The Full Review of the Patcomm PC-500 Transceiver
For the ARS Lab
The PC-500 was such a poor performer on 40 meters that we decided not to include the 40 meter results. Both of our sample radios suggested that something is fundamentally wrong with the 40 meter circuitry (as evidenced by low transmitter output, high spurious emissions, and low receiver sensitivity). We can only hope that our samples were not typical, or that Patcomm will fix what is broken.
20 meters was problematic but manageable. Once again, we encountered poor receiver sensitivity, but with the preamp switched on, the sensitivity was plausible. We ran all of our tests with the preamp on, because we felt that most owners would leave it switched on most of the time. Our comparative graphs are a little confusing, because we were compelled to report the results in the "preamp off" column. Just remember that the preamp was in fact switched on.
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Transmitter Tests
Power Output
With a 12 volt power supply, our sample produced an output of 11.5 watts on 20 meters. Specified full power is 15 watts.
Power Requirements on Transmit
With a 12 volt power supply, our PC-500 drew 3.8 amps on 20 meters.
Spectral Purity
FCC regulations require the spurious emissions from a 5 watt radio to be at least 40 dB below the carrier. For a radio running less than 5 watts, the regulations require the spurious emissions to be at least 30 dB below the carrier.
Our sample had significant problems with spectral purity. At full power, the fifth harmonic was close to the legal limit. At five, watts, a non-harmonic spur was above the legal limit. At one watt, the same spur was too close to call.
Here is are links to the 20 meter spectral purity graphs for our sample.
Keying
The PC-500 had an adequate keying waveform, as shown on this oscilloscope trace.
Introduction to Receiver Tests
Many of our receiver test reports use bar charts that compare the unit being reviewed to a number of other HF transceivers. Please read this brief explanation of the purpose and layout of these charts.
Receiver Tests—When No External Signals are Present
Spurious Signals
On 20 meters, we counted 7 birdies. In addition, both samples we examined had problems with synthesizer noise while they were being tuned. Tuning these radios produced a hiss, which was strong enough to overcome weak signals on a quiet band.
Power Requirements on Receive
Our sample drew 700 mA on receive with a 12.0 volt power supply.
Receiver Tests—When One External Signal is Present
Minimum Discernible Signal
On 20 meters we measured an MDS of -111 dBm with the preamp off, and -123 dBm with the preamp on, in a bandwidth of 580 Hz. As mentioned above, we ran our tests with the preamp on. Please follow this link for comparisons with the MDS of other HF radios.
Phase Noise
We measured phase noise of -128 dBc/Hz at a spacing of 10 kHz from the carrier. Please follow this link for comparisons with the phase noise of other HF radios.
IF Rejection
Our sample's IF rejection was 62 dB. Please follow this link for comparisons with the IF rejection of other HF radios.
Image Rejection
Our PC-500's image rejection was 46 dB. Please follow this link for comparisons with the image rejection of other HF radios.
Spurs
When we test a radio with a DDS, we run a spur test. These spurs are peculiar animals, because their strength and quantity randomly depend on the frequency to which the DDS is tuned. Spurs are an important source of interference.
In our test, we place a strong signal on 14.030 MHz and tune the receiver from 14.0 to 14.060 MHz. The PC-500 had 32 spurs. Although we haven't yet found a more sophisticated way to quantify DDS spurs, based on our testing experience, we would say that this was a meaningful drawback to the PC-500.
Receiver Tests—When Multiple Signals are Present
Selectivity
The PC-500 has a continuously variable filter. At a "9 o'clock" setting, the radio had a combined IF/AF response of 580 Hz. This is the setting we used for many of our tests. Overall, the filter had poor shape, stopband, and alignment characteristics. See the article in the February, 2001 issue of The ARS Sojourner explaining these issues.
You will find interesting information about the width, shape and alignment of the PC-500s IF and RF response in this AF spectrum analyzer graph.
Blocking Dynamic Range
Our sample had a blocking dynamic range of 107 dB. Please follow this link for comparisons with the blocking dynamic range of other HF radios.
In-band IMD
The PC-500 had a poor response to the in-band IMD test. Here is the link to the radio's AF spectrum analyzer graph.
Two Tone Intermodulation Distortion Tests
These tests put us in a quandary. When a receiver's sensitivity is attenuated, the intercept points actually improve. Thus, a receiver can be a dog with respect to sensitivity, but look like a hero with respect to intercept points. Our Receiver Factor test attempts to deal with this tradeoff, but in an extreme case of poor sensitivity (like the PC-500), we sometimes feel that it is better not to publish the intercept point data at all.
In the case of the PC-500, there was a second reason not to publish intercept points. Out sample was not "well behaved." (See Hayward, "Introduction to Radio Frequency Design," page 353, for an explanation of this issue.)
Thus, we decided to not to publish intercept points for the PC-500. Because our receiver factor test depends on intercept points, we could not to publish it either. But we have published IMD dynamic ranges.
Third Order IMD Dynamic Range: 88 dB. Our sample had good third order dynamic range performance. Please follow this link for comparisons with the Third Order Dynamic Range of other HF radios.
Second Order IMD Dynamic Range: 104 dBm. Our sample had good second order IMD dynamic range performance. Please follow this link for comparisons with the Second Order Dynamic Range of other HF radios.
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