Antenna cable length

Q&A forumCategory: QuestionsAntenna cable length
13vadimka13 asked 2 weeks ago

Hello, everyone! Happy new year! My receiver: Starter Kit Simplertk2b v1.1. I want to short antenna cable from standart 5 m to 10 cm. My aims: land survey in RTK, PPK, PPP, static mode and accuracy 10 cm regarding ground control marks. Reason of shorting: antanna and board in one case, near 3 cm between its. Is it real? If yes, what minimal length it must be? What features in U-center I must change to adjust receiver for my accuracy aims? At this time, cable is surounding the board.

clive1 replied 2 weeks ago

I wouldn’t hack up an ANN-MB, find an L1/L2 with a TNC connector, and get a short pig-tail SMA-to-TNC. A Right-Angle SMA would fit into tighter spaces.

Something equivalent to:
https://www.amazon.com/pigtail-wireless-router-Quality-Shipping/dp/B01CWJ4SSQ

You don’t need to adjust the receiver, it is measuring the signal as it arrives at the phase-center of the antenna. The cable length skews time a little, not the position. For short cables don’t have super-high gain antennas (ie look for 10-20 dB rather than 30-40 dB)

13vadimka13 replied 2 weeks ago

Clive1, Hello! Thank you for answer! In this U-blox manual for ANN-MB: https://www.u-blox.com/sites/default/files/products/documents/GNSS-Antennas_AppNote_%28UBX-15030289%29.pdf write that “The use of an active antenna is always advisable if the RF cable length between the receiver and
antenna exceeds about 10 cm. Care should be taken that the gain of the LNA inside the antenna does
not lead to an overload condition at the receiver. For receivers that also work with passive antennas
an antenna LNA gain of 15 dB is usually sufficient, even for cable lengths up to 5 m. There is no need
for the antenna LNA gain to exceed 26 dB for use with u-blox receivers (at the RF input). With shorter
cables and a gain above 35 dB, an overload condition might occur on some receivers.” As I understand it, I can shorten it to 10 cm. If there is an overload, will the receiver be damaged? If there’s a protection from overloading the signal?

13vadimka13 replied 2 weeks ago

I won’t hack up ANN-MB, because I may to cut cable and establish new SMA.

1 Answers
13vadimka13 answered 2 weeks ago

I shortened the cable to 20 cm ANN MB antenna. Nothing has changed, everything is working well