[问答]

如何用前置放大器和滤波器测量GPS天线的延迟？

问答对人有帮助，内容完整，我也想知道答案 0 特殊的GPS灵感器针对定时应用进行了优化，因此可以连接到计算机来制作NTP服务器。这些信息通常用于在实验室中提供准确的10 MHz频率参考。它们应配备一个外部有源天线，从反射中清除，以获得最佳效果。这些定时接收器具有设置GPS接收器和天线之间的延迟的功能，以便接收器准确地知道时间。如何衡量GPS天线和天线电缆末端之间的延迟？显然，人们可以通过其长度和速度因子粗略估计同轴电缆的延迟，但速度因子从未非常准确地知道。但是天线将有一个集成的前置放大器和SAW滤波器，中心位于1575 MHz左右，因此仅测量同轴电缆是不够的。我认为可以做一个简单的偶极子，从VNA的端口1激发并测量S21。人们可以很容易地计算出两个天线之间的延迟，但是我不清楚当滤波器具有以1575 MHz为中心的窄带宽时如何测量延迟 - 当可用带宽很大时，只能使用时域选项狭窄。可以使用端口扩展吗？我怀疑没有，因为他们认为延迟是50欧姆传输线的延迟，而不是尖锐的滤波器。我怀疑VNA是正确的工具，但我无法弄清楚如何正确地做到这一点。典型的电缆可能是20米，因此有许多波长。戴夫以上来自于谷歌翻译以下为原文 Special GPS reveivers are optimised for timing applications, so can be hooked up to a computer to make an NTP server. Such reveivers are often used to provide an accurate 10 MHz frequency reference in a lab to. They should be fitted with an outside active antenna clear from reflections for best results. These timing receivers have the facility to set the delay between the GPS receiver and the antenna so that the receiver knows the time accurately. How could one measure the delay between the GPS antenna and the end of the antenna cable? Obviously one could do a rough estimate of the delay of the coax by its length and velocity factor, but the velocity factor is never known very accurately. But the antenna will have an integrated pre-amp and SAW filter centred around 1575 MHz, so just measuring the coax is not enough. I considered one could make a simple dipole, excite that from port 1 of the VNA and measure S21. One could easily calculate the delay between the two antennas, but it is not clear to me how to measure the delay when the filter will have a narrow bandwidth centred around 1575 MHz - one cant simply use the time domain option when the usable bandwidth is very narrow. Could one use port extension? I suspect not, as they assume that the delay is that of a 50 Ohm transmission line, not a sharp filter. I suspect a VNA is the right tool for this, but I can't work out how to do it properly. A typical run of cable maybe 20 m, so is many wavelengths. Dave 0
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答案对人有帮助，有参考价值 0 您走在正确的轨道上，但我认为您可以使用偶极天线和GPS有源/滤波天线进行群延迟测量。你必须考虑过滤器是对的。你知道滤波器的带宽吗？滤波器的群延迟大约为N / BW，其中N是部分的数量，BW是带宽，因此100 MHz 3部分滤波器将具有30 nsec的延迟。您可以看到这完全淹没了电缆或偶极子的延迟，因此我首先进行此测量，看看原始整体延迟是多少。通过原始测量，我的意思是使用同轴电缆连接您的VNA并进行通过标准化。然后使用S21和延迟格式将电缆连接到偶极天线和GPS天线并测量总延迟。如果它与物理长度相比非常长，那么您可以怀疑过滤器是导致延迟的一个重要原因。您希望实现的延迟准确度是多少？使用这种方法，1 nsec是合理的，但如果你需要100 psec或10 psec，那么我们必须要小心。以上来自于谷歌翻译以下为原文 You are on the right track, but I think you can simply do a group delay measuerment using your dipole antenna and the GPS active/filtered antenna. You are right that you must account for the filter. Do you know the bandwidth of the filter? The group delay of filters is approximately N/BW where N is the number of sections and BW is the Bandwidth, so a 100 MHz 3 section filters will have 30 nsec of delay. You can see that this completely swamps the delay of the cable or the dipole, so I would first make this measurement and see what the raw overall delay is. By raw measurement I mean take your VNA with coax cables and do a thru normalization. then connect the cables to the dipole and GPS antenna and measure the overall delay, using S21 and the delay format. If it is very long compared to the physical length then you can suspect your filter is a large cause of the delay. What is the level of delay accuracy you are looking to achieve. With this method, 1 nsec is reasonable, but if you need 100 psec or 10 psec, then we will have to be much more careful.

2018-11-1 11:53:43 评论举报孔德羲

答案对人有帮助，有参考价值 0 嗨乔尔，我刚刚注意到你的回复，所以请原谅延迟回复。我实际上并不想自己做测量，但我在时间坚果邮件列表上看到了问题。该列表由那些非常精确地测量时间和频率的人阅读。设置列表的人有一块手表，每天只能保持几秒钟，但电池寿命只有45分钟。 http://leapsecond.com/pages/atomic-bill/运行该列表的Tom在他的网站上有一些很棒的东西，包括他的国际象棋，所有RF工程师都应该对它有所了解。他已经将几个HP铯钟带到山上进行实验。我怀疑20％的人阅读时间坚果个人拥有至少一个铯频率标准，至少有一个人拥有自己的氢脉泽。（我只是使用HP 58503A定时接收器来生成10 MHz频率参考 - 我个人不在乎设备上的时间是几十ns慢。但真正的时间坚果呢！）有人写道列表+“通常的方法是校准整个设置，包括天线，LNA，电缆和接收器。即你开车到国家实验室，设置你的整个系统，然后测量你的GPS接收器的时间差异实验室，开车回家，并应用校正。“+所以基本上回答你关于准确性的问题，答案就像使用VNA 一样准确。当然，如果你知道一个更合适的工具，请随意提及它，但你的专业知识显然是在VNA中，而且它是我想到的工具。显然，滤波器上的群延迟通常可能为15或65 ns。我有点不愿意将GPS天线从我的HP定时接收器上断开，因为我知道它会影响频率精度，因为它进入“保持”状态，并且它不能立即恢复。但也许我会设置8720D，偏置端口2耦合器，以便GPS接收器具有所需的5V，并尝试测量。 Dave.Edited：drkirkby于2015年2月17日下午1:23 以上来自于谷歌翻译以下为原文 Hi Joel, I only just noticed your reply, so please excuse the delay in replying. I don't actually want to make the measurement myself, but I see the question asked on the time-nuts mailing list. That list is read by people who go to great lengths to measure time and frequency very accurately. The person who set the list up has a wrist watch which keeps time to a few ns per day, although the battery life is only 45 minutes. http://leapsecond.com/pages/atomic-bill/ Tom, who runs that list, has some great stuff on his web site, including his chess set which should be appreciated by all RF engineers. He has taken several HP cesium clocks up a mountain for an experiment. I suspect 20% of the people reading time-nuts personally own at least one cesium frequency standard, and at least one has his own hydrogen maser. (I just make do with an HP 58503A timing receiver to generate a 10 MHz frequency reference - I don't personally care if the time on the unit is a few tens of ns slow. But true time-nuts do!) Someone wrote on that list +"The usual way is to calibrate the whole setup, including antenna, LNA, cable and receiver. Ie. you drive to the national lab, set up your whole system, then measure the timing difference of your GPS receiver to the one of the lab, drive back home, and apply the correction."+ So basically to answer your question about accuracy, the answer is as accurate as it is possible using a VNA. Of course, if you know of a more appropriate tool, feel free to mention it, but your expertise is obviously in VNAs, and it was the tool that came to my mind. Apparently group delays on the filters are likely to typically 15 or 65 ns. I'm a bit reluctant to disconnect the GPS antenna from my HP timing receiver, as I know it will impact the frequency accuracy, as it goes into "holdover", and it does not recover instantly. But maybe I will set up the 8720D, bias the port 2 coupler so the GPS receiver has the required 5V, and try the measurement. Dave. Edited by: drkirkby on Feb 17, 2015 1:23 PM

2018-11-1 12:02:39 评论举报李青