I/O Services Sidecar for the Z3801A
this article Daniel Nelson describes the design of his
I/O Services accessory box that attaches sidecar style
to the rear of the Z3801A.
began my adventure with the Z3801A via an Ebay purchase
giving me the box and Magellan puck antenna with free
shipping. The purpose of the purchase was to provide
a self-calibrating 10MHz clock signal for various test
equipment on my bench. From this need, I have developed
the Z3801A GPS Interface detailed below. I hope it may
help you with your project. Feel free to use any of
the information and please contact me with your observations
and questions at firstname.lastname@example.org for Daniel Nelson.
GPS Interface project requirements:
Do NOT modify the Z3801A - everything MUST be added
as a 'sidecar' that bolts onto the existing unit.
- Isolated 10MHz sine wave outputs to simultaneously
feed several test instruments on my bench. Spare outputs
must be available for future use.
- 120VAC to 48VDC Power supply for the Z3801A
- RS-422 to RS-232 conversion to hook up my computer
- F antenna connector for easy use of commercial cabling
- TTL 1PPS outputs with 50% duty cycle to drive 50 ohms
- TTL 10MHz 50 Ohm square wave output - just in case
block diagram below shows the circuits to convert the
Z3801A outputs to my circuits. After reading the various
web pages and sites and looking over the available parts,
the following strategy was conceived:
aluminum chassis can be bolted onto the rear of the
Z3801A using the existing mounting nuts and bolt holes.
Attachment of my unit to the receiver was found to
be tough enough without adding any new holes.
metal chassis is available for purchase that is the
same size as the rear of the Z3801A. I settled on
a 3" tall, 10" wide Bud box. This is slightly
shorter and several inches wider than the receiver,
however, it is not as wide as the front rack flange
and so will allow insertion into a cavity built to
accommodate the original unit (depth of the new box
supplies would be needed to run the Z3801A and the
Z3801A - 54V @600mA max
+ 5 and - 5 @ 250mA for Maxim distribution amps
+ 5 for other circuits
A Cincon 48V 60W switcher offered by Mouser has enough
excess current to supply both the Z3801A and the other
needs. So I configured the power system by converting
120VAC to 48VDC (adjustable to 54VDC) and then using
DC-DC converters to make the +-5 and +5 supplies from
sine wave outputs take advantage of the article by
DL8JT "10MHz Video
Distribution" by Wolfgang Sauerwein on this
site. In this he details use of a Maxim 4135 Evaluation
Kit to make 6 independent outputs. A truly wonderful
observation was that 1:1 isolation transformers are
available on obsolete network cards, along with the
isolated BNC connectors. The combination of the Maxim
board, transformers and connectors satisfy the isolated
4135 Evaluation Kits:
on two of these for a total of 12 outputs. Later, I noted
that one would have been enough, but there it was, sitting
there, money spent, so I went ahead and put both into the
'sidecar'. These are available for direct purchase from
the MAXIMIC.COM website.
box is exactly 3" tall - outside. The MAXIM boards
are exactly 3" tall so they had to be sanded .030"
on the top and bottom edges to remove enough to fit inside
the chassis. Tedious work with a file, but worked out
Z3801A has ONE 50 ohm output at 10MHz. In order to have
as much amplitude as possible and to feed both the MAXIM
units, I decided to modify the MAXIM boards. I removed
R7 a 75-ohm surface mount resistor and replaced it with
a 1/8 watt 100 ohm resistor (done after photo taken).
Two boards in parallel then presents 50 ohms load to
the Z3801A +- reflections due to split feeds to the
2 MAXIM boards. Works fine.
removed the DIP-switch from the MAXIM kit as it ended
up in a poor place in my construction. Besides, I intend
to run all the outputs all the time and not try to use
the DIP-switch at all. After removal, the contacts on
the board were jumpered so all six outputs are enabled.
The MAXIM Kits require both +5 and -5 supplies. By my
calculations, two of the kits will work fine when supplied
by a single 300mA source.
have inserted 2-pin male headers into the MAXIM board
for +5, -5 and ground to allow plugging the supply harness
into them after assembly. These boards are well bypassed
and so the power supply wire lengths inside the 'sidecar'
are not at issue.
MAXIM kits have 1 + 6 SMA connectors for the input and
6 outputs. I was able to purchase about (20) 6"
SMA M-M cables on Ebay to use for interconnects between
the kits and the output board. See the photo for details.
Wiring was straightforward. Each completed group is
bolted to the rear of the 'sidecar' using the BNC connector
noted in the DL8JT article, isolated outputs are needed
for each of the 10MHz sine wave connections. Cables
that connect equipment to the distribution amplifier
must not, at the same time, connect the equipment to
each other. Coax connections of perhaps several feet
can produce different 'ground' potentials across the
suggested, I was able to obtain about 20 old network
cards on Ebay for under $25, delivered. From these I
scavenged the isolated BNC connectors and the 1:1 isolation
transformers. With these each output is isolated from
all others and not referenced to ground at the distribution
mounted the isolated BNC connectors 3 in a row to a
strip of breadboard, connected the 1:1 transformers
and the end of the SMA cables. Two of these breadboards
and SMA cables connect to the modified MAXIM kit to
comprise a package of 6 isolated outputs.
Preparation and Stuff !
first thing was to put the holes into the box. I created
a drawing for the rear label and sent it off for manufacture.
This label was used to mark the hole centers after sticking
it to the box wall. The hole for the power entrance
was actually cut with an X-ACTO saw blade and then filed
to final size. The other side was drilled for attachment
to the Z3801A. Finally, the power supply was mounted
on one end.
single breadboard was created to mount most of the remaining
parts. It has both the +5/-5 and +5 DC-DC converters
on it, RS-422 to RS-232 and pseudo-ECL converters. I
put a number of .1" male headers on the board for
connections. Details are below.
the antenna, a cable with an N connector on it was cut
off and then soldered the F jack mounted to the rear.
For the computer, a DB-9 female connector was pre-wired
bolted to the rear wall. I also pre-wired a DB-25 male
connector with the wires for the RS-422 , 1PPS and 10MHz
outputs. Wiring was routed to the breadboard card.
found a led in a chassis mount package with dropping
resistor rated for 12 volts. This was wired across the
+ and - 5V supply. The 120V entrance was wired and grounded
at one of the mounting bolts holding the 'sidecar' to
the Z3801. All else is on the breadboard.
Card - Conversion Circuits:
This card is the core of the project. Here I mounted
circuits for power supplies, pseudo-ECL conversion,
RS-422 to RS-232 and conditioning for 50 ohm outputs.
I will treat each separately. DC-DC CONVERTERS: The
Maxim distribution amplifiers, loaded to 50 ohms and
driven with 1.8Vpp inputs from the Z3801A are slated
to draw a total of 250 mA from both a +5 and -5 volt
supply. I picked out a DC-DC converter from Mouser,
418-EC3A34H made by Cincon. This is a 3 watt converter
and provides regulated +-5V @ 300mA from a 32-72 VDC
supply. Obviously it is tied to the 48V DC supply.
I was concerned that the +5 supply would be overloaded
when the 1PPS and 10MHz TTL outputs were loaded to 50
ohms. Over this, I have added a second DC-DC converter,
also from Mouser, Cincon 418-EC3A31H. Probably one dual
voltage DC-DC converter above will work fine, especially
if only one Maxim kit with 6 outputs is used. Again,
the stuff was purchased, sitting here, so I put it in.
used the schematic right off this website for this using
the Max232 and SN75179BP chips. For clarification, I
have shown the again schematic below. Note that ground
on the DB-9 connector is power supply ground.
to 10MHz TTL Output:
studying several articles on the definition of Pseudo-ECL,
the following working understanding was reached:
review: ECL uses a -5.2VDC supply with open emitters
that are terminated in maybe 50-100 ohms at the far
end of the signal path. Signals were below zero with
logic 1 at -.9V and logic 0 at -1.8V.
is the same as the above but uses a +5V supply, so the
signal levels are positive with logic 1 at +4.0V and
logic 0 at +3.3V approx. What is of interest here is
that the Z3801A signals are differential and fed with
two wires. As it turns out, these signals are well inside
the voltage levels for RS-485 transmissions. The differential
swing is high enough to be compatible also. I employed
a 75176B RS-485 chip to convert the Z3801A signals to
TTL. This is a single chip solution that in addition
has the drive ability to drive a 50-ohm output directly.
520 ohm loading resistors were picked for low power
to terminate the incoming differential lines. A 520-ohm
resistor loads the 75176B output to kill ringing and
maximize signal quality.
used the 75176B RS-485 receiver section as noted above
to translate the 1PPS signal to TTL levels. The 1PPS
signal is a narrow positive going pulse. So, to provide
a 50% duty cycle, I used an NE-555 timer to generate
a 50% duty cycle square wave. The NE-555 has enough
current capability to drive a 50 ohm load directly.
The NE-555 is triggered by the rising 1PPS pulse and
then generates a logic 1 on its output for ½
second. The timer then waits to be triggered on the
next 1PPS rising edge. The ½ second time is defined
by: t=1.1RC. Be sure the actual parts selected for the
RC time constant equal .454. Using a 1M resistor, a
.454 uF cap would be needed. Select a combination of
resistor and capacitor that is close to this value for
a 50% duty cycle.
have enclosed a parts list by functional block. I am
pleased to report that after assembly, all the circuitry
worked fine without adjustments, so I expect that anyone
can breadboard up whatever bits of this project that
seem appropriate. If you have questions or observations,
please feel free to contact me at Daniel Nelson email@example.com.
You are free to use this information for your project,
pass it on to others.
My Z3801A is up and running great! I placed the antenna
on a Radio Shack15-891B eave mount just proud of the
center ridge. As recommended in the literature, I also
installed a Radio Shack 16-1156 In-Line Amplifier to
boost the antenna strength. Currently, I have SS (Signal
Strength) numbers reported in the 75 - 175 range and
no complaints from the system.
I purchased the GPSCON software offered by K8CU and
really like it. This program runs in the background
on my computer logging data and providing me with a
visual picture of how everything is working.
all drawings as high resolution PDF file
Misc and Chassis
1 In-Line Antenna Amplifier Radio Shack 16-1156
1 Adapter BNC-F to F-M To adapt antenna to amplifier
1 Antenna lead-in 75 Ohm RG-6/U Coax with F connectors.
Length as needed.
1 Mount - Antenna - Whatever works for your house!
1 Universal Power Cord
1 DB-9 Serial Cable Connect GPS unit to computer
1 DB-9F Solder Cup
1 DB-25M Solder Cup
1 F-F Bulkhead Connector Solder
1 8" Coax cable N-M one end.
1 Label, GPS Local label maker
1 Box, Aluminum 3 x 5 x 10 Bud AC-404 Mouser 563-AC-404
1 Cover, 5 x 10 Bud BPA-1591 Mouser 563-BPA-1591
1 Plug, 3 pos Amp Mate-N-Lok 1480700 Mouser 571-14807000
For DC to Z3801A
2 Socket Pin, Socket Amp 3506891 Mouser 571-3506891
For (1) 6 output distribution amp
6 6" Coax cable SMA-M one end. Ebay or surplus
1 6" Coax cable SMA-M to BNC-M Ebay or surplus
6 Isolated BNC connector similar to BNC-LNRD-BPNA From
old NIC cards
6 1/2"-28 Nut Mounts BNC connector to chassis
2 Triple 1:1 10MHz Isolation Transformer LanKorn LP-160C
or Bothhand TA100-05B
1 Maxim MAX4135EVKIT-SO Dist Kit - Order from Maxim
12 #2 Lockwasher - used to solder BNC connectors to
2 .062"x1.1"x2.9" Pad Per Hold Breadboard
4 4-40 x 3/8" Hex spacer
8 4-40 x 1/4" screw
For (2) output distribution amps
2 List of items above
2 100 Ohm 1/8W Carbon Film resistor - Change R7 on the
1 BNC Tee
1 48VDC 60W Switcher CinCon CFM60S480 Mouser 418-CFM60S480
1 3 pos housing Molex 09-50-3031 AC Plug
© 2004 Daniel Nelson