# Plans for Receive only board (suggestions needed)

**URL:** <https://discourse.myriadrf.org/t/plans-for-receive-only-board-suggestions-needed/5169>\
**Category:** LimeSDR\
**Created:** [20 September 2019 16:13 UTC](https://discourse.myriadrf.org/t/plans-for-receive-only-board-suggestions-needed/5169 "2019-09-20T16:13:53Z")\
**Posts on this page:** 9\
**Page:** 1

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**Author:** ![Crater](https://avatars.discourse-cdn.com/v4/letter/c/58f4c7/32.png) [@Crater](https://discourse.myriadrf.org/u/Crater)\
**Post date:** [20 September 2019 16:13 UTC](https://discourse.myriadrf.org/t/plans-for-receive-only-board-suggestions-needed/5169/1 "2019-09-20T16:13:53Z")

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Hi All,  
We plan to use the LIMESDR-USB for Radio Astronomy and therefore need only the RX part of the board. We want to modify the board for better performance (making it less noisier). Can you suggest if they will work?

We plan to do the following modifications:

1. Removing the components on the Receive side (Transformers Caps, Resistor on 3 Inputs).
2. Removing the SPDT switch used for TX RX calibrations.
3. Removing the DDR2 IC’s and its Power supplies.(Not sure if this will harm the FPGA itself)
4. Removing the 0 ohm resistor at the output of the LMK00105 IC used for generating the TxPLL\_CLK.

External precautions are:  
Use a Linear Power Supply to feed the external power Input, don’t use the USB supply.  
Recommendations are needed for the best Input Voltage, 6,9,12V ? (the one that generates the least EMI as there are switching power supplies at the input stage)

Thank you very much in advance…

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**Author:** ![martywittrock](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/martywittrock/32/66_2.png) [@martywittrock](https://discourse.myriadrf.org/u/martywittrock)\
**Post date:** [22 September 2019 12:55 UTC](https://discourse.myriadrf.org/t/plans-for-receive-only-board-suggestions-needed/5169/2 "2019-09-22T12:55:46Z")

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@Crater - Alexander,

Before you do anything like that, please check out this post from the RASDR team:

> [@RASDR4 shielded Enclosure Kit for LimeSDR. Radio Astronomy focus via SARA](https://discourse.myriadrf.org/t/rasdr4-shielded-enclosure-kit-for-limesdr-radio-astronomy-focus-via-sara/621):
>
> Announcing RASDR4 Enclosure Kit for LimeSDR The RASDR4 team is pleased to announce details of RASDR4 shielded Enclosure Kit for the LimeSDR and readiness to accept orders. Pictures of the prototype and production components, kit parts, assembly instructions, and ordering information are available at [www.rasdrllc.com](http://www.rasdrllc.com) . If you order a LimeSDR board from the vendor ([www.crowdsupply.com](http://www.crowdsupply.com)), please select the USB Type A connector. Initial RASDR4 Enclosure Kits were announced Jan. 1 ago to SARA memb…

…and this post that specifically talks about board mods:

> [@RF connection: 10 U.FL connectors (6 RX, 4 TX)?](https://discourse.myriadrf.org/t/rf-connection-10-u-fl-connectors-6-rx-4-tx/305/35):
>
> Hi, Here’s a photo of the board, the filters are between the connectors and the Lime chip. Good luck! [[image] ](https://dl.dropboxusercontent.com/s/e4q0ny86htzo365/SAM_1077.JPG?dl=0)

It may speak only to an enclosure for the Lime used for Radio Astronomy, but that group focuses exclusively on that using the LimeSDR. You may want to see what they’ve done prior to doing anything too extreme on your LimeSDR. It always makes my skin crawl when I see anyone suggesting that they’re going to take parts off their LimeSDR board, so PLEASE don’t do that until you’ve spoken to members of that RASDR team that have got this running on their Limes. Doing a search on ‘Radio Astronomy’ in the search tool for the forum will pull up numerous posts by Hams and researchers who have already blazed this trail.

Hope this helps - 73 de Marty, KN0CK

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**Author:** ![Crater](https://avatars.discourse-cdn.com/v4/letter/c/58f4c7/32.png) [@Crater](https://discourse.myriadrf.org/u/Crater)\
**Post date:** [23 September 2019 14:17 UTC](https://discourse.myriadrf.org/t/plans-for-receive-only-board-suggestions-needed/5169/3 "2019-09-23T14:17:37Z")

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Thank you for the suggestions.  
The LIMESDR Case in the link is no longer available. (The Link is dead)  
This link describes the settings to turn off the TX:

> [@LimeSuite TX mode and FFT viewer issues](https://discourse.myriadrf.org/t/limesuite-tx-mode-and-fft-viewer-issues/991/3?u):
>
> I did not want to run that kind of test for a couple of reasons, but I’m glad I did. It revealed a concern and then further testing led to more concerns about LimeSuite. I connected one of the TX ports to an inexpensive, but excellent [analyzer and signal generator](http://www.rf-consultant.com/tpi-1001-b-signal-generator/). (the picture shows the devices, but for a test using signal generation to LimeSDR RX) Without explicitly turning on TX elements, I measured -26 dBm (red line in picture below). This could be a problem for radio astrono…

Their observation was: Even if you turn off the TX there is still a signal around -55 dBm.

Thats why we were considering severing the TXPLL clock to LMS7002m.

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**Author:** ![AA7QQ](https://avatars.discourse-cdn.com/v4/letter/a/13edae/32.png) [@AA7QQ](https://discourse.myriadrf.org/u/AA7QQ)\
**Post date:** [24 September 2019 00:34 UTC](https://discourse.myriadrf.org/t/plans-for-receive-only-board-suggestions-needed/5169/4 "2019-09-24T00:34:32Z")

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Best is to just supply the board with USB3.0.  
If you need to use a supply, no more than 8VDC.

Ed

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**Author:** ![andrewback](https://avatars.discourse-cdn.com/v4/letter/a/22d042/32.png) [@andrewback](https://discourse.myriadrf.org/u/andrewback)\
**Post date:** [24 September 2019 14:23 UTC](https://discourse.myriadrf.org/t/plans-for-receive-only-board-suggestions-needed/5169/5 "2019-09-24T14:23:25Z")

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> [@Crater](#):
>
> Removing the SPDT switch used for TX RX calibrations

If you can nolonger calibrate the receive path I’d have thought this would have an adverse effect on performance.

Maybe @Zack can comment on your proposed modifications.

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**Author:** ![Crater](https://avatars.discourse-cdn.com/v4/letter/c/58f4c7/32.png) [@Crater](https://discourse.myriadrf.org/u/Crater)\
**Post date:** [24 September 2019 16:39 UTC](https://discourse.myriadrf.org/t/plans-for-receive-only-board-suggestions-needed/5169/6 "2019-09-24T16:39:06Z")

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We plan to use the RX1\_L input with the EasyFIX2 applied.  
Reading the schematics, we are not sure if RX1\_L has a calibartion path using the SPDT switch.  
If RX1\_L is on the calibration path can we apply the mods described in the link below?

> [@LimeSDR Mini and Spurious signal around 100 MHz](https://discourse.myriadrf.org/t/limesdr-mini-and-spurious-signal-around-100-mhz/2801/23):
>
> Hi, I want to share some mods that help reducing spurs (especially on 100Mhz) on limesdr-mini : first : increase C17, C18, C28 and C29 from 10pF to 10nF (values are not really critical) : these are decoupling capacitors for DC controlling voltages of RF switches (TX and RX) (sky13411). According to datasheet the typical value is 10pF to provide fastest switching speed (70ns). In lime-mini, we can increase these capacitors to higher values to provide better RF filtering. It seems that these …

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**Author:** ![hobbyrf](https://avatars.discourse-cdn.com/v4/letter/h/898d66/32.png) [@hobbyrf](https://discourse.myriadrf.org/u/hobbyrf)\
**Post date:** [2 October 2019 08:38 UTC](https://discourse.myriadrf.org/t/plans-for-receive-only-board-suggestions-needed/5169/7 "2019-10-02T08:38:33Z")

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These mods are only for the limesdr-mini. I don’t know if the limesdr-usb board have the same issues as the lime-mini.

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**Author:** ![martywittrock](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/martywittrock/32/66_2.png) [@martywittrock](https://discourse.myriadrf.org/u/martywittrock)\
**Post date:** [2 October 2019 20:23 UTC](https://discourse.myriadrf.org/t/plans-for-receive-only-board-suggestions-needed/5169/8 "2019-10-02T20:23:26Z")

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@hobbyrf,

The Easy Fix was employed on the LimeSDR USB model only and does not apply to the Lime Mini at all…I know…I was the first one to apply it in late 2017 and the LimeSDR Mini didn’t show up until early 2018.

73 de Marty, KN0CK

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**Author:** ![hobbyrf](https://avatars.discourse-cdn.com/v4/letter/h/898d66/32.png) [@hobbyrf](https://discourse.myriadrf.org/u/hobbyrf)\
**Post date:** [5 October 2019 14:34 UTC](https://discourse.myriadrf.org/t/plans-for-receive-only-board-suggestions-needed/5169/9 "2019-10-05T14:34:54Z")

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@Martywittrock , you are right for the easy fix (which improves HF reception on lime usb), but I was talking about the mods for reducing 100MHz spurs on lime mini as Crater quotes. 🙂