Diversity Reception

FT-1000D Diversity: Why DX In 'Stereo'? 

by David Sinclair, K3KY


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. 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. 

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 ear using
the sub-rx with 600Hz cw filter and I put the transmit antenna in my
right ear using the main rx with 500Hz or 250Hz filter. (If necessary, I
can crank in even more audio selectivity using my 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. 



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 [2] (CQ Feb 97 p32), which activates a
shorting relay.