FT-1000D Diversity: Why DX In 'Stereo'?
Humans, having two ears, are good at localizing sounds and quickly estimating their direction and distance. Our ear/brain filters work quite naturally in stereo. In the 1950s and 60s, people gladly dumped their monaural hi-fi gear and switched to binaural (stereo) systems because they sounded so much better- yet today most of us still listen to our HF radios in mono. The first time I tried DUAL mode on my FT-1000, I was quite impressed with what I heard.
At that moment, I knew I would be using diversity a lot in future DXing! Diversity reception opens up a whole new world to the DXer- weak and fading signals can be heard better than ever before. Even noisy band reception can sometimes be improved over using low noise receiving antennas alone ('monaural').
My radio has the BPF-1 bandpass filter. Separate antennas connect to the SO-239 jacks for ANT and SUB RX ANT ( to do antenna diversity, this option must be installed). S1001 on the RF board is set to E BPF, and the front panel RX ANT switch is set to ON. (Switch settings and connections may change after I install the K0FF Mod plus fancier external antenna switching) After tuning in a signal with the main rx you can punch A>B and DUAL to enter diversity mode. I have the G3TKF Synchro Mod installed, so I can tune up and down the bands effortlessly in full diversity using only the main tuning knob.
For headphones, the PHONE switch inside the Top Access Panel must be set to st (stereo) to enable diversity in DUAL mode. Otherwise, the AF OUT rear panel jack must be used to drive an external stereo amplifier. (Transmit monitor audio will not be heard in the speakers) I find that I can set the RX MIX at about 12 o'clock and pretty much forget it. The ear/brain filter is very forgiving of large differences in signal strength between channels. (16 Jan 02: I have since discovered that my headphones were miswired with R and L interchanged. My normal RX MIX setting is about 10 to 11 o'clock. I have not yet bothered to figure out whether this gain imbalance is in an RF or audio stage, since the setup works so well as is. I often make slight balance adjustments when changing bands or antenna combinations, or when switching the RX ANT control between single antenna/dual receivers (OFF) and dual antennas/dual receivers (ON). It is a one time, set and forget adjustment for each session.)
A few examples: On 40 and 30 meters, I have high, horizontally polarized antennas- a 2el 40 at 120ft and a WARC triband dipole at 127ft. Their
performance is great, but noise pickup is a big problem, especially in the summer. I therefore use various low noise receive antennas, including a Flag , a K9AY, and an optimum length 'cone of silence' 225ft Beverage. Sometimes the Beverage will bring a Q3 European signal almost buried in noise up to Q5.
So why not listen only on this antenna? I find that polarization diversity adds an equally good improvement. I put the Beverage antenna in my left right ear using the sub-rx with 600Hz cw filter and I put the transmit antenna in my right left ear using the main rx with 500Hz or 250Hz filter. (If necessary, I can crank in more audio selectivity in the Sub channel using my excellent Timewave DSP-599zx) The combination is stunning! Signals take on a 'presence' and clarity that is missing using either antenna/rx combination alone (mono). Sometimes I can hear a signal fade back and forth between the two audio channels as polarization changes. Gaps where the signal would once have taken a deep fade are now largely eliminated. These differences must be heard to be fully appreciated.
On 160 meters I use a full size loop with the apex at about 110ft. On 80 meters I use a full size quarter wave wire vertical with about 55 random length ground radials. For receive antennas I can choose between my Flag, short Beverage, K9AY, and K6STI loop The K6STI is often the best of the bunch at my location. Once again, antenna combinations that pair a low noise rx antenna with my transmit antenna have proven highly effective. In May 2001 I worked PV0F on both 160 and 80 CW. 80 was easy, but I had to struggle to be heard on 160m. I was copying them Q5 nearly all the time. With diversity, I am a bit less of an 'alligator' than I used to be.
On 20 through 10 meters, I use various combinations of transmit antennas to good advantage. Often high and low horizontally polarized antennas
together produce good 'fill', as propagation varies between higher and lower wave angles. A typical pair for 17 meters is my 7el log periodic at 40ft for transmit, teamed with my F12 C4XL at 120ft. As always, the signal sounds 'muddier' in either channel alone, and much clearer and sharper in diversity.
Quite often, Q3 or 4 signals are brought up to Q5. The actual antenna combinations are many, since the optimum pair varies by band, distance, and
changing propagation conditions. A 2 port by n antenna switching matrix, such as the WX0B Array Solutions Six Pack suggested itself early on for this 'stereo' antenna/receiver scenario. A lockout feature is a good idea to prevent the sub-rx from ever sharing an antenna with the main rx on the
transmit side of the FT-1000 relays, thus getting fried by the transmitter. The Six Pack has this important feature.
After many months operating on all HF bands 160 through 10 meters with antenna diversity, I can report that it is well worth the effort to get set up for this great mode. I believe the G3TKF synchro mod is essential. I cannot overemphasize how much of an improvement it is to be able not only to receive in diversity but also to actually tune around on a band in full diversity mode! If you have two antennas* which are both receiving a weak DX signal at least a little above the noise, then the combination of both will usually improve intelligibility on average and will always provide easier listening with much less strain and fatigue. Go for it! (* antennas separated by height or horizontal distance, or of opposite polarity)
Synchro Mod User Tip:
With a dual receiver setup, it is a good idea to install front end protection for the sub-rx to guard against antenna coupling during transmit. One simple method is the KD9SV Front End Saver (CQ Feb 97 p32), which uses fast reed relays to open the feedline and short the receiver input to ground. A blank PC board is available from FAR Circuits. (Scroll down to CQ Feb 97/ KD9SV). Assembled units are also available direct from the designer, Gary Nichols, KD9SV