repaired. My first attempt ended in failure. I guess I need a
> > bigger screwdriver with which to pry the top off. I am going to contact
> the
> > seller and tell them it was not as advertised. I kind of doubt that will
> > get me anything, but it won't hurt to try. There is a saying about
> > experience being a cruel teacher. You get the results first, and the
> lesson
> > after. Oh well.
> >
>
>
> You should not open it up, but open an eBay case for item not as described.
> If it said it would do 3-18 V, but does not, then its not as described, and
> you should get your money back. The chances are the seller will not want to
> arrange collection, so you will probably get to keep it anyway. But you
> should get a refund before opening it up.
>
> Dave
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Re: [time-nuts] eBay GPS antenna test results.

[Dr. David Kirkby]

On 9 February 2018 at 21:43, John Green  wrote:

> To those who doubted that the antenna was actually a 3.3 to 18 volt design,
> it seems you were correct. Today, I hooked it up to a variable power supply
> and slowly raised the DC voltage fed to the antenna. It began to pull
> current at about 2.9 volts and at 3.3 volts, took about 40 mA. I continued
> to slowly raise the voltage. At about 7.5 volts, the current suddenly
> dropped to 10 mA. At just below 12 volts, it suddenly increased to 80 mA
> and the supply went into current limit. I increased the current limit to
> 130 mA and repeated the exercise. Everything went as above until I reached
> 12 volts and the current went to 130 mA and the supply went into current
> limit. Lowering the voltage didn't lower the current. I disconnected it,
> waited a minute, and tried again. Yep, shorted. It would have worked well
> with the T bolt, but would have blown anyway if I tried to use it with my
> 12 volt supply and bias T. I guess I will get inside it somehow to see if
> it can be repaired. My first attempt ended in failure. I guess I need a
> bigger screwdriver with which to pry the top off. I am going to contact the
> seller and tell them it was not as advertised. I kind of doubt that will
> get me anything, but it won't hurt to try. There is a saying about
> experience being a cruel teacher. You get the results first, and the lesson
> after. Oh well.
>


You should not open it up, but open an eBay case for item not as described.
If it said it would do 3-18 V, but does not, then its not as described, and
you should get your money back. The chances are the seller will not want to
arrange collection, so you will probably get to keep it anyway. But you
should get a refund before opening it up.

Dave
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Re: [time-nuts] eBay GPS antenna test results.

[Bob kb8tq]

Hi

Is it labeled 3.3 to 18V on the antenna?

Bob

> On Feb 9, 2018, at 4:43 PM, John Green  wrote:
> 
> To those who doubted that the antenna was actually a 3.3 to 18 volt design,
> it seems you were correct. Today, I hooked it up to a variable power supply
> and slowly raised the DC voltage fed to the antenna. It began to pull
> current at about 2.9 volts and at 3.3 volts, took about 40 mA. I continued
> to slowly raise the voltage. At about 7.5 volts, the current suddenly
> dropped to 10 mA. At just below 12 volts, it suddenly increased to 80 mA
> and the supply went into current limit. I increased the current limit to
> 130 mA and repeated the exercise. Everything went as above until I reached
> 12 volts and the current went to 130 mA and the supply went into current
> limit. Lowering the voltage didn't lower the current. I disconnected it,
> waited a minute, and tried again. Yep, shorted. It would have worked well
> with the T bolt, but would have blown anyway if I tried to use it with my
> 12 volt supply and bias T. I guess I will get inside it somehow to see if
> it can be repaired. My first attempt ended in failure. I guess I need a
> bigger screwdriver with which to pry the top off. I am going to contact the
> seller and tell them it was not as advertised. I kind of doubt that will
> get me anything, but it won't hurt to try. There is a saying about
> experience being a cruel teacher. You get the results first, and the lesson
> after. Oh well.
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Re: [time-nuts] eBay GPS antenna test results.

[John Green]

To those who doubted that the antenna was actually a 3.3 to 18 volt design,
it seems you were correct. Today, I hooked it up to a variable power supply
and slowly raised the DC voltage fed to the antenna. It began to pull
current at about 2.9 volts and at 3.3 volts, took about 40 mA. I continued
to slowly raise the voltage. At about 7.5 volts, the current suddenly
dropped to 10 mA. At just below 12 volts, it suddenly increased to 80 mA
and the supply went into current limit. I increased the current limit to
130 mA and repeated the exercise. Everything went as above until I reached
12 volts and the current went to 130 mA and the supply went into current
limit. Lowering the voltage didn't lower the current. I disconnected it,
waited a minute, and tried again. Yep, shorted. It would have worked well
with the T bolt, but would have blown anyway if I tried to use it with my
12 volt supply and bias T. I guess I will get inside it somehow to see if
it can be repaired. My first attempt ended in failure. I guess I need a
bigger screwdriver with which to pry the top off. I am going to contact the
seller and tell them it was not as advertised. I kind of doubt that will
get me anything, but it won't hurt to try. There is a saying about
experience being a cruel teacher. You get the results first, and the lesson
after. Oh well.
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