The component values
are marked on the schematic shown above but a few extra points are
The variable attenuator:
I already had a few of these nice little pc mounting variables in
my junk box. Although they do not provide a constant input and output
impedance (and therefore not a good VSWR for the FT817), they are
very convenient. A fixed resistive attenuator (T or Pi type) can
easily be substituted and calculated from the values of RF input
and output required.
I decided not
to switch out the attenuator when receiving as my transverters have
more than adequate gain in reserve to overcome the 6dB or so of
attenuation in the IF line. This is probably the case for most systems.
This is for polarity reversal protection. Any 12V DC type
will do here so long as the contacts can handle a few amps. I used
one rated at 10A. To reduce overall load on portable batteries choose
one with low coil current.
This is the main control relay. I used a miniature 12VDC type with
1 amp contacts.
With both relays,
dont forget to put 1N4001, or similar diodes, across the coils
to prevent back EMF effects.
A small axial lead 0.33uH type
8 Pin mini-DIN
connector (male: This is needed for connecting the interface
to the ACC socket on the rear of the FT817. Make sure that the inner
of the thin coax lead goes to pin 2 and the shield to pin 3 of the
male connector. Use the pin numbers on the connector itself to absolutely
sure you have the correct pins. Wrap some insulation over nearby
pins, one of which, pin 1, carries +13.8V from the FT817. Short
this to ground at your peril! Refer to the FT817 manual diagram.
On the ACC socket pin 2 is named TX ground and pin 3
ground. Do not us e the PTT pin on the DATA socket.
Sense Switch: A small slider switched was mounted on three pins
that are soldered through the perforated board. Pin 1 of the 7808
regulator is connected to the slider. In the schematic, pins A and
C are connected by the switch to simulate IC202 control switching
while pins C and B provide FT290 type switching.
I used a short length of RG174 here, taking care to minimise the
exposed sections of inner
conductor at the attenuator and the BNC connectors.
The interface worked first time and made a recent contact with a
new local 10GHz station a real pleasure. One added advantage of
using the FT817 is that if KYR is selected by pressing
key F on the front panel, the C function switch below the main dial
puts the FT817 into beacon mode, sending a steady stream of dots
or dashes according to your tastes. After over a decade of using
IC202s to make hundreds of microwave contacts you get quite used
to using antiquated gear. Only now do I feel Im in real control
of frequency setting!
1. Bias Tee for Remote Transverter Control - Paul Wade, W1GHZ:
Microwave Update Proceedings 2002
2. Interface circuits for the FT817 - Dave Robinson, WW2R
Microwave Update Proceedings 2002 and also RSGB Microwave Newsletter
DOWNLOAD COMPLETE CONSTRUCTIONAL
ARTICLE HERE: FT817
interface v 2.pdf