SM 5 BSZ - Dynamic range measurements in Käringsundbyn, OH0, June 2004
(June 26 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 1 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 25kHz from the carrier. To see these spectra, click on the links below:

Crystal oscillator 14 MHz (reference)
FT-726R (mod) 144 MHz (SM5IOT)
FT-857 144 MHz (SM6OEW)
FT-857D 144 MHz (OH1ZAA)
IC910H 144 MHz (ser no 01533)
K2 14 MHz (OH3MCK)
K2+conv 144 MHz (OH3MCK)
TR9130 144 MHz (SM4LMV)

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             Band      Noise floor in -dBc/Hz  
                  (MHz)    5kHz  10kHz  15kHz  20kHz  50kHz 
FT726R(mod,SM5IOT) 144    111.3  123.6  128.2  129.5  130.7
FT857 (SM6OEW)     144    101.2  111.2  116.1  119.6  126.7
FT857D (OH1ZAA)    144    101.2  111.4  116.5  119.8  126.9
IC706MKIIG (SM6NZB)144    103.6  112.0  115.9  118.1  125.6
IC910H (01533)     144     96.9  106.2  111.1  113.7  121.3
K2 (OH3MCK)         14    114.6  117.8  118.9  119.1  120.0
K2+conv (OH3MCK)   144    113.7  119.3  121.9  123.9  128.0
TR9130 (SM4LMV)    144    116.3  125.6  129.7  132.3  135.9
Table 1. Noise floor at different frequency separations from a carrier.

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-726R (mod) 144 MHz (SM5IOT)
FT-857 144 MHz (SM6OEW)
FT-857D 144 MHz (OH1ZAA)
IC910H 144 MHz (ser no 01533)
TR9130 144 MHz (SM4LMV)

Modern transceivers typically produce broad SSB signals with a lot of splatter in surrounding channels when operated in "normal" mode with the ALC active. The IC706MKIIG was tested with a fixed negative voltage at the ALC input. When power was reduced this way the emitted spectrum was free of splatter. 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)
FT726R,mod,SM5IOT full power   144     9     9     9     9    19    21    23
FT726R,mod,SM5IOT 50% power    144    32    48    55    58    61    64    66 
FT857,SM6OEW                   144    30    50    54    60    69    75    79
FT857D,OH1ZAA                  144    33    52    60    66    71    79    84
IC706MKIIG,SM6NZB,full power   144    28    48    58    62    75    81    84
IC706MKIIG,SM6NZB,ALC=-2.13V   144    46    68    76    77    79    79    79
IC910H,ser=01533               144    32    53    64    68    69    69    69
TR9130,SM4LMV                  144    33    42    50    56    67    75    82
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.

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 Käringsundbyn, spectra of keyed transmissions were taken at full power only to get some idea of typical interference levels under normal operation of the transceivers under test. Click on the links below to see keyed spectra and in some cases keying waveforms in the time domain.

FT-726R (mod) 144 MHz (SM5IOT)
FT-857 144 MHz (SM6OEW)
FT-857D 144 MHz (OH1ZAA)
IC910H 144 MHz (ser no 01533)
K2 14 MHz (OH3MCK)
K2+conv 144 MHz (OH3MCK)
TR9130 144 MHz (SM4LMV)

Keying clicks are seen in these spectra as a separation between the peak power (green) and average power (red) above 12 dB. As can be seen in these links, the FT726R(mod) is unacceptable because of some non-linearity that happens near full power. Maybe this unit suffers from some kind of parasitic oscillations? It could also be some problem in the keying or ALC circuits. The very bad performance in SSB at full power is probably caused by the same phenomenon.

The K2 has a problem when operated with the 28 to 144 MHz transverter. Probably the transverter switches between rx and tx while RF power is sent into the unit on 28 MHz. The TR9130 has unacceptable keying clicks when hand keyed at normal speed. When keyed at 40 hz the keying clicks are much weaker and caused by a far to rapid fall time. The reason for the keying clicks to be much worse at normal keying speeds is probably in the way the ALC regulates the power.

Some of the transceivers were also tested in a narrow frequency range. These spectra are linked to below.

FT857D, OH1ZAA, narrow
FT857, SM6OEW, narrow
IC910H, ser 01533, narrow

The level of the keying clicks is listed in table 3. The data is from the wideband spectra and shows the peak power of the keying click in dB below the carrier.

 Model                        Band       Keying clicks. -dBc in 2.4 kHz.  
                              (MHz)  5kHz 10kHz 15kHz 20kHz 30kHz 40kHz 50kHz 
FT726R,mod,SM5IOT              144    30    38    44    47    52    57    61
FT857,SM6OEW                   144    39    61    73   N76   N79   N81   N83
FT857D,OH1ZAA                  144    31    56    65    75   N80   N82   N82
IC706MKIIG,SM6NZB,full power   144    59    69    73    75   N79   N81   N82
IC706MKIIG,SM6NZB,power="4"    144    28    54    66    75    80   N81   N81
IC706MKIIG,SM6NZB,ALC=-2.13V   144    60    69    73    75   N78   N79   N81
IC910H,ser=01533               144    54    64    68    70    70    70    70
K2                              14   N71   N75   N77   N77   N77   N77   N77
K2+conv 28->144                144    17    19    23    24    25    28    43
TR9130,SM4LMV                  144    28    35    38    41    44    46    48
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 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 K2 has fine keying, the ICOM transceivers are reasonable as long as power is not reduced by use of the front panel menu setting. The FT857/FT857D has too fast rise and fall times, probably because the output power vs keying voltage is strongly non-linear. This can be seen in the key-down waveform in the time domain. The TR9130, FT726R and K2+conv produce very strong keying clicks and these rigs should not be used on the air until the reason is found and the problem cured.

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.

Receiver dynamic range

Receiver measurements take more time than transmitter measurements. At the Käringsundbyn VHF meeting 2004, I only looked at the receivers of the K2 and of the FT857D.

The noise figures of the K2 and the FT857D were was measured as 23.4 and 6.9 dB respectively. The power level of an off channel signal required to reduce the S/N of a weak signal by 3 dB is listed in table 4.

                      Power for 3 dB S/N loss         Equivalent sideband noise level
Model       Band     @10kHz   @20kHz    @100kHz        @10kHz   @20kHz   @100kHz
            (MHz)    (dBm)    (dBm)    (dBm)          (dBc/Hz) (dBc/Hz)  (dBc/Hz)   
FT857D       144     -54.5    -46.0    -34.7           -112.6   -121.1    -132.4      
K2            14     -27.8    -26.1    -20.1           -122.8   -124.5      -

Table 4. Receiver dynamic range. P is the level of a strong signal that reduces S/N of a weak signal by 3 dB. The corresponding LO sideband noise level is listed in the last column. The K2 is limited by saturation at 100 kHz so no equivalent noise floor is given.

The third order intercept point was found to be -5 dBm for the FT857D. IP3 was not measured for the K2, but with 1 dB compression at about -23 dBm one can estimate IP3 to something like -10 dBm, not very impressive considering the large noise figure.

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