# Presentation: 445868

## Responses to Vendor Comments

- DCS MANUFACTURERS MEETING NOVEMBER 9, 2006
- Peter Woolner
- Mitretek Systems
- _[pwoolner@mitretek.org](mailto:pwoolner@mitretek.org)_
- 703-610-1724

## Appreciation

- I want to thank everyone who provided comments to draft Certification Standard. I appreciate the effort you made, even for the comments with which I do not agree. This is the most feedback I have received in the three years I have been working on this task. Your differing viewpoints have helped me improve my own, whether in agreement or disagreement.      Thank you.

## Presentation Content

- The following pages provide my answers and recommendations to all the comments received on the draft CS dated May 26, 2006, EXCEPT comments on section 4.1.1 RF Power Output
- I am preparing a separate proposal for this item and intend to propose reductions of about 6 dB, but with other factors involved

## Clock Description

- It was not intended to change the clock requirements in section 3.1.
- Proposed Correction: Change the text to
- 	“3 symbol periods, first 180°, then 0°, then 180°.” and include the following figure.

- 0

- 180

- 1 symbol period

- 0.5 or 0.25 second of carrier only

- Start of
- FSS

## MOD: Encoder Flush and Turn-off Time

- I do not think it is desirable to specify a ratio for the OFF power.  The present requirement is to be completely off within one millisecond.  If the output power is still dropping after one millisecond, the requirement is NOT met.
- After 1 mS the power should be as low as it gets until the next transmit period
- If 1 mS is too small, it could be increased
- If a minimum “off” power reduction is needed, I think -50 dB is a suitable value (= 1/100,000)

## NEW: Enc Flush & Turn-off Time

- New comment from Sutron implies similar requirement should be added for carrier turn-on time
- I suggest in 3.1 the “Carrier” section read:
- 0.500 ±0.005 seconds for 300 bps
- 0.250 ±0.005 seconds for 1200 bps
- The turn-on time shall be less than 1.0 mS to within 1 dB of the maximum output power that occurs during the carrier-only period

## MODIFIED: SRRC Filter Definition

- Currently stated as Root Raised Cosine filter with β of 1.0, implemented as a 4th order FIR filter with 65 taps or more
- The request was for the Certification Standard to include the type of windowing and filter coefficients
- Microcom agreed to provide, if NOAA contracts them to make the filter change, similar to data on the current filter
- The intent is to adequately define the receive filter that all transmitters must work into – not what the transmit manufacturers must do, which is for them to decide
- Propose: “The DAMS-NT receiver/demodulator will be a Square Root Raise Cosine type with a roll-off factor (α) = 1.0. Details are provided in Appendix (?) of this Certification Standard”

## Reporting Time Accuracy

- Proposal is for 300 and 1200 to be 0.1 sec
- That was my initial proposal too, but:
- Others argued 0.25 sec would result in a longer time available to correct a problem if the GPS time reference was blocked
- Blockage would be less likely if a time mark was included in a DCPI signal
- Recommend 0.25 sec be retained, but see also response to “Inhibiting Transmissions”

## Random Transmission Length

- Current requirement is for a maximum message length of 3/1.5 seconds at 300/1200 bps
- This is heritage from v.1.0b
- Times were empirically derived but appear suitable
- Length limit is for the total transmission
- Change “message length” to “total transmit time”
- If CDMA is shown to be viable for random transmissions, this requirement will need a more thorough review

## Sidebands: Worst Case ACI (1)

- 500 Hz

- 125 Hz

- 125 Hz

- 200 Hz

- 400 Hz

- 25
- dB

- 225 Hz

- Worst Case Alignment for Sideband Interference:

- NTIA
- mask

**WORST**
**SPECTRAL**
**DISTRIBUTION**

## Sidebands: ACI (2)

- Worst ACI is when each channel drifts 125 Hz toward each other
- Assume (Sin(x) / x)2 spectral distribution
- If noise b/w is 200 Hz for 300 bps (and 800 Hz for 1200)
- Integrate channel power over 400 – 600 Hz (300) from carrier frequency and 1600 to 2400 Hz (1200):  C/I = -22 dB (both rates)
- First sidelobe requires 12 dB attenuation below “natural” level to meet NTIA requirement
- C/I0 = -22 - 12 - 10Log(200) = -57 dB/Hz
- Actual distribution is better than (Sin(x) / x)2
- Other N0 is ~ -37 and -43 dB/Hz when near assumed demod limit of 11.7 dB/Hz, so ACI0 is insignificant
- No change is required

## Nameplate Information

- Suggestion was to list antenna type and gain rather than a manufacturer and the antenna part number (e.g. 11 dB Yagi)
- I would prefer to see the designation include polarization “11 dBi RHCP Yagi”

## Inhibiting Transmissions (Timing)

- My suggestion for new wording of 2.1.1:
- The DCPRS must include an algorithm to ensure that transmissions are inhibited whenever it is possible the internal clock differs by more than 0.25 seconds from UTC and it is not possible to obtain an accurate time synchronization from an external source. The algorithm and the time required for 0.25 seconds deviation from UTC shall be included in the Certification test report.
- (Based on Microcom’s proposal with my changes.)

## Frame Synchronization Sequence 

- Proposed Neuman-Hofman sequence for FSS:   000 0110 0100 1010 is only 3 bits different from the current “No Interleaver” FSS
- Only 3 15-bit Neuman-Hofman sequences exist
- The other two are used for the present long & short interleaver identifiers
- Are any long or short interleavers in use?
- If either not used, we can use it for the new CS units
- If both are used, can another sequence be applied or can ambiguity be tolerated?

## Multiple Items

- For GOES ID/DCP address: agree with suggested change to: “...to form four 8-bit bytes”
- For EOT: I do not see any real problem with leaving the binary mode EOT as is
- For short term frequency stability: need a test to show peak instability, not average (as shown by Kaz’s turn-on drift problem)
- Use the test set or commercial test equipment?
- I do not care if 4.4.3 title says “Total” or “RMS”

## Carrier Phase Noise

- In view of the information provided by Microcom, I propose to change 4.4.1 to the following:
- 	The phase noise of the unmodulated carrier shall be equal to, or less than 2.0 degrees RMS when integrated over the range 1.6 Hz to 150 Hz for 300 bps and 6.2 Hz to 600 Hz for 1200 bps. This limit shall be met under any combination of operational conditions.

## NEW: Phase Noise Effects

- 10

- 100

- 1000

- 1

- 10

- 100

- 1000

- 1

- PHASE NOISE

- SIGNAL ENVELOPE

- MATCHING
- RECEIVE
- FILTER

- CARRIER
- LOOP
- BANDWIDTH

## Phase Noise – Revised

- Suggest new wording:
- 	The phase noise of the unmodulated carrier shall be equal to, or less than 2.0 degrees RMS when integrated over the range 1.6 Hz to 150 Hz for 300 bps and 6.2 Hz to 600 Hz for 1200 bps. The integration may be performed over any range that includes these limits, provided the result is less than 2.0 degrees. This limit shall be met under any combination of operational conditions.
-     IF A SINGLE RANGE WITH ROUND NUMBERS IS PREFERRED, I SUGGEST 1 Hz – 1 kHz

## Transmit Spectrum

- Microcom offered three example alternative SA settings but did not use any of them when they proposed new wording to CS section 4.5 c)
- I think either the 10 or 1 Hz RBW example looks to be acceptable, but I believe a standard SA configuration should be required by the CS, otherwise too much variation is possible
- This test must show the requirement is met AND that the procedure will accurately measure the actual emission
- I recommend RBW = 10 Hz, VBW = 100 Hz, Power RMS Averaging, Average count = 25, for which Microcom has estimated a 30 sec capture time
- Is it possible this configuration could miss some spikes?
- Does anyone else wish to propose a different set-up?

## Appendix A

- I am willing to accept the proposals made by Microcom but is it acceptable to the other vendors and the NOAA Test Official?
- I would like to add a statement that any vendor MAY use other test equipment but must prove it has equal or better accuracy
- I would like to add the capability for:
- A better short term stability test
- +?

## Power Supply Voltage Range

- The point was made by a user that removing the present requirement for a defined voltage range would make matching transmitters and data loggers at a site a more difficult task than it would be if the current voltage limits were retained
- Are you manufacturers sure you want to make this change?