The transceiver that you can see in the photo is the result of numerous workhours of Pierluigi (I6WJB) and myself (I6YPK). It has been built in two specimens. It is running since several years in our stations and has given us big satisfactions.
The project of the complete RF part is made by Pierluigi while I was occupied on the digital part (micro,DDS and part of PLL)
I6WJB has a long experience on the building of receivers and transmitters for all frequencies, but we have had the idea to build a RTX at three conversions like this one (the first UP Conversion) thanks to the availability of some professional 8 poles - 70 MHz Crystal Filters. Unfortunately, these filters are not easy available.
mechanical filters at 48 KHz have been recovered on the surplus as well.
They are a little wide (about 3 KHz) than the standard filters for SSB of 2,4
KHz since they are for telephonic use, but they have very steep sides and are
almost free of charge!!
Hereafter you can see the block diagram of the main
characteristics of the RTX HF1. Of course, the characteristics of the RF part
are very important but the digital part as well.
Therefore, the presence of the microprocessor allows to do all those operations that are usually not possible on an RTX with analogic VFO, and therefore I have included a lot of commands like: double VFO, RIT, memories, possibility to operate SPLIT, bottom CW, ecc.
1 Hz Step Frequency Synthesizer
The Frequency Synthesizer is a combination of DDS (AD7008 Analog Devices) and PLL
Wide Dynamic Range
The receiver employs double balanced diode mixer (designed by I6WJB)
Via RS232 Computer interface
Tx - Rx Frequency:
100 KHz ~ 30 MHz
Emission modes : USB, LSB, CW, AFSK, (AM only in Rx mode)
Tuning steps : 1 / 10 / 100 / 1000 Hz
Antenna impedance: 50 ohms
Supply voltage: 13,5 VDC
L.O. Phase Noise : -90 dBc at 1 KHz
Intermediate frequencies: 70 MHz crystal filter (15 KHz bandwidths)
2,5 MHz crystal Filter
48 KHz mechanical filter
Sensitivity (14 MHz) : SSB (3,1 KHz bandwidths) 0,7 uV x 12 dB S/N (pre off)
SSB (3,1 KHz bandwidths) 0,4 uV x 12 dB S/N (pre ON)
Noise Figure: 13 dB PRE-OFF / 8 dB PRE-ON
AGC control: Less than 3 dB rise in audio output for 120 dB signal increase from noise
Audio power : 3 watts into 8 ohms
Spurious Rejection : > 70 dB
3rd Order Intercept Pt. : + 25 dBm
Dynamic range : 120 dB (RF pre-amp OFF)
70 MHz crystal filter (same of RX)
2,5 MHz crystal Filter (same of RX)
Output Power : SSB / CW adjustable 10 Watts (class A) into 50 ohms
Spurious, Harmonics : at least 50 dB below peak output
SSB carrier suppression : at least 40 dB below peak output
HF1_BLOC.DWG (Circad 98 )
Some photos :
Top view "Low Resolution" 39K" o "High Resolution" 117K"
Bottom view "Low resolution" 50K" o "High Resolution" 138K"
First Mixer + 70 MHz Crystal Filter (53K)
Rear View (20K)