Reception

© 2010-2022, Kevan Hashemi Open Source Instruments Inc.

Contents

Introduction
Experiments
2010201120202021
2022

Introduction

[14-MAR-22] Here we record our work on measuring and improving reception of telemetry signals by our SCT data acquisition system. Before investing in one of our telemetry systems, check the cell phone tower database to see if there is a base station nearby. Radio frequency telemetry can be challenging if we are within fifty meters of the most powerful base stations, and within ten meters of the weaker ones.

Experiments

2010

[26-JUL-10] We receive M1278417564 from Rob at ION. Transmitters No4 and No8 record EEG for an hour. Rob is pleased with the recordings, but reception robustness is only 75% for both transmitters, while our target is 95%. We do not understand the poor reception. Earlier this year, Matthew fixed poor reception in one experiment by re-seating the enclosure lid. Rob suspects that the faraday enclosure lid was not replaced properly by the animal caretakers, but we cannot confirm this hypothesis.

[06-AUG-10] At CHB, we record 1000 seconds of data in archive M1281121460 from a rat roaming freely in the faraday enclosure with transmitter No10. We use a newly-refurbished Data Receiver (A3018C). The transmitter electrodes cemented to the skull using silver epoxy. The rat spends most of its time along the edges of the enclosure and in the corners, often pressing the transmitter close to the conducting walls. Reception in 4-s intervals is 93% on average, 5% minimum and 99% maximum.


Figure: Rat Roaming Freely in Faraday Enclosure. Archive M1281122799.

We put the rat in a cage within the enclosure. It roams around the cage, going from within a few centimeters of the antenna to within a couple of centimeters of the wall. We record 140 seconds in archive M1281122799. Reception is 98.3%, with minimum 97% and maximum 99.3%.

[10-AUG-10] At CHB, Yingpeng implants transmitter No8 and Sameer records three one-hour archives. Speaking of the first archive, he says, "I observed that the signal reception had dropped significantly when I was checking mail on my iphone while sitting close to the cage (File # M1281455686, t~800sec). So I deliberately turned on the 3G network on my phone and the EEG reception was lost again (File # M1281455686, t~1100)."

At times 800 s and 1100 s, reception from both transmitters stops almost completely and simultaneously. Also, Sameer injects both animals with kainic acid during the recording, which requires the lid of the faraday enclosure to be removed. Injection times are No8 300-365 s and No10 370-430 s. For the entire M1281455686 recording, reception robustness was 90% for No8 and 95% for No10. Our target is 95%.

We looked up the frequency and power output of the iPhone. In the US, it uses 869-894 MHz. The maximum permissable output power for a cell phone in this band is 33 dBm, or 2 W, and it appears that most phones are able to transmit the full 2 W, although they most often operated at much lower power output. Even with the best band-pass filters, there will still be 10% of the power spilling over into the low end of our 902-928 MHz ISM band. Our transmitters project around 50 μW out of the animal's body. The enclosure we lent to ION provides between 20 dB (99%) and 40 dB (99.99%) interference rejection, depending upon how well the lid is sitting on the frame. Furthermore, the signal from a transmitter must be at least 10 dB (ten times) more powerful than interference for proper reception. It is easy to see that an iPhone transmitting at the right frequency, just outside the enclosure, will stop reception from an implanted transmtter.

Furthermore, this setup uses an unshielded cable to deliver power to the Data Receiver. It turns out that unshielded cables are associated bad messages, which suggests that they allow interference to enter the system and corrupt the radio reception. See here for more details.

In M1281460570 we see three periods of simultaneous signal loss and one period several minutes of poor reception from transmitter No8. For the entire recording, robustness is 92% and 98% for No8 and No10 respectively.


Figure: Reception from Two Implanted Transmitters at CHB. Archive M1281464170.

In M1281464170 we see no periods of simultaneous signal loss, as you can see in the above graph. Robustness is 95% and 99% for No8 and No10 respectively.

[11-AUG-10] We hear from Stephanie at ION on the subject of cell phone interference. "How interesting! Rob certainly has an iphone, and while there was no computer up there, standard procedure involved using said iphone to call matthew in his office to ask if transmitters were on or off."

[12-AUG-10] Sameer sends us M1281643595 and M1281647588 in which the signal from implanted No6 is recorded over 7000 s. The following figure shows reception during all 4-s playback intervals.


Figure: Reception from Implanted No6 Transmitter. Archive M1281643595. Average reception is 97%. Robustness is also 97%.

There are three periods of poor reception. The first is at around 300 s, where reception drops to zero for a few intervals. Sameer says, "Also the iPhone interference (done on purpose to reconfirm the finding) can be seen in the period t~270 to 300sec in file M1281643595." The second period is from 3500 s to 4500 s, when reception occasionally drops below 80%. The worste period is around 6000 s, when reception is below 80% most of the time for around 100 s.

[18-AUG-10] Sameer recorded another six hours of data from No6, which has been re-implanted with screws in another animal. The data spans six hour-long archives. You will find a graph of reception versus time here. The first archive is M1281985381. Average reception is 98.3%. Robustness is 99.8%.

[25-AUG-10] Receive another six hours of data from Sameer at CHB, starting with archive M1282668620 and ending with M1282686620. The rat was less active and more asleep during these six hours. We plot reception here. Average reception is 97.6% and robustness is 97.6%. There are eight periods of poor reception, two of which see reception drop to zero. The first may be explained by the enclosure lid being improperly seated. We have no information about the cause of the other periods.

[23-SEP-10] We receive seven hours of recordings by Tsung and Yingpeng of CHB from two transmitters. Transmitter No1 is a new A3019A and No8 is an A3013A. Two hours are from 15-SEP and the remaining five from 16-SEP. We apply the TPSPBP processor to obtain characteristics and run the RA analysis in the Toolmaker to calculate reception and robustness. Transmitter No1 has average recption 94.5% and robustness 94.8%. Transmitter No8 has average reception 96.9% and robustness 98.3%. We see that the new, smaller transmitter perfroms slightly less well, but still satisfies our target of 95% robustness. Closer examination of the data shows that reception from No1 is weaker in the first hour, with robustness 89.7%, and stronger in the other six hours, with robustness 95.7%.

[24-SEP-10] We apply the RF analysis to the same characteristics files to look for reception failure. The analysis generates a list of events. Each event is reception dropping below 20%. We obtain 31 such events in all, of which are on No1, the A3019A. The two longest periods of reception failure are "M1284662749.ndf 768 1 22" and "M1284662749.ndf 860 1 6". The first one was loss of reception for a full 88 seconds. At the same time, No8 reception was robust.

[18-NOV-10] Today we discovered the importance of shielded cable for the connection between the Data Receiver and the LWDAQ Driver. An unshielded cable picks up interference and greatly aggravates the system. We switched to a shielded LWDAQ cable and performed tests upon this system. We have transmitter No7 in the lower enclosure, close to the antenna, so we are certain of a strong signal. We start with an A3015A with a 3-dB attenuator and record the number of messages in channel No7 each second, as well as the number of bad messages per second. After 200 s we remove the attenuator and record for another 200 s.


Figure: Effect of Attenuator. We remove the 3-dB attenuator in the antenna at time 200 s. Accepted messages in channel No7 are plotted on the left axis. We expect 512 per second with no interference. Bad messages, which are those received in other channels when no such transmitters are active, are plotted on the right axis.

In the graph we see interference coming and going as some external source of 915-MHz power turns on and off. Interference generates bad messages. When we remove the attenuator, we see ten times as many bad messages during interference, and ten times as many such messages being accepted into the transmitter data.

The following series of tests explore the effect of attenuators, terminators, and interference. We start with the system shown here, with 3-dB antenna attenuators. In each case, we calculate reception by taking the average of ten one-second intervals. When we show the number of bad messages, we wait until the bad message rate jumps up and record at that time.

TestConfigurationReception
1No7 in FE2A near antenna99.3%
2Disconnect FE2B97.1%
3Terminate open socket99.3%
4Remove 3-dB antenna attenuator100%
5Restore 3-dB and rotate antenna loop97.2%
6Move transmitter99.7%
7Remove terminator99.6%
8Reconnect FE2B99.7%
9Remove 2 terminators on unused combiner sockets94.9%
10Restore 1st terminator99.3%
11Restore 2nd terminator99.9%
12Remove 1st terminator99.5%
13Remove 2nd terminator94.4%
14Restore 2 terminators99.9%
15Remove 2 terminators and 3-dB antenna attenuator99.8%
16Move No7 to FE2B99.9%
17Restore 2 terminators99.9%
18Remove 3-dB atenna attenuator99.9%
19Move transmitter until reception is weak76.6%
20Put 3-dB attenuator at cage wall0%
21Remove combiner and connect directly to data receiver99.7%
22Remove 3-dB attenuator99.4%
23Restore 3-dB attenuator to cage wall99.2%
24Remove 3-dB attenuator, restore combiner67%
25Replace combiner with 6-dB attenuator68%
26Restore combiner, unshielded root cable42%
27Add 3-dB attenuator to antenna, unshielded root cable0%
28Remove combiner, unshielded root cable15%
29Remove 3-dB attenuator, unshielded root cable90%
30Move transmitter close to antenna, unshielded root cable88% + 500 Bad/s
31Add 3-dB attenuator to antenna, unshielded root cable97% + 40 Bad/s
32Remove 3-dB attenuator, unshielded root cable90% + 800 Bad/s
33Restore shielded root cable100% + 100 Bad/s
34Add 3-dB to antenna99.7% + 5 Bad/s
Table: Effect of Attenuators, Shielded Data Cable, and Other Factors. The transmitter is No7. The root cable is the cable from the data receiver to the LWDAQ driver.

Tests 1 to 18 show that when our signal is strong, unused combiner sockets should be terminated. In one case we see reception drop from 99% to 94% because of poor termination. In tests 19 to 25, the transmitter signal is barely strong enough for detection by an antenna without an attenuator. Adding any form of attenuation in the antenna cable causes reception to drop. The combiner affects the signal like a 6-dB attenuator.

In tests 26 to 29, we have a weak signal and an unshielded root cable. Between 24 and 26 the only change is removing the root cable shield. Reception drops from 67% to 42%, which may or may not be significant. But we see no dramatic increase in the bad message rate when our transmitter signal is weak and we remove the root cable shield. With no attenuator and no combiner, we get 90% reception.

In tests 30 to 34 we move the transmitter close to the antenna so that we have a strong signal. We start recording the bad message frequency. The source of these bad messages is suppressed both by the 3-dB attenuator and the shielded cable, and most of all by both acting together.

We conclude that a 3-dB attenuator in the antenna will improve reception when the transmitter signal is strong. When the transmitter signal is almost too weak to receive, the additional attenuator will degrade reception. We plan to overcome the degradation caused by the 3-dB attenuator in the future with the help of an active antenna combiner: the A3021.

The above experiments are closely related to our experiment with shielded and unshielded LWDAQ cables in the presence of a 3-dB antenna attenuator. A shielded cable decreases the bad message by a factor of ten. From the above experiments we see that a 3-dB attenuator on the antenna also decreases the bad message rate by factor of ten. When we remove the attenuator and the shield, the bad message rate increases by a factor of a hundred.

[19-NOV-10] Today we measured reception with random movement on the end of a stick within our FE2A enclosure. Our objective was to determine how the 3-dB attenuator affects reception and to better understand the source of bad messages in the OSI office. We have two transmitters: an A3013A without encapsulation, No7, and an A3019A with encapsulation, No1. We move and rotate the transmitter inside the cage for a minute and calculate the average reception, the robustness, and bad message rate.

TestConfigurationReceptionRobustnessBad Rate
35A3013A, 0-dB antenna, no combiner93%90%<1/s
36A3013A, 3-dB antenna, no combiner93%89%<1/s
37A3013A, 3-dB attenna, combiner84%74%<1/s
38A3013A, 3-dB attenna, combiner, FE2B added87%70%<1/s
39A3019A, 3-dB attenna, combiner, FE2B added78%53%<1/s
40A3019A, 0-dB antenna, no combiner92%82%<1/s
41A3019A, 3-dB antenna, no combiner94%92%<1/s
42A3019A, Turn absorber grey side up88%92%<1/s
43A3019A, Absorber black side up,
put absorber fragments in receiver box
94%93%<1/s
44A3019A, Repeat84%78%108/s
45A3019A, Repeat91%80%234/s
46Remove absorber from receiver. Turn off transmitter.0%0%500/s
47Disconnect FE2A0%0%0/s
48Restore FE2A, 6-dB attenuator at receiver box,
3-dB at antenna
0%0%0/s
49Remove 6-dB attenuator0%0%400/s
50Remove antenna leaving 3-dB attenuator0%0%0/s
51Remove 3-dB attenuator0%0%0/s
52Restore antenna0%0%100/s
533-dB at antenna enclosure0%0%0/s
54Remove 3-dB from antenna enclosure0%0%10/s
Table: Reception and Bad Message Rate Under Various Conditions. Note that the bad message rate varies with time, regardless of the configuration. We see no bad messages until test 44. The transmitter is always in the FE2A enclosure, which has a hole in it through which we can run a stick to move and rotate the transmitter in the enclosure volume. The LWDAQ cable is shielded and only 1-m long.

We see the bad message rate going up and down as we watch without altering the system. We try to wait until we see the rate go up before we make our measurement. Today we see high bad message rates even when the transmitter is off. The bad messages stop when we disconnect the antenna. They stop if we put 9 dB of attenuation between the antenna and the receiver, but not when we insert only 3 dB. Our observations are consistent with powerful interference entering the faraday enclosure and resonating between its walls. The poor performance of the FE2A is evident in our earlier experiments. The FE2A absorber is half as thick as the ones we settled upon for the FE2B, and is on the floor instead of glued under the lid.

[31-DEC-10] We left two transmitters running in two faraday enclosures for three hundred hours. Antennas are A3015Bs with 3-dB attenuators installed. Instead of an antenna combiner, we use a BNC T-junction at the Data Receiver. We obtain the following reception, averaged over each hour with the help Interval Analysis.


Figure: Reception with T-Junction Combiner and Two A3015B Antennas. Transmitter No7 is in the FE2A enclosure, No9 is in the FE2B.

We also use analysis to search for periods when reception drops below 90%, and find that this occurs during only one twenty-second period during the three hundred hours. During this twenty-second period, reception drops to zero for both transmitters.

[10-JAN-11] We incorporate an Antenna Combiner (A3021B) into our system. This combiner has amplification before combination. We plug the antennas into the combiner. We do not terminate the unused combiner inputs. We obtain the following reception. We note that No9 has not moved since the T-Junction experiment.


Figure: Reception with A3021B Combiner and Two A3015B Antennas. Transmitter No7 is in the FE2A enclosure, No9 is in the FE2B.

We see that reception is substantially improved with the introduction of the active antenna combiners. We searched for periods of poor reception and found two. We examined the raw data in the Neuroplayer and found that both eight-second periods of poor reception contain thousands of bad messages.


Figure: One of Two Reception Failures During 100 Hours. Transmitter No7 is in the FE2A enclosure, No9 is in the FE2B. For the other failure, see here.

We see that the antenna attenuator, the active antenna combiner, and the shielded root cable together reduce the frequency of these bad-message failures from once every few minutes to once every few days.

2011

[27-JAN-11] Joost at ION sets up a four-enclosure system with our new A3015B antennas and our new A3021B antenna combiner. One of his antenna cables is ten meters long. He places twelve transmitters in his cages. He says, "I tested all transmitters in the setup you suggested. I have attached two characteristics files. The first with all transmitters close to the antennae and the second with the transmitters in the corners of the enclosures. Transmitter 9 is implanted, the rest is not."


Figure: Reception from Twelve Transmitters from Four-Enclosure System with Active Antenna Combiner. Transmitter No9 is implanted. For first hour, other eleven are close to antenna. For second hour, they are in enclosure corners. Archives M1296139069 and M1296142669.

Average reception is greater than 90% for all twelve. According to our simulations, collisions alone will lower the average reception from twelve transmitters to 92%, with an occasional minimum of 52% and average robustness of 97%. Robustness for the twelve transmitters over two hours, as measured in four-second intervals, is as follows: No1 100.0%, No2 99.9, No3 99.9%, No4 98.9%, No6 99.7%, No7 99.9%, No8 99.3%, No9 95.2%, No10 99.9%, No11 95.4%, No12 96.5%, No13 96.8%. In short: reception is superb. Our target is 95% robustness with 8 transmitters.

[22-FEB-11] Rob at ION sends us recordings in M1298209850 from three implanted transmitters in a four-cage system. Reception is 98% or higher for all three transmitters. We see occasional reception drops in reception, and these tend to affect to transmitters at a time.


Figure: Reception from Three Implanted Transmitters.

The coincidence of reception drops suggests external interference is causing the drops, but we see no bad messages in the data during the drops.

[14-MAR-11] While at CHB, we noticed reception failure from an implanted transmitter. We lifted the lid of the faraday enclosure. Reception returned to near 100%. We replaced the lid, reception dropped to near zero. We touched the mesh walls. Reception recovered. We opened the cage and moved the antenna 10 mm. Reception was robust again. The animal was near a metallic wall of the cage, with the antenna on the far side of the wall. We rotated the cage so that the antenna would never have metal in the line of sight transmission. We did not observe drop-out again that day.

[03-APR-11] We receive from Joost 15 hours of recordings from control animals at ION. The recordings were made on 13-FEB-11 with four faraday enclosures, eight animal cages, an A3021B active antenna combiner, and an A3018C data receiver. The following graph shows minute-by-minute reception during the entire 15 hours.


Figure: Reception from Eight Implanted Transmitters.

Average reception ranges from 94.4% to 95.7%. We expect a loss of 5% from collisions, so we are well-satisfied with the system's performance. There is one period of a minut on No11 when reception drops almost to zero. Other than that, a more detailed search through the data shows hourly drops below 20% reception lasting around ten seconds.

[28-JUN-11] We repaired and returned Louise's A3018C Data Receiver, and she tried it out again in her laboratory with three transmitters and no faraday enclosure. Here is reception for an hour. We see periodic collisions between pairs of transmitters. At time ≈200 s we see reception from all three transmitters dropping from external interference. Maximum reception is 100% and minimum is 77%.


Figure: Reception in Louise's Laboratory, Three Transmitters, No Faraday Enclosure. The X signal from all three transmitters shows 50 Hz mains hum of amplitude 4 mV and similar amplitude harmonics at 100 Hz and 150 Hz.

Louise and Lukasz took the Data Receiver down to their animal building and recorded from the same three transmitters on plastic cups in a faraday enclosure. Here is reception for one hour. We see the periodic collisions between pairs of transmitters that we expect. Minimum reception of around 86% occurs when all three transmitters collide at the same time. Maximum reception, however, is only 98%.


Figure: Reception in Louise's Animal Building, Three Transmitters in Faraday Enclosure. The X signal from all three transmitters contain a peak at 90.5 Hz of around 20 μV, but no peak at 50 Hz.

We examined the signal at time 500 s, when collisions are at a minimum. Roughly 2% of the messages are missing. The missing messages are distributed at random. There are no bad messages.

2020

[21-JAN-20] We receive 144 hours of EEG from Cornell recorded by A3028P1-AA in a mouse. Random checks of reception during the 144 hours show 100.0%. Analysis of first hour in one-second intervals gives average reception 99.998%.

[12-FEB-20] We receive EEG recordings from Taiwan of two transmitters in a locally-made Faraday Enclosure, see here. One transmitter, No19, acts as a reference in the left-hand cage. The other transmitter, No9, is an A3028E-AA implanted in a rat in the right-hand cage. We have recordings from three arrangements of the two antennas in the enclosure.


Figure: Reception with Antennas Against Left and Right Walls of Locally-Made Faraday Enclosures in Taiwan.

In the plot above, reception drops as the animal moves away from the nearby right-wall antenna. We now have one antenna in the center of the enclosure, between the two cages, and one near the right wall, so that the two antennas are on either side of the cage containing the animal.


Figure: Reception with One Antenna Centered and One Against Right Wall of Locally-Made Faraday Enclosures in Taiwan.

With the two antennas centered, we obtain the following reception over a three-day period.


Figure: Reception with Both Antennas Centered in Locally-Made Faraday Enclosures in Taiwan.

Reception is poor unless we have an antenna on either side of the animal cage, in which case it is excellent.

2021

[24-JUN-21] We receive five hours of recordings from UCB Pharma, where they have three A3028P1-AA-C37-C transmitters implanted in mice in a set of four FE3A enclosures. Each FE3A is equipped with four Wisenet X-Series XND-6080 video cameras and four A3015C loop antennas connected to an Octal Data Receiver. Each antenna shares a data receiver input with another antenna in another FEW3A by means of a BNC T-Adaptor. During the first three hours, their video cameras on the back walls of the enclosures are powered up, running, and not covered with steel mesh, while the cameras on the ceiling are covered with mesh. During the final two hours, the back wall cameras have been disconnected from power.


Figure: Reception with Four Antennas in FE3A with and without Camera Interference. Archives are M1624519237.ndf, M1624522837.ndf, M1624526437.ndf, M1624527768.ndf, M1624531368.ndf.

To obtain the above plot, we processed 8-s intervals with a processor script consisting of only one line:

append result "$info(channel_num) [format %.2f [expr 100.0 - $info(loss)]] "

We applied our reception averaging interval analysis to the characteristics files generated by the above processor, and so obtained the average reception per minute for the entire 120-minute recording. The camera interference stops at time 2.4 hr. From that time onwards, reception for the three channels is 99.6%, 99.9%, and 99.7%. Our customers at UCB Pharma tell us that the disruption of reception by the cameras on the ceiling before they were covered with mesh was even greater. The ceiling cameras are equipped with infrared lamp arrays. We hypothesize that it is the camera power supplies that are generating microwave noise that interferes with reception of SCT signals.

[08-SEP-21] We have three hours of recordings from UCB from each of two recording systems. Each recording system consists of four FE3AS enclosures, sixteen antennas, and one Octal Data Receiver. There are 47 transmitter in all, we process all six hours and write reception to disk. Median reception is 99%, mean is 98%. We count the number of 8-s intervals in which reception is less than 80% for all channels using code below.

set fnl [LWDAQ_get_file_name 1]
set histogram [list]
foreach fn $fnl {
	set f [open $fn r]
	set contents [split [string trim [read $f]] \n]
	close $f

	foreach interval $contents {
		foreach channel [lrange $interval 2 end] {
			set index [lsearch -index 0 $histogram $channel]
			if {$index >= 0} {
				set count [expr [lindex $histogram $index 1] + 1]
				set histogram [lreplace $histogram $index $index "$channel $count"]
			} else {
				lappend histogram "$channel 1"
			}
		}
	}
}

LWDAQ_print $t "Found loss in [llength $histogram] channels."

set histogram [lsort -increasing -index 0 $histogram]
foreach record $histogram {
	LWDAQ_print $t $record
}

There are 22 channels of 47 with loss in at least one interval. Two have loss more than 10% of the time: No185 at 15%, No187 at 18%. During loss periods, reception is almost always greater than 60%.

[12-NOV-21] We have four hours of recording from each of four Animal Location Trackers (A3038B) each with one animal with an SCT, and three with another animal without an SCT. We have continuous top-down video from all three cages. We plot reception below.


Figure: Reception from One SCT on Each of Four ALT (A3038B). No88, No109, and No113 are A3038P1 at 128 SPS with the 13-mm helical C-Antenna. No75 is A3038S2 at 256 SPS with 30-mm thin loop D-Antenna. Average reception is No75 96.5%, No88 92.0, No109 97.3%, No113 99.5%.

Reception from the C-Antenna is adequate. Reception from the D-Antenna is almost perfect except for a ten-minute period when it drops to 25%. The ALTs provide average background power measurements for the 900-930 MHz band. Average background power is 57 counts, which for the A3038DM-C detector modules of the A3038B is around −63 dBm. During the ten-minute loss, the animal No75 is completely still. Two detectors receive power 98 counts, or −50 dBm, which should be adequate for reception, it being 13 dB above background. When we visited UCB in November 2019, we found it was interference generated by their cameras that was disrupting reception with their Octal Data Receiver. There are four cameras in each Faraday enclosure. But when we measured 850-1000 MHz interference in the enclosures with our spectrometer (A3008), we found none. We were able to improve reception dramatially by covering all cameras with stainless steel mesh. The UCB engineer later observed that it was the cameras providing illumination that caused the greatest disruption, and suggested that it was the lighting power supply that was generating the noise. We agree with this suggestion. The cameras are power over ethernet (PoE), so contain 48-V converters. These can produce powerfule 100-ns electromagnetic pulses that would not be detected by our ALT power measurement or our spectrometer, and yet would distrupt one or more bits of an incoming SCT message. If so, the loss would be random rather than complete, and ALT activity measurement through SCT power reception would remain accurate even when we are receiving only 15% of the messages. We find this is indeed the case: the ALT sees the animal as stationary.

[06-DEC-21] We install eight antennas into an FE5A Faraday Canopy, feeding the cables into the enclosure through an 8-to-4 Coaxial Feedthrough (A3039C). The feedthrough combines eight interior antenna signals into four exterior signals.

Number
of Antennas
Reception
02%
1 (unpaired)75%
2 (unpaired)85%
3 (unpaired)97%
4 (unpaired)99%
5 (paired with 1)100%
6 (paired with 2)100%
7 (paired with 3)100%
8 (paired with 4)100%
Table: Average Reception Throughout a Faraday Canopy (FE5A) versus Number of Antennas (Nathan Sayer). We use an 8-to-4 Coaxial Feedthrough (A3039C) to bring antenna signals out of the enclosure.

The antennas are arranged on the face of the absorbers on the left and right wall of the canopy.

2022

[13-MAR-22] We receiver three hours of recording from four A3028C transmitters implanted in mice in an IVC rack within an inner room at University of Manchester, see here. The building is brick, and we assume the walls of this inner room, which has no windows, are likewise made of brick. The door is a fire door, which we assume is made of metal. There is no Faraday enclosure around the rack, and yet we obtain near-perfect reception, average 99.4% and higher.


Figure: Reception from Four SCTS over Three Non-Consecutive Hours. No Faraday enclosure, brick-walled inner room in Manchester.

[15-MAR-22] We receive recordings from Marsaille, where we have an ALT in an FE3A enclosure, and reception is around 50%. Upon obtaining latitude and longitude of their recording room, on the top floor of their building, we consult the Open Cell ID database and find two nearby mobile phone base stations, one immediately on top of their room, and another some fifty meters away.


Figure: Mobile Phone Base Stations Near Campus Sainte Timone. For an annotated satellite view of the roof see here. The L tower is LTE (4G base station) and the G is GSM (2 G base station).

According to GSMArena, the mobile phone networks in France are as follows. We have GSM for "global system for mobile", UMTS for "Universal Mobile Telecommunications Service", LTE for "long term evolution", and 5G for "5G". The numbers in parenthesis are band numbers, which we can use to look up the exact frequency ranges.

2G: GSM 900, GSM 1800
3G: UMTS 900, UMTS 2100
4G: LTE 700 (28), LTE 800 (20), LTE 1800 (3), LTE 2100 (1), LTE 2600 (7)
5G: 5G 2100 (1), 5G 3500 (78)

The L tower was last measured by the mapping agency in 2015. It is right on top of the animal laboratory. The G tower was last measured in 2021. It is seventy meters from the laboratory. Our telemetry system uses 900-930 MHZ. The LTE 800-MHz band is 832-862 MHz. The GSM 900-MHz band is 880-915 MHz. Both use 1800 MHz, LTE in the range 1850-1910 MHz, and GSM in the range 1805-1880 MHz. The GSM transmitter appears to be facing away from the laboratory. At range 70 m, assuming 1 kW power, if it radiated in all directions equally, its power would be 16 mW/m2. Base station antennas typically focus 30% of their power into their narrow beam, so we are left with 5 mW/m2 in the laboratory. Our FE3A enclosure provides at least 25 dB isolation for 900-930 MHz, dropping the power in the enclosure to around 15 μW/m2. On of our ALT antennas, with a 3-cm diameter for collection, will pick up no more than 15 nW, or −48 dBm. Our telemetry should function adequately with this as a maximum interference power. The LTE station at 1800 MHz is no more than 10 m away. The isolation of the FE3A we assume is similar to that of our FE2F, which we measured here. At 1800 MHz the isolation is around 15 dB. Assuming the laboratory is out of the beam of the LTE transmitter, we arrive at 500 times as much power at our antenna, or −20 dBm. We find that the A3038DM-C detector module is vulnerable to 1800-1860 MHz. The DM-C can detect a −43 dBm SCT signal with at most −20 dBm of 1825 MHz. At 1875 MHz, it can tolerate +7 dBm. By ALT standards, −43 dBm a typical maximum coil power from an implanted tranmitter. If the animal moves off the platform, a maximum of −53 dBm is possible, in which case we would lose reception. With an additional 900-930 MHz filter to the antenna cable, however, our tolerance for interference increases to +10 dBm for 1800-1900 MHz.

[21-MAR-22] At Marsaille, our collaborators try a Damped Loop Antenna (A3015C) plugged into the auxilliary antenna input of their two A3038C ALTs.


Figure: Reception by A3038C with Damped Loop Antenna (A3015C) on Auxilliary Input. Left: P0158 with three A3028D dual-channel transmitters. Right: P0159 with two A3028D dual-channel transmitters.

We insert into the antenna cable a 902-928 MHz band-pass filter, CBPFS-0915, as shown here, making a Filtering Loop Antenna. We record for one hour from both ALTs.


Figure: Reception by A3038C with Filtering Loop Antenna (A3015C) on Auxilliary Input. Left: P0158 with 3 A3028D dual-channel transmitters. Right: P0159 with two A3028D dual-channel transmitters.

The table below gives average reception from each of the ten available channels with and without the filter.


Figure: Reception versus Channel Number and Antenna Type.

If we ignore transmitter 21/22, the average reception is around 98%.

[27-APR-22] We receive two hours of recording from A3028S2-AA-C50-C transmitters implanted in mice at UCB, recorded from A3038B/C animal location trackers (not sure if it's a B or C version). There are three mice over each ALT. These transmitters are equipped with the 13-mm helical C-Antenna.


Figure: Reception from Six A3028S2 with C-Antenna

Reception from transmitters 36, 37, and 39 exhibit a rare alignment of their transmit clocks. All three transmitters collide for half an hour. We see cyclic loss of reception as a result of the collisions. For an explanation of how these cyclic losses arise, see Collisions.


Figure: Reception from Six A3028S2 with C-Antenna

In order for three transmitters to collide, all three of their signals must arrive at the receiving antenna. In the case of the ALT, there are many receiving antennas. If the mice are separated, their signals will be received by a different set of antennas, and collisions are unlikely. Only when the mice are close together will their transmissions be received by the same set of antennas with similar strength. We examine the location tracking and find that during this half-hour, the three mice are indeed close together, moving occasionally, but mostly stationary.

[22-JUN-22] We compare the performance of various combinations of antennas in an FE5A Faraday canopy. We have a total of eight A3015C loop antennas, four on the left bank of absorbers and four on the right bank of absorbers. We move a transmitter around the entire volume of the enclosure and measure average reception for each configuration. When we combine antenna, we do so with an 8-to-4 Coaxial Combiner (A3039C).

Number
of
Antennas
Antenna ConfigurationReception
1One Independent83.2%
2One Combined Pair81.1%
2Two Independent96.1%
3Three Independent99.0%
4Two Combined Pairs84.7%
4Four Independent98.3%
6Three Combined Pairs99.7%
6Six Independent100.0%
8Four Combined Pairs100.0%
8Eight Independent99.9%
Table: Reception from Increasing Numbers of Antennas, Including Effect of Combiner. (Measurements by Nathan Sayer.)

[11-JUL-22] At UCB, we have four A3028S2-AA-C50-D transmitters implanted in mice. Two are in one cage over one ALT. Two are in another cage over another ALT. Both cages are in the same FE3A Faraday enclosure. We receive two hours of recording from each ALT. These transmitters are equipped with the new 30-mm thin loop D-Antenna. Average reception from the four transmitters in the four separate archives is as follows.

Archive         No86    No88    No91    No92
M1657184483.ndf 93.0    87.0    99.1    99.5
M1657184534.ndf 99.4    99.8    81.4    86.2
M1657188084.ndf 95.9    85.3    99.3    99.3
M1657188135.ndf 99.7    99.8    84.7    82.8

Our collaborators at UCB confirm that No86 and No88 are over one ALT while No91 and No92 are over another. Reception from the D-Antenna over an ALT is >99%. Reception from mice over a neighboring ALT is >80%.

[04-AUG-22] We receive a screen shot of signals recorded from a rat at Marsailled using the modified A3038D with no auxilliary antenna attached. Reception is around 90%, with loss in chunks of up to thirty seconds at a time, see here. Our best guess is that there is 900-MHz interference in addition to 1840 MHz from the base station on their roof.

[14-SEP-22] We have recording M1647868967.ndf made at Marsaille on 21-MAR-22. The data receiver is ALT P0159, version A3038C. It is equipped with a damped auxiliary antenna (A3015C). The auxiliary antenna has no coaxial bandpass filter. We compare background power, signal power, and reception. The background power is available in the channel No0 signal. We use the maximum background power seen in the fifteen detector coils as our measurement of background power. We ignore the power in the auxiliary antenna. We obtain the maximum signal power from the same fifteen detector coils. We use SCT channel No13 implanted in a rat for our signal power and reception measurements.


Figure: Marsaille Reception, Signal Power, and Background Power in A3038C P0159 with Damped Auxiliary Antenna. Power in ADC counts, 30 counts is 10 dB, M1647868967.ndf.

Here we are seeing background up to 140 cnt, far higher than the 80-count background we see in our own enclosures. It is this powerful and variable background power that motivates us to design the A3038D, where each detector coil has a 902-938 MHz bandpass filter in its short detector cable.

Today, in the OSI Faraday canopy, we record from P0150, an A3038C, with no auxiliary antenna. We have five transmitters on a pendulum swinging 50 cm above the platform. We agitate the pendulum every few minutes to keep the transmitters moving. We keep the canopy sealed until 1600 s, then open it from 1600-1800 s. We concentrate on No20. All transmitters are in air.


Figure: Waltham Reception, Signal Power, and Background Power in A3038C P0150 with No Auxiliary Antenna. Power in ADC counts, 30 counts is 10 dB, M1663169974.ndf.

We have recording M1659126880.ndf from Marsaille, 29-JUL-22, from P0159, now A3038D enhanced with coaxial filters in series with all detector coils. No auxiliary antenna. We follow transmitter channel No25 implanted in a rat. Compared to March, background power is low and stable. But signal power varies greatly.


Figure: Marsaille Reception, Signal Power, and Background Power in A3038D P0159 with No Auxiliary Antenna. Power in ADC counts, 30 counts is 10 dB, M1659126880.ndf.

We perform the same measurement for channel No25 in M1661115196.ndf recorded on 21-AUG-22 with P0160 A3038C equipped with filtering auxiliary antenna (902-928 MHz bandpass filter in auxiliary antenna cable). The No25 SCT is implanted in a rat. We see background power is low and stable in P0160, even though it has no filters on its detetor coil cables.


Figure: Marsaille Reception, Signal Power, and Background Power in A3038C with Filtering Auxiliary Antenna. Power in ADC counts, 30 counts is 10 dB, M1661115196.ndf.

Here is the same measurements obtained from M1657188084.ndf recorded on M1657188084.ndf from an A3038C. We use SCT No91, implanted in a mouse, for our reception and signal power.


Figure: Brussels Reception, Signal Power, and Background Power in A3038C with No Auxiliary Antenna. Power in ADC counts, 30 counts is 10 dB, M1657188084.ndf.