Dear friends,
After all my "issues" and self-induced catastrophes with the Developer's Edition, which I have working and can now use routinely for QSOs (just got off a voice net using a vacuum tube amp also) -- I was able to pick up Serial No. 141 V2 from a very nice gentleman who had never transmitted over it, and was selling it at a VERY attractive price without a RP4 -- and I had a spare!? ?It arrived in excellent shape and I was very impressed at the cabling and other materials of instruction manual and the case.? ?Everything was very impressive.
Before I commenced to add some of the "further" modifications (aluminum nitride insulators, protective zeners to the final MOSFET gates) -- I wanted to make careful measurements of its performance "out of the box."? ?To avoid losing the whole rig, I added a "polarity protector" out of p-channel enhancement mosfets (4 in parallel,? single digit milliohms of series resistance) that we have a lot of experience with locally.? ? ?I have the same thing now on my DE version.
I created a testing suite in my "ham radio nook" and made measurements.? ?In the course of that, I also made a study of an ICOM 718 as a confirmation of my testing suite.? The ICOM 718 is a workhorse analog transceiver which has had multiple versions of the final amplifier under the same model no.? ?There have been bipolar as well as MOSFET final amps.? ?I believe mine is MOSFET but I haven't taken it apart in so many years I don't know for sure; it has been WINLINK RMS KX4Z for > 4 years, running 24/7/365 on HF, rain, shine, hurricane, whatever.? ??
The testing suite involves:
1. MFJ switching power supply with added powerpole leads
2. Transceiver under test
3. Short coaxial cable to an ancient Radio Shack combined SWR meter/"wattmeter"? (this is essentially an RF voltmeter calibrated for 50 ohms)
4. Short coaxial cable to an ancient Heathkit Cantenna 50 ohm 1kW oil-immersed dummy load, modified to have a resistive (non-compensated) attenuator to a BNC output
5. Short double shielded BNC jumper cable to a 6dB pad to a Siglent SSA3021X spectrum analyser.
The Heathkit homemade attenuator is NOT compensated.? ?Using the Siglent tracking generator I was able to calibrate the response of the attenuator using exactly the same cabling to the RF input of the Siglent.? ? REFERENCED TO THE 3.5 MHZ SIGNAL here are the observed outputs, showing that more signal gets through at higher frequencies:
3.5 MHz? ?(reference)
7 MHz? ?+1.5 dB
14 MHz? + 4 dB
21 MHz? ?+ 6 dB
28 MHz + 8 dB
42 MHz? + 11 dB
56 MHz + 13 dB
63 MHz? + 14 dB
84 MHz? +16 dB
All of the power measurements reported here will be CORRECTED for these offsets where the attenuator passes MORE SIGNAL for higher frequencies (e.g. for harmonics)
The testing scenario was the same for all radios.? ?The only differences were changing the frequency range of the spectrum analyzer, and which bands were tested.? ?Siglent spectrum analzyer set to 10kHz receiver and visual bandwidth (this is fairly narrow and slower, but gives good sensitivity)
CW approximately 10kHz above the bottom of each band was used.? ?The Siglent has a mode where it picks up "peaks" and reports their frequenciy and power level.? ?From those "dBm" measurements, one can then use subtraction from the carrier signal to come up with referenced "dBc"? (dBcarrier - referenced to the desired signal) numbers.? ?For our HF rigs below 30 MHz, spurious responses generally must be -43dBc or weaker.? ?THere are other regs above 30MHz but I haven't reviewed them.
HERE ARE THE REFERENCE RESULTS FOR A VERY OLD ICOM 718
Power level set to "50%"? ?Power measurements below are APPROXIMATE on the highly questionable Radio Shack SWR/power meter intended for CB operators
MHz? ? ? ? Fundamental? ? ? ? ?Any notable Spurs? ? ? ? 2nd harmonic? ? ? ? ? ? ? ? ? ? ? ? ? ?3rd Harmonic
3.510? ? ? 39Watts -18dBm? ? ? ? ?Below -73dBm? ? ? ? ?NONE SEEN above noise? ? ? ?10.5 MHz? -78 dBm? ?-60dBc
7.01? ? ? ? 25Watts? ?-19dBm? ? ? Basically none? ? ? ? ? ?NONE SEEN above noise? ? ? ? 21 MHz? ?-77 dBm? ? -58 dBc
14.010? ? 25 Watts? -18.85dBm? 5.6MHz? -66dBm -47dBC? NONE VISIBLE? ? ? ? ? ? ? ?42 MHz? ? -80 dBm? ? ?=61 dBc
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?16.8 MHz -71dBm -52dBC
COMMENTS:
1.? ?The testing setup appears validated.? ? The results indicate that the ICOM 718 well-worn transceiver has very very little 2nd harmonic, suggesting the push-pull amplifier is very well balanced, and the 3rd harmonic is very well suppressed
2.? ?The Icom does have a couple of notable spurs on its 20 meter band but they are well below the FCC regulation specification.
Here is a photograph of the testing setup:
In the next post(s) I'll provide testing results with the V2 sBits that I received, as received (with Raspberry pi installed)
Gordon L. Gibby KX4Z
