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
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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.
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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.
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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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