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CRuni-NG:

A very small TCXO (Temperature Compensated Crystal Oscillator) based synthesizer unit for many ICOM transceivers, but virtually compatible with many other radios.

The CRuni-NG
The bottom side of CRuni-NG


Based on a Si5351 CMOS synthesizer with a high stability TCXO as reference clock, the CRuni-NG is a programmable synthesizer designed as a replacement for many oscillators with “exotic” output frequencies or hard to find as standard TCXO’s, especially the ICOM CR338, CR282 and CR293 OCXO crystal units:


The CRuni-NG has the same dimension and pin assignment as the CR338 and CR282, so it can replace both devices 1:1. Even the fine frequency calibration by the transceiver is still possible with the CRuni-NG.

A list of transceivers, where the CRuni-NG can be installed instead of a CR338 (frequency=32MHz):

  • IC-7400
  • IC-746 PRO
  • IC-707
  • IC-718
  • IC-77
  • IC-78
  • IC-970E/H

Transceivers, where the CRuni-NG can be installed instead of a CR282 (frequency=30MHz):

  • IC-706MKIIG
  • IC-706
  • IC-775
  • IC-765
  • IC-746
  • IC-732
  • IC-736
  • IC-737
  • IC-R75
  • IC-R72

Transceivers, where the CRuni-NG can be installed, using an adapter board, instead of a CR293 (frequency=30.2MHz):

  • IC-910
  • IC-820
  • IC-821
  • IC-R8500
CR293 adapter board for CRuni-NG

Furthermore the programmable output frequency up to 160MHz, the small size, wide supply voltage range and standard pinout (4 pins with the same footprint of a DIL14 socket) allows the flexible use of CRuni-NG as high stability reference clock source for many other radios where “exotic” reference clock frequencies are used.



The CRuni-NG was designed for a improvement of the frequency stability and accuracy of many Icom rigs. If you looking for a solution to keep the frequency of your rig stable over a wide temperature range, then a CRuni-NG is the right choise!

How it work the CRuni-NG ?


It was designed around a Si5351 CMOS synthesizer with a high stability TCXO as reference clock source. The supply for the Si5351 and reference clock are provided from a active denoiser circuit, which permit to achiev a low level of in-band phase noise of the synthesized output signal. The TCXO module from Murata providing a high degree of frequency stability of ±0,28ppm over a wide temperature range. Optionally is possible to use for example, a SiTime Precision Super-TCXO with an amazing stability of ±0,1ppm. The microcontroller configure the synthesizer very fast at power on, to avoid critical startup locks on some ICOM transceivers. The initial firmware programming are provided through ISP-interface on a 6 pin header.

There are 4 user-selectable startup frequencies (defaults: 30Mhz, 30.2MHz and 32MHz, the 4th frequency is reserved) in the firmware, but these values can be replaced with any value between 8kHz and 160Mhz. The frequency selection can be done through two solder jumpers on the upper board:

  • SJ1+SJ3 open: 32MHz (CR338-mode)
  • SJ3 close: 30MHz (CR282-mode)
  • SJ1 close: 30.2MHz (CR293-mode)
  • SJ1+SJ3 close: reserved frequency

The control voltage input VC get the fine frequency calibration from the transceiver. Furthermore are present a precision multiturn trimmer for a fine frequency calibration for any other application without external control voltage.

The fine frequency calibration trimmer position:


CRuni-NG Specifications:

  • Output frequency: 30MHz, 30.2MHz or 32MHz (programmable for any value from 8kHz up to 160 MHz)
  • Output level: 350 mVpp at 50 Ohm
  • Reference TCXO Frequency stability: ±0,28ppm@20MHz (or with extra high stability option: ±0,1ppm)
  • Output Frequency stability: ±0,42ppm@30MHz (or ±0,15ppm@30MHz with extra high stability option: ±0,1ppm)
  • Operating Temperature Range: -20 to 70°C
  • power supply requirements: 5,5 to 24 VDC, max. 36mA (or with extra high stability option: 10,5 to 16 VDC, max. 90mA)
  • Frequency fine adjustment range: 90Hz (±5ppm) (or with extra high stability option: 100Hz)
  • Module size (LxWxH):  25x15x13mm
CRuni-NG Pinout


The CRuni-NG is 100% compatible with the high stability crystal units from ICOM, where the same dimensions and 4 pins are in the same location permit a easy installation.

Another important feature of the CRuni-NG is the high quality multiturn trimmer, which permit a fine frequency alignment from the top without removing the unit from the transceiver.


Performance tests:


The CRuni-NG output signal spectrum (on a R&S FSEA30, at it’s highest input sensivity):

RBW=50Hz SPAN=400kHz
RBW=10Hz SPAN=2kHz

Performance test on a IC-7400:

These tests was done on a ICOM IC-7400 and a HP 8648C signal generator (output frequency = 144.300MHz) with a external high precision 10MHz Rubidium reference clock, and the radio tuned on 144.299 MHz USB. I have choose the VHF band because the frequency drift of a transceiver are more noticable at the highest frequency band. The audio output from the IC-7400 is sampled with a TinyGate USB interface on a pc where running Spectrum Lab.

If have made a comparison test between three different reference clock sources on a ICOM IC-7400:

  1. Stock crystal CR337
  2. High stability crystal option ICOM CR338
  3. CRuni-NG (with a 0,28ppm reference TCXO)

1) IC7400 – Test with stock crystal CR337:

I put the radio (ICOM IC-7400) in a cold basement to bring the temperature down to aprox. 11°C. The graph below with a horizontal scale grid of 10Hz shows the HP 8648C carrier received while the radio is warming up (at the ambient temperature of about 23°C) with the stock crystal oscillator (CR337) installed. The resulting frequency drift at 144MHz is about 220Hz:

warmup frequency drift on a ICOM IC-7400 with stock crystal CR337

2) IC7400 – Test with high stability crystal option ICOM CR338:

I put the radio (ICOM IC-7400) in a cold basement to bring the temperature down to aprox. 11°C. The graph below with a horizontal scale grid of 10Hz shows the HP 8648C carrier received while the radio is warming up (at the ambient temperature of about 23°C) with the high stability crystal option ICOM CR338 installed.

The resulting frequency drift at 144MHz is (after a fast initial huge drift) about 80Hz:

warmup frequency drift on a ICOM IC-7400 with high stability crystal option ICOM CR338

3) IC7400 – Test with CRuni-NG:

I put the radio (ICOM IC-7400) in a cold basement to bring the temperature down to aprox. 11°C. The graph below with a horizontal scale grid of 1Hz (one tenth (!!) of the previous graph above) shows the HP 8648C carrier received while the radio is warming up (at the ambient temperature of about 23°C) with the CRuni-NG installed.

The resulting frequency drift at 144MHz is about 15Hz:

4) IC7400 – Test for frequency stability vs. supply voltage:

On the Icom’s transceivers listed above the supply voltage for the high stabilty crystal units are derived directly from the main supply. There is a noticable supply voltage sensivity in the ICOM’s high stability crystal options CR338 (and probabely also in other models like CR282 and CR293 due the crystal oven control circuit).

The resulting frequency drift at 144MHz when the supply voltage change from 12,5V to 13,5V and then back to 11,5V on a CR338:

CR338 supply voltage sensivity

As comparision here the resulting frequency drift at 144MHz when the supply voltage change from 12,5V to 13,5V and then back to 11,5V on a CRuni-NG, where are no noticable supply voltage sensivity:

CRuni-NG supply voltage sensivity

Performance test on a IC-706MK2G:

If have made a comparison test between two different reference clock sources on a ICOM IC-706MK2G:

  1. Stock crystal CR275
  2. CRuni-NG (with a 0,28ppm reference TCXO)

1) IC706MK2G – Test with stock crystal CR275:

I put the radio (ICOM IC-706MK2G) in a cold basement to bring the temperature down to aprox. 13°C. The graph below with a horizontal scale grid of 10Hz shows the HP 8648C carrier received while the radio is warming up (at the ambient temperature of about 23°C) with the stock crystal oscillator (CR275) installed. The resulting frequency drift at 144MHz is about 170Hz:

warmup frequency drift on a ICOM IC-706MK2G with stock crystal CR275

2) IC706MK2G – Test with CRuni-NG:

I put the radio (ICOM IC-706MK2G) in a cold basement to bring the temperature down to aprox. 13°C. The graph below with a horizontal scale grid of 1Hz (one tenth (!!) of the previous graph above) shows the HP 8648C carrier received while the radio is warming up (at the ambient temperature of about 23°C) with the CRuni-NG installed.

The resulting frequency drift at 144MHz is about 10Hz:

warmup frequency drift on a ICOM IC-706MK2G with the CRuni-NG

Installation example of a CRuni-NG in a ICOM IC-7400:

Remove the stock crystal CR337 (X1901) from the RF-Unit:

2. Insert the CRuni-NG and soldering the 4 pin on the bottom side. Done!


Availability:

The CRuni-NG will be soon available from RF-SYSTEM‘s webshop.

For other questions please send me an email.

Thanks!