SM 5 BSZ - Dynamic range measurements at the eleventh International EME conference, New Jersey, USA, August 2004.
(Aug 13 2004)

Spectral purity of a continuous carrier.

The unit under test was connected to a high power attenuator followed by an ordinary step attenuator which was connected to the RXHFA or RX144 unit. The step attenuator was adjusted to place the signal approximately a few dB below A/D saturation.

A screen dump from the Linrad display in tx test mode was saved for each unit showing the spectrum centered about 25 kHz below the carrier. To see these spectra, click on the links below:

Crystal oscillator 14 MHz (reference)
FT-1000D
FT-736R
FT-817
FT-847
FT-897
IC-765
Orion
TS-2000

The spectral purity of a continuous carrier is listed in table 1. In this table spurious signals are not included. For spurs, look at the screen dumps. Note that the mirror image that is produced because RX2500 is a direct conversion receiver is located symmetrically with respect to the spectrum midpoint. This receiver/Linrad spur is suppressed by about 60 dB in these measurements except for the crystal oscillator which was measured several weeks earlier, immediately after Linrad was calibrated.


 Model/ser.        Band        Noise floor in -dBc/Hz  
                   (MHz)    5kHz  10kHz  15kHz  20kHz  50kHz 
IC-765(02576)        14    121.3  126.7  128.4  129.0  130.1
FT-1000D(3G330126)   14    107.7  115.0  117.8  120.0  124.7
FT-736(9E260294)    144    115.7  123.7  126.7  128.4  130.8
FT-817(1D240059)    144    101.7  110.6  114.8  118.0  126.7
FT-817(1E270433)    144    101.0  109.6  114.2  117.4  126.0
FT-817(1E270433)     14    107.3  115.2  119.6  122.8  128.8
FT-847(81100231)     14    105.6  117.2  124.9  129.3  136.4
FT-847(81100231)    144     94.3  107.3  112.7  116.1  125.2
FT-897               14    109.9  120.2  125.8  128.4  127.3
Orion(03C10433)      14    128.2  127.1  126.2  125.2  119.8
TS-2000(30400028)    14    108.6  117.8  119.6  121.1  124.1
TS-2000(30400028    144    105.3  115.3  119.8  122.6  131.0
Table 1. Noise floor at different frequency separations from a carrier.


The power regulation from the front panel in FT-817 uses the ALC loop. This is common in commercial amateur equipment and it causes problems by broadening the modulated signal. The ALC design in FT-817 is unusually bad as one can see from the spectra of modulated signals below. The ALC loop self-oscillates continuously at reduced power (0.5W) giving a sideband noise level of about -95 dBc/Hz at 10 kHz separation on 14 MHz. One example is included in the spectra linked to above.

Spectral purity of voice SSB transmissions.

One or several screen dumps from the Linrad display in tx test mode were saved for each unit showing the spectrum centered 25 kHz from the SSB signal. To see these spectra, click on the links below:

FT-1000D
FT-736R
FT-817
FT-847
FT-897
IC765
Orion
TS-2000

Modern transceivers typically produce broad SSB signals with a lot of splatter in surrounding channels when operated in "normal" mode with the ALC active. Table 2 shows the peak splatter level in 2.4 kHz bandwidth in dB below the peak power in 2.4 kHz bandwidth. Since the mechanism of the interference typically is too much gain in the ALC loops with an associated oscillatory behaviour of the ALC action, the interference sometimes has equidistant maxima. To give a true representation of the interference, table 2 shows the highest interference level at or above each frequency separation.


                                Splatter level below PEP at      
 Model                  Band   5kHz 10kHz 15kHz 20kHz 30kHz 40kHz 50kHz  
                        (MHz)  (dB)  (dB)  (dB)  (dB)  (dB)  (dB)  (dB)
FT-1000D (3G3300126)      14    39    59    66    66    75    77    79
FT-736R (9E260294)       144    31    50    55    59    67    74    81
FT-817 (1E270433) 0.5W    14    15    15    15    15    15    29    29
FT-817 (1D240059) 0.5W    14    13    13    13    13    13    27    27
FT-817 (1E270433) 0.5W   144    20    20    20    20    31    31    40
FT-817 (1D240059) 0.5W   144    15    15    15    15    32    32    32 
FT-817 (1E270433) 5W      14    13    13    13    13    13    26    26
FT-817 (1E270433) 5W     144    40    49    49    49    61    61    75
FT-817 (1D240059) 5W     144    36    44    44    44    56    56    67
FT-847 (81100231) 2W     144    19    19    19    38    38    41    41   
FT-847 (81100231) lowpow  14    18    18    18    18    35    40    40
FT-847 (81100231) maxpow  14    27    27    27    34    42    50    54
FT-897                    14    34    52    68    74    80    80    82
IC-765 (02576) 40W mic    14    47    59    67    75    77    80    80
IC-765 (02576) 40W RF     14    36    52    59    64    64    64    64
IC-765 (02576) full pwr   14    34    37    37    37    37    37    37
Orion (03C10433)  on      14    37    41    46    47    53    58    64
Orion (03C10433) off      14    39    45    48    51    56    60    66
TS-2000(30400028)        144    44    53    63    76    85    88    89
TS-2000(30400028)         14    31    45    57    66    74    75    75
 
Table 2. Peak splatter level in dB below peak power at or above different frequency separations from a SSB voice signal. For details, look at the spectra.


The ALC of the FT-817 is horrible. This rig should not be used without an external fixed voltage into the ALC circuit to keep the gain constantly below the level where the ALC becomes active. This is actually a good idea for all transmitters. The good performance of the IC-765 with the power turned down using the mic gain shows what performance one can expect with an external speech processor that would limit the power on the audio frequency side. This performance can not be obtained without an external processor because it is very difficult to keep constant peak power of the human voice. The IC-765 suffers from some instability of unknown origin that produces strong sidebands about 60 kHz above the main signal. The speech processor of the Orion does not change the spectrum of the unit significantly.

Spectral purity of keyed CW transmissions.

An over-active ALC causes keying clicks with a characteristic spectral pattern. Such interference is typically worse when the power level is brought down by use of the power setting on the front panel menu. ALC generated keying clicks can be eliminated by a fixed voltage into the ALC input. At the New Jersey EME meeting, spectra of keyed transmissions were taken both at full power and at reduced power for several transceivers and for some the keying waveform was captured in the time domain.

FT-1000D
FT-736R
FT-817
FT-847
FT-897
IC-765
Orion
TS-2000

Keying clicks are seen in these spectra as a separation between the peak power (green) and average power (red) above 12 dB. The level of the keying clicks is listed in table 3.


 Model  (ser.no)          Band       Keying clicks. -dBc in 2.4 kHz.  
                         (MHz)  5kHz 10kHz 15kHz 20kHz 30kHz 40kHz 50kHz
FT1000D (3G330126)         14    65    72    75    77    79    80    81
FT-736R (9E260294)        144    28    33    41    46    46    53    56
FT-817 (1E270433) 5W       14    12    12    12    12    12    24    24
FT-817 (1E270433) 5W      144    40    47    50    52    56    60    62
FT-817 (1D240059) 5W      144    54    66    71    74    78    81    83
FT-817 (1E270433) 0.5W     14    10    10    10    10    10    22    22
FT-817 (1D240059) 0.5W     14    11    11    11    11    11    22    22
FT-817 (1E270433) 0.5W    144    20    20    20    20    27    27    37
FT-817 (1D240059) 0.5W    144    42    45    45    47    55    57    59
FT-847 (81100231) maxpow  144    45    59   N69   N73   N77   N80   N82
FT-847 (81100231) 2W      144    14    14    14    22    22    31    39
FT-847 (81100231)          14     7    10    11    12    14    15    15
FT-897                     14    42    70    82    82    82    82    82
IC-765 (02576)             14    33    43    54    56    59    62    64
Orion (03C10433)  10W      14    44    51    59    65   N75   N75   N75
Orion (03C10433) 100W      14    47    52    56    61    69   N76   N76
TS-2000 (30400028)        144   N62   N71   N75   N79   N82   N84   N87
TS-2000 (30400028)         14    50    72    76    76    76    76    76 
Reasonable                      >60   >67   >70   >74   >76   >78   >80
Table 3. Peak power in 2.4 kHz bandwidth in dB below the carrier for keyed transmitters. The table gives the worst level at or above the listed frequency. Numbers preceeded by N is peak power values that are consistent with (about 12 dB above) the average power level, which is an indication that keying clicks are not present. For details, see the spectrum graphs.


Table 3 is discouraging as this kind of tables usually are. The FT847 generates wideband pulses at the key-up transition for unknown reasons. FT-817 has an unstable ALC that easily oscillates. On 14 MHz the FT-847 suffers from a frequency jump of about 20 kHz at key-down. It seems the VCO looses locking and the output is gated with fast rise times while the VCO is unlocked. The keying clicks are strongly assymmetrical, much stronger above the carrier than below. The FT847 also suffers from strong oscillations in the ALC system on 14 MHz. The TenTec Orion, which has a computer generated waveform that should give a very narrow spectrum suffers from keying clicks due to the ALC which is not well designed. The Orion problem can probably be cured with a software update.

The line "Reasonable" in table 3 represents what I think are reasonable numbers for modern transceivers. These numbers do not allow for much keying clicks, they represent what modern rigs with a sideband noise level of -120 dBc/Hz at 20 kHz would perform like if they incorporate reasonable keying.

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