SM 5 BSZ - Dynamic range measurements at Annaboda May 2005
(June 10 2005)

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 about 25kHz from the carrier. To see these spectra, click on the links below:

Crystal oscillator 14 MHz (reference)
FT-100D 144 MHz
FT-726R 144 MHz
FT-736R 144 MHz
IC-275E 144 MHz
IC-290E 144 MHz
IC-735 14 MHz
R2-CW 144 MHz
TS-700 144 MHz
TS-780 144 MHz

The FT-736R has an ugly spectrum at reduced power levels. Sidetone spurs in the FT-736R at reduced power The link shows a simple cure for the problem.

Like many other transceivers the FT-736R shows a degraded performance when the output power is reduced. Such problems can typically be cured by a reduction of the transmitter gain. Look here for details Effect of tuning on the sideband noise levels in a FT-736R

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.


 Model               Band      Noise floor in -dBc/Hz  
                    (MHz)    5kHz  10kHz  15kHz  20kHz  50kHz 100kHz 150kHz 
FT-100D (1H240100)   144    107.1  113.7  117.2  119.4  126.5   -      -
FT-726R (3H030740)   144    111.9  125.5  129.6  131.6  134.8  140.5  143.1
FT-736R (3J740239)   144    116.6  124.4  126.4  127.5  129.4  133.2  135.6
FT-736R mod1         144    117.2  124.4  126.7  127.6  129.9   -      -
FT-736R mod1,lowpow  144    112.5  113.8  115.3  116.3  123.8   -      -
FT-736R mod2         144    117.2  124.1  127.0  128.1  129.9   -      -
FT-736R mod2,lowpow  144    115.9  119.1  121.1  122.1  128.5   -      -
IC-275E (01744)      144    100.8  112.1  117.3  130.0  138.3  144.5  147.0
IC-290E (01135)      144    113.1  120.3  125.6  127.3  134.3   -      -
IC-735 (08265)       14     117.0  127.9  130.7  132.5  133.7   -      -
R2-CW (223)          144    124.1  132.5  135.4  136.3  136.9  138.8  138.8
TS-700 mod. (161193) 144    116.0  127.2  132.6  133.7  138.4  141.4  140.8
TS-780 (3020029)     144    119.2  129.0  131.6  133.5  136.3  140.1XX140.8
Table 1. Noise floor at different frequency separations from a carrier. For TS700 and TS780 numbers in italic represent the average power of close spaced carriers, the noise floor is much lower, see the spectra linked to above. The TS-780 has a broad maximum in the sideband noise at about 125 kHz offset with nearly 10 dB higher sideband noise compared to 100 and 150 kHz. This is marked with XX in the table


Spectral purity of voice SSB transmissions.

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

FT-726R 144 MHz
FT-736R 144 MHz
IC-275E 144 MHz
IC-735 14 MHz
TS-700 144 MHz

Modern transceivers typically produce broad SSB signals with a lot of splatter in surrounding channels when operated in "normal" mode with the ALC active. Such problems are most common on HF bands where the ALC typically is allowed to turn down gain more than on 144 MHz. Table 2 shows the peak splatter level in 2.4 kHz bandwidth in dB below the peak power in 2.4 kHz bandwidth.


                                        Splatter level below PEP at      
 Model                        Band   5kHz 10kHz 15kHz 20kHz 30kHz 40kHz 50kHz  
                              (MHz)  (dB)  (dB)  (dB)  (dB)  (dB)  (dB)  (dB)
FT-726R (3H030740)             144    30    46    55    61    65    71    76
FT-736R (3J740239)             144    38    53    61    67    78    83    85
IC-275E (01744)                144    41    54    62    71    86    90    94
IC-735 (08265)                  14    38    49    63    71    88    88    88
TS-700 (3020029)               144    29    40    51    54    62    67    70
Table 2. Peak splatter level in dB below peak power at different frequency separations from a SSB voice signal. For details, look at the spectra.


Spectral purity of keyed CW transmissions.

Commercial amateur radio transceivers often have poor keying. The reason is often that the ALC distorts the waveform but other inadequacies are also common. Spectra and in most cases time domain functions (amplitude and frequency) were recorded for these units:

FT-100D 144 MHz
FT-726R 144 MHz
IC-275E 144 MHz
IC-290E 144 MHz
IC-735 14 MHz
R2-CW 144 MHz
TS-700 144 MHz

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. 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
FT-100D (1H240100)             144    53    69    73    75    78    80    82
FT-726R (3H030740)             144    30    40    42    49    54    59    63
FT-736R (3J740239) uppwards    144    60    69    81    87    92    93    94
FT-736R (3J740239) downwards   144    53    55    66     -    -      -    - 
IC-290 (02881)                 144    37    43    47    50    55    60    65
IC-735 (08265)                  14    60    75    78    79    83    83    83
R2-CW (223)                    144    63    65    70    75    78    79    82
TS-700,mod (161193)            144    65    72    76    78    83    88    89
Table 3. Peak power in 2.4 kHz bandwidth in dB below the carrier for keyed transmitters. For details, see the spectrum graphs.


A similar table from the previous Scandinavian VHF meeting Scandinavian VHF 2004 shows equally discouraging results for the FT-726R. That unit was modified but the result this year shows that the reason for the unacceptable result was not in the modification. The FT-726R definitely suffers from some kind of design error. The IC-290 also suffers from unacceptable keying clicks.

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