TCXO upgrade

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N4XTL
 

Posts: 19
Joined: 08 Jul 2022, 01:44

TCXO upgrade

Post by N4XTL »

Hi,

I am very new to the (tr)uSDX but already looking for ways to modify and tinker with mine. One upgrade I identified right off the bat is a TCXO upgrade. I know that the PCB is not set up to support one, but perhaps it can be bodged in.

One thing I discovered while exploring this possibility is that the PLL chip on my board is not a genuine Si5351, but a MS5351M. This article suggests that it performs well and is a suitable substitute, but it was an interesting discovery. It shouldn't have any impact on a TCXO mod.

I designed a small PCB (15mm x 10mm) that I plan to test for a TCXO mod. My thought is to remove the 27 MHz crystal and then use two of its four pads for the clock signal input (to Xa on the MS5351M) and ground. VDD for the TCXO will be connected at the cathode of D2 where the 3.3V supply for the PLL chip is generated. That diode pin and the two necessary pads from the crystal footprint are all in line on the main board. My small PCB has castellated vias that will be placed next to / above those pads. Connection will be made with a tiny bodge wire or perhaps just a blob of solder, depending on how things line up. The mod PCB will be glued to the top of two larger, nearby ICs for support. I don't like that very much, but there's really no where to secure the board otherwise.

tcxoupgrade918811.png
tcxoupgrade918811.png (5.35 KiB) Viewed 883 times

The TCXO I picked is a 27 MHz +/-500ppb part from Digikey that costs about $3 USD. The entire assembled mod PCB would cost perhaps $4 USD in parts, ignoring shipping and such.

If my idea works out I will update. It probably won't in its initial form but tinkering is the fun part! Any input is welcome.

Thank you.

Dan Watson
N4XTL
DL2RMM
 

Posts: 15
Joined: 07 Jan 2022, 21:15

Re: TCXO upgrade

Post by DL2RMM »

Hello Dan,

the mod sounds interesting. I'm suffering from frequency drift and would like to upgrade to TCXO as well.
My Hi-band version of the (tr)uSDX is using the FDT86256 as final MOSFET (Q5). The FDT86256 is located on the backside of the RF-board (compared to the 3x BS170s) and is directly facing the 27Mhz crystal.
Even with good efficiency (75%-82% on the 5 upper bands), the heat radiated by the MOSFET results in a frequency shift most pronounced when running FT8.
As a containment I experimented with a heat shield between RF- and main board and also tested a small fan. At the moment I run FT8 with the sidewall housings removed to get better heat removal and frequency stability.
See pic: https://www.qrz.com/db/K2RMM
So, a TCXO solution would be appreciated, please keep us updated.

73 de Jens DL2RMM (K2RMM)
DL2MAN
 

Posts: 418
Joined: 30 Dec 2021, 19:18
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Re: TCXO upgrade

Post by DL2MAN »

DL2RMM wrote: 09 Jul 2022, 09:50 (...) I'm suffering from frequency drift (...)
Hi Jens,

could you please be more specific about the frequency drift ?
When does it show ? Under what conditions ? I never experienced it myself, that´s why I´m asking.
Not even when TXing in WSPR mode for 2 minutes straight.

73 Mnauel; DL2MAN
DL2RMM
 

Posts: 15
Joined: 07 Jan 2022, 21:15

Re: TCXO upgrade

Post by DL2RMM »

Hi Manuel,

the drift only occurs when I transmit. When just receiving there is no drift at all.
Attached is an example of FT8 on 10meters today. When I start the 15sec transmitting cycles the waterfall shifts to the right. About 50Hz in 3minutes.
As mentioned before, I run the FDT86256 as Q5 on the backside of the RF-board. It is in close proximity to the 27Mhz crystal. Efficiency on 10m is close to 80%. The picture was taken when operating with the side walls removed. When adding my improvised "heat shield" between RF- and mainboard, the drift is cut in half. I did not recognize such a strong drift when I operated the Lo-band RF-board with BS170's.

73 de Jens, DL2RMM
drift when transmitting FT8 example 50Hz in 3minutes.jpg
drift when transmitting FT8 example 50Hz in 3minutes.jpg (192.6 KiB) Viewed 727 times
DL2MAN
 

Posts: 418
Joined: 30 Dec 2021, 19:18
Contact:

Re: TCXO upgrade

Post by DL2MAN »

Hi Jens,

thanks for the Hint. I actually never checked it with FDT86256, in deed.
Always with BS170´s.
Will check that..... Yes, there´s still bugs to be discovered ;)

73 Manuel; DL2MAN
Ohwenzelph
 

Posts: 105
Joined: 01 Jan 2022, 03:47

Re: TCXO upgrade

Post by Ohwenzelph »

Do you have an OSH Park file for the board? And what are you going to use for C1andC2?

Also, the the processor seems to connect to two sides of the crystal with two lines but the oscillator only has one "out" point, so how do you hook it up?
DL2MAN
 

Posts: 418
Joined: 30 Dec 2021, 19:18
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Re: TCXO upgrade

Post by DL2MAN »

DL2RMM wrote: 11 Jul 2022, 17:48 Hi Manuel,

the drift only occurs when I transmit. When just receiving there is no drift at all.
Attached is an example of FT8 on 10meters today. When I start the 15sec transmitting cycles the waterfall shifts to the right. About 50Hz in 3minutes.
As mentioned before, I run the FDT86256 as Q5 on the backside of the RF-board. It is in close proximity to the 27Mhz crystal. Efficiency on 10m is close to 80%. The picture was taken when operating with the side walls removed. When adding my improvised "heat shield" between RF- and mainboard, the drift is cut in half. I did not recognize such a strong drift when I operated the Lo-band RF-board with BS170's.

73 de Jens, DL2RMM
drift when transmitting FT8 example 50Hz in 3minutes.jpg
Hi, today I´ve tried out WSPR with my FDT86256 Rig, and could not see any drift at all.
That was with Full 5W Out, and as you know WSPR Transmissions have a duration of 2 Minutes:

Code: Select all

Timestamp		Call		MHz		SNR	Drift	Grid		Pwr	Reporter	RGrid	km	az	Mode
 2022-07-17 11:40 	 DL2MAN 	 7.040098 	 -1 	 0 	 JN59xh 	 5 	 S51RS 	 JN86cq 	 430 	 131 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040077 	 -12 	 0 	 JN59xh 	 5 	 OE9BKJ 	 JN47ul 	 263 	 220 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040073 	 +7 	 -1 	 JN59xh 	 5 	 DL9GCW 	 JN48vc 	 208 	 231 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040086 	 -28 	 -1 	 JN59xh 	 5 	 DF8OE 	 JO42jr 	 440 	 331 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040079 	 -20 	 0 	 JN59xh 	 5 	 SM7KHA 	 JO65kv 	 735 	 4 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040065 	 -23 	 0 	 JN59xh 	 5 	 SA6BSS/FLY 	 JO68sc 	 983 	 5 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040063 	 -22 	 -1 	 JN59xh 	 5 	 M0MVA 	 IO81 	 1088 	 288 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040064 	 +3 	 -1 	 JN59xh 	 5 	 DL4TOM 	 JN59it 	 106 	 302 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040073 	 -20 	 0 	 JN59xh 	 5 	 HA8HL/P 	 JN96ov 	 601 	 114 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040063 	 0 	 0 	 JN59xh 	 5 	 SQ3E 	 JO71rq 	 362 	 42 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040067 	 -16 	 -1 	 JN59xh 	 5 	 G4HZX 	 IO91xk 	 882 	 290 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040069 	 +1 	 -1 	 JN59xh 	 5 	 DJ6DK 	 JN48fw 	 258 	 262 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040098 	 -7 	 -1 	 JN59xh 	 5 	 SWL1/JO21 	 JO21jn 	 566 	 299 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040079 	 +6 	 0 	 JN59xh 	 5 	 PH4RTM 	 JO31ai 	 477 	 301 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040086 	 -10 	 -1 	 JN59xh 	 5 	 DD5XX 	 JN48ps 	 203 	 254 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040064 	 -13 	 0 	 JN59xh 	 5 	 G4FLQ/1 	 IO95ga 	 1111 	 310 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040067 	 -7 	 -1 	 JN59xh 	 5 	 F4VTQ 	 JN28ux 	 456 	 268 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040059 	 +9 	 -1 	 JN59xh 	 5 	 PI4THT 	 JO32kf 	 482 	 314 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040090 	 -16 	 0 	 JN59xh 	 5 	 DN4BAS 	 JO62sq 	 391 	 16 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040107 	 -10 	 0 	 JN59xh 	 5 	 PD1V 	 JO21pi 	 525 	 298 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040065 	 -23 	 -1 	 JN59xh 	 5 	 YO3WL 	 KN34ah 	 1205 	 112 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040067 	 -7 	 -1 	 JN59xh 	 5 	 DK8JP/1 	 JO31gk 	 451 	 304 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040064 	 -13 	 0 	 JN59xh 	 5 	 G4FLQ/2 	 IO95gb 	 1113 	 310 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040092 	 -10 	 -1 	 JN59xh 	 5 	 DB9SH 	 JN58tc 	 137 	 190 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040069 	 +8 	 0 	 JN59xh 	 5 	 DL4RU 	 JN69cr 	 50 	 21 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040066 	 -17 	 -1 	 JN59xh 	 5 	 DC7TO 	 JO62qk 	 361 	 15 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040163 	 -23 	 -1 	 JN59xh 	 5 	 MW0CWF 	 IO81ik 	 1105 	 288 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040067 	 -22 	 0 	 JN59xh 	 5 	 GM4SJB/H 	 IO88ba 	 1417 	 319 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040087 	 +1 	 0 	 JN59xh 	 5 	 PA0SLT/4 	 JO33kg 	 564 	 323 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040111 	 -4 	 -1 	 JN59xh 	 5 	 DB9OH 	 JO52ji 	 348 	 347 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040067 	 +7 	 -1 	 JN59xh 	 5 	 DK8JP 	 JO31gk 	 451 	 304 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040069 	 +4 	 0 	 JN59xh 	 5 	 DL2JA 	 JN58vk 	 98 	 187 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040064 	 -27 	 0 	 JN59xh 	 5 	 M0LMH 	 IO93gx 	 1059 	 304 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040061 	 -28 	 -1 	 JN59xh 	 5 	 2E0DSS 	 IO82xl 	 1041 	 295 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040098 	 +2 	 0 	 JN59xh 	 5 	 DL0HMK 	 JO54af 	 562 	 347 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040064 	 -14 	 0 	 JN59xh 	 5 	 MM3NDH 	 IO86ha 	 1270 	 312 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040073 	 -3 	 -1 	 JN59xh 	 5 	 DK8JP/2 	 JO31gk 	 451 	 304 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040069 	 -6 	 0 	 JN59xh 	 5 	 OK2IP 	 JN89ef 	 321 	 90 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040065 	 -9 	 0 	 JN59xh 	 5 	 SA7LIL 	 JO66ib 	 752 	 4 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040071 	 +11 	 0 	 JN59xh 	 5 	 DL/PA0EHG 	 JO32sq 	 486 	 322 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040064 	 +4 	 0 	 JN59xh 	 5 	 DC1RDB 	 JN58ss 	 67 	 207 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040065 	 -24 	 -1 	 JN59xh 	 5 	 HB9GVC/RX 	 JN47ki 	 315 	 227 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040061 	 -15 	 -1 	 JN59xh 	 5 	 2E0ILY/KIWI 	 IO82qv 	 1091 	 297 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040064 	 -15 	 -1 	 JN59xh 	 5 	 DL2ZZ 	 JO31lo 	 436 	 308 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040068 	 -16 	 0 	 JN59xh 	 5 	 GM4SJB/V 	 IO88ba 	 1417 	 319 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040069 	 -20 	 -1 	 JN59xh 	 5 	 PA3WLE 	 JO22is 	 636 	 310 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040068 	 +11 	 -1 	 JN59xh 	 5 	 DJ9PC 	 JN59po 	 58 	 304 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040067 	 +10 	 0 	 JN59xh 	 5 	 DK8FT 	 JN58oe 	 137 	 204 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040064 	 +1 	 -1 	 JN59xh 	 5 	 ON4WS 	 JO20hi 	 538 	 285 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040056 	 -1 	 -1 	 JN59xh 	 5 	 DG2NPE 	 JN59tw 	 74 	 341 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040050 	 -17 	 -1 	 JN59xh 	 5 	 DL5XL 	 JO43gi 	 508 	 333 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040071 	 -7 	 0 	 JN59xh 	 5 	 PA0RWT/3 	 JO33lg 	 561 	 324 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040064 	 -8 	 -1 	 JN59xh 	 5 	 I0UVN 	 JN61nl 	 876 	 174 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040069 	 -24 	 0 	 JN59xh 	 5 	 G8NXD 	 IO70je 	 1234 	 281 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040068 	 +1 	 -1 	 JN59xh 	 5 	 DK6UG 	 JN49cm 	 272 	 276 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040065 	 +2 	 -1 	 JN59xh 	 5 	 PA3ABK 	 JO21it 	 582 	 301 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040071 	 +5 	 0 	 JN59xh 	 5 	 DF1DR 	 JO31rm 	 402 	 309 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040064 	 +8 	 -1 	 JN59xh 	 5 	 HB9TMC 	 JN46lj 	 394 	 216 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040065 	 -4 	 0 	 JN59xh 	 5 	 PA4HJH 	 JO22su 	 596 	 314 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040064 	 +3 	 -1 	 JN59xh 	 5 	 OE9TAV 	 JN47tk 	 270 	 220 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040083 	 -14 	 0 	 JN59xh 	 5 	 IZ6QQT 	 JN63hr 	 623 	 175 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040064 	 -14 	 -1 	 JN59xh 	 5 	 PA1JMS 	 JO21cx 	 621 	 301 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040064 	 -7 	 -1 	 JN59xh 	 5 	 IZ2442SWL 	 JN45ns 	 447 	 209 	 2 
 2022-07-17 11:40 	 DL2MAN 	 7.040077 	 +4 	 0 	 JN59xh 	 5 	 ON4AWM0 	 JO20ot 	 510 	 292 	 2 
So maybe it´s related to your specific hardware ?
Where did you get your Kit/Rig from. Maybe the selected crystal is just a bad one.

73 Manuel; DL2MAN
DL2RMM
 

Posts: 15
Joined: 07 Jan 2022, 21:15

Re: TCXO upgrade

Post by DL2RMM »

DL2MAN wrote: 17 Jul 2022, 11:51
....
So maybe it´s related to your specific hardware ?
Where did you get your Kit/Rig from. Maybe the selected crystal is just a bad one.

73 Manuel; DL2MAN
Hi Manuel,

my kit (=crystal) was part of the first german group buy (DC8LZ).
I continued some FT8 "drift testing" on the upper bands and it seems the drift gets stronger with higher frequency:
20meters => 2Hz/min
17meters => 3Hz/min
15meters => 5Hz/min (worst efficiency, stronger heat generation by FDT86256)
12meters => 4Hz/min
10meters => 8Hz/min

The testing was done with 15sec on/off FT8 cycles for 10minutes each.

The biggest "jump" happens after the first 15sec transmit cycles and stabilizes after ~5 min at 1-2Hz/min.

There is absolutely no drift when only receiving.

Do you have a high band kit with FDT86256 that you could test on 10meters (for comparison) ?

73 de Jens, DL2RMM
N4XTL
 

Posts: 19
Joined: 08 Jul 2022, 01:44

Re: TCXO upgrade

Post by N4XTL »

Ohwenzelph wrote: 12 Jul 2022, 16:04 Do you have an OSH Park file for the board? And what are you going to use for C1andC2?

Also, the the processor seems to connect to two sides of the crystal with two lines but the oscillator only has one "out" point, so how do you hook it up?
Once I test the mod and verify it works, I will post links and pictures. I don't want to recommend this until I know it works.

The TCXO only has a single output, which will be fed into the XA pin of the Si5351. C1 and C2 are both 100 nF. C1 is just a bypass cap for the power rail, and C2 is a series capacitor on the clock signal line going into XA as recommended in the Si5351 datasheet. (The XB pin on the Si5351, the other pin used for a normal crystal, will be unused and left open as recommended in the datasheet)

I have the TCXOs on hand already and the PCBs shipped today. Looking forward to trying this out.
N4XTL
 

Posts: 19
Joined: 08 Jul 2022, 01:44

Re: TCXO upgrade

Post by N4XTL »

I've had some success with my TCXO upgrade board. There are a few things I want to revise, but the upgrade is installed and working well in one of my radios.

This is the assembled board. I ordered the PCB from OSHPark with their 0.8mm option, so the complete board is very low profile and poses no risk of shorting against the RF board when installed.
Image

I tested the board before installing it in my radio. I verified the output waveform on an oscilloscope, a nice 1.2 Vpp clipped sine wave. I also measured the frequency on a calibrated counter. This TCXO is about 30 Hz or 1.1 ppm low. TCXOs aren't perfect but that's much better initial frequency accuracy than I got from the crystal.
Image

Next step is removing the default 27 MHz crystal, Y1. This is the scary part of course but I got the crystal off without causing any damage. Labeled are the three pads that the upgrade PCB connects too for power, output and ground.
Image

I used some double sided tape to secure the upgrade PCB to the main board, aligning the castellated vias with the three pads they connect to. I wanted something easily reversible in case I had to troubleshoot. I think some epoxy or hot melt glue could be used to further secure the PCB. Notice that the PCB is slightly crooked due to interference from U9. I will fix this in the next revision with a small cutout there.
Image

Next I soldered the castellated vias to the three pads using small tinned wire.
Image

Finally I powered on the radio and tested it with no issues. A frequency calibration value of 27000000 was perfectly acceptable, though 26999950 was slightly more accurate. This made sense given my measured value of the TCXO output before install. Either way, much better initial frequency accuracy than the crystal my board came with.

Of course the true value of the TCXO is stability over a wide temperate range. This will take some more testing and comparison of a stock unit versus this "upgraded" unit.

I need to revise the upgrade PCB before sharing it, but I'm happy with where I'm at right now. Do I have the only (tr)uSDX with a TCXO right now? :D Who knows.
mojoe
 

Posts: 9
Joined: 17 Jul 2022, 00:16

Re: TCXO upgrade

Post by mojoe »

Very nice. Thanks for the update.

Being extra cautious, I'd be inclined to put a piece of Kapton tape on the top and bottom. Then there is no chance of anything shorting. But I have plenty of Kapton tape.
mojoe
 

Posts: 9
Joined: 17 Jul 2022, 00:16

Re: TCXO upgrade

Post by mojoe »

Just a thought - is it too much to ask if those three solder pads are 0.1" apart (or close enough)? If so, use through hole instead of castellated, and you can use a 3-pin header for a more secure connection.
N4XTL
 

Posts: 19
Joined: 08 Jul 2022, 01:44

Re: TCXO upgrade

Post by N4XTL »

mojoe wrote: 24 Jul 2022, 06:31 Just a thought - is it too much to ask if those three solder pads are 0.1" apart (or close enough)? If so, use through hole instead of castellated, and you can use a 3-pin header for a more secure connection.
The spacing of the castellated vias currently is 2.2mm, so just a bit narrower than 0.1"/2.54mm. I checked with a piece of header and 0.1" spacing would just barely work with the pads, hitting the outer edges of VDD and GND for soldering. The problem is, standard straight through header would add a lot of thickness to the board, and the overhang of the mod PCB with through holes instead of castellations would make it difficult to solder to the pads.

I might be able to do a piece of right angle header, hanging over the side of the board, and soldered surface mount style to minimize height.
NEW BOY
 

Posts: 16
Joined: 28 Mar 2022, 15:50

Re: TCXO upgrade

Post by NEW BOY »

Hey, N4XTL
Your idea is great, is your latest PCB revision ready?
Also can I ask about the role of C1 and C2?
73!
Ohwenzelph
 

Posts: 105
Joined: 01 Jan 2022, 03:47

Re: TCXO upgrade

Post by Ohwenzelph »

"C1 and C2 are both 100 nF. C1 is just a bypass cap for the power rail, and C2 is a series capacitor on the clock signal line going into XA as recommended in the Si5351 datasheet. (The XB pin on the Si5351, the other pin used for a normal crystal, will be unused and left open as recommended in the datasheet)"
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