Electro-Metrics EMC-30 EMC Receiver - Page 1
Forum section: electronics / testgear

author: dazz1
author_rank: Frequent Contributor
timestamp: April 26, 2023, 05:51:06 am
content: HiI have just collected an Electro-Metrics EMC-30 EMC test receiver.It is the MkIV version build mid 1988. It came complete with custom transport case and the Instruction manual with circuit diagrams.The manual for the analysis software is also there, but the printer port dongle and the software itself wasn't. Also not included are any accessories, antenna etc.Designed and built at a time when technology was measured in kilograms, in its traveling case, the radio weighs 38kg so definitely a beast.Despite its age, the radio is in very good condition. Just minor blemishes.Prior to applying power, I opened up the radio to do a static power-off inspection to look for obvious failures. I didn't see any because I couldn't. Most of the circuits are housed in shielded metal enclosures. No short cuts taken here. I particularly wanted to inspect the power supply but it was in a welded enclosure that looked difficult to get into.A sign of the times was the label identifying the RF Tuner Gear change, for switching across the bands.The receiver has features of hand-made, low volume production mixed with high quality build techniques. The modules are all mounted and enclosed in a very military way but there was also a little wire-wrap and kludge soldered link wires.When power was applied, all of the magic smoke remained trapped inside the radio. All of the knobs, LEDs and indicators worked. As far as I can tell, the receiver is fully functional. I need to hook up my scope and RF sig-gen to do a basic calibration.At present, I am soak testing. It has probably been years since the receiver last felt the warmth of electron flowing.Although the radio is obsolete and only receives to 1GHz, it can be used for EMC pre-compliance testing. To do that it really needs to be operated via the GPIB so I need to buy/build a GPIB/USB adapter. I can buy a electronically controlled antenna switch from Aliexpress.

author: dazz1
author_rank: Frequent Contributor
timestamp: June 18, 2023, 04:22:30 am
content: HiThe EMC-30 has a connector on the rear to control a 6-way antenna selector. The antenna selector can only be controlled via the GPIB command set, so I need a USB-GPIB adapter (still waiting for the PCBs).I don't have the Electro-Metrics antenna selector, so I have decided to make one. You may be wondering I would need a 6-way antenna selector. That's easy to answer. If I didn't make an antenna selector, I wouldn't need the GPIB adapters.I do have 2x wide band PCB antennas plus the biconic one I am making.The receiver can control 2x antenna selectors to select one of 12 antenna. I could make a second antenna selector, but what would be the use of that.The first task has been to make the connector assembly. I purchased a new Amphenol mating connector from e-bay, and then purchased some Mil-Std type connectors off Aliexpress. The Chinese ones look like the real thing.Unfortunately the rear panel connector is a small 19pin Mil-Std connector. Usually mil-Std connectors include options to fit a back-shell that allows for a reasonable length of removed sheaf. Not this one. Very difficult to strip the insulation and solder the cores.I had to make a custom 3D printed wire insulation stripper to be able to keep the wire ends as short as possible. I also printed off a clamp to hold the connector while I was soldering the wires. I soldered the wire cores to the nearest pin, without regard for cable numbers. No room to cross cores.The Chinese connectors were larger and allowed for a longer length of un-sheaved cores. Much easier to solder. To make sure I got the wiring done right, I beeped out the cores.

author: dazz1
author_rank: Frequent Contributor
timestamp: June 18, 2023, 04:25:10 am
content: HiHere are pictures of the Chinese connector and the finished cable assembly.The Chinese connectors are made to MIL STD 5015, and they look good. It is possible they have come from the same factory that makes certified connectors. They are good enough for me.

author: dazz1
author_rank: Frequent Contributor
timestamp: June 24, 2023, 09:30:16 am
content: HiI need an enclosure for my 6-way RF switch controlled by the EMC-30 receiver. I wanted to choose one from Aliexpress, because having one sent from China is cheaper that buying one locally.I picked a box and draw up a quick CAD drawing to check sizes and spacings.I have shown two Chinese clone Mil-Std 5015 connectors, but I will only fit one. The second connector allows for the control of another identical 6-way RF switch to select one of 12 antennas. There is little danger of my owning 12 antennas to switch.Locating the connectors on all 4 sides is far from ideal, but this is the only RF compatible diecast enclosure that is deep enough for the Mil-Std connectors.The EMC-30 receiver goes up to 1GHz, so I could use BNC connectors, but they don't look like ruggedized military stuff, so I am going to use N-type. As an added bonus, the Chinese N-types should at least perform to 1GHz.

author: dazz1
author_rank: Frequent Contributor
timestamp: July 12, 2023, 11:21:19 pm
content: I have started making the antenna selector switch. It is based on an Aliexpress module fitted with an Analog Devices HMC252.I need to build a circuit to interface the antenna control signals from the EMC-30 receiver. Plan A was to build the interface with wire wrap and then test antenna selection with the receiver. I could easily make any changes to the wire wrapped circuit to correct bad assumptions or other errors.I would need to buy additional wire wrap IC sockets and the cost of these will exceed the cost of a custom made PCB. I have now decided to do a pcb. That requires a different approach because I don't want to be correcting pcb errors.First off, I need to check exactly what control signals are coming from the EMC-30 receiver. The tech manual has limited info. The control signals are driven by the EMC-30 microprocessor, so I need to identify the protocol before I commit to getting a pcb made.

author: dazz1
author_rank: Frequent Contributor
timestamp: August 28, 2023, 11:59:14 pm
content: HiProgress on the Ax switching unit has been slow but progressing.I had the enclosure powder coated genuine New Zealand Army green (AKAA cow poo green) because I want the unit to look military. I like things I make to look like they came out of a factory.The RF switching pcb won't fit laid horizontal so I printed a 3D bracket to hold it. This uses screws on the RF connectors to hold the bracket in place. No more holes in the enclosure.The next stage is to make a prototype switch controller to interface the Electro-Metrics EMC-30 control signals to the RF switch. Before I can do that, I need to build the USB-GPIB adapter and then learn Python to write the code to control the Electro-Metrics receiver.I have attached the schematic of the RF switch controller. This is designed with old school TTL logic devices because they don't need a clock signal. I didn't want to deal with EMI generated inside the enclosure.The EMC-30 is able to control two RF switching units via the single control cable. The adapter is designed to allow two RF switching units to be daisy chained. This would allow selection of any one of 12 antenna. I currently have no intention or need to switch that many antenna, but it won't cost me any more to make a controller that has that capability.It is going to be a while before I post another update on this project.

author: dazz1
author_rank: Frequent Contributor
timestamp: March 04, 2024, 07:24:22 am
content: HiThe other day I turned on the EMC-30. It hummed and the magic smoke escaped from the power supply.The EMC-30 way too complicated. The interconnect diagram attached shows the connections between different parts of the receiver. The attached diagram is high-lighted to trace the power flow throughout the receiver.I traced the fault to the microprocessor card. Getting access to the card to find the faulty component required extensive disassembly.The only visible indication of the faulty Tantalum capacitor was a slight discolouration. If I hadn't had the circuit diagrams, it would have taken ages to find the fault.Rather than trying to change other tant caps in anticipation of them failing, I added two fuses on the secondary of the transformer (see photo) to provide a slight improvement in fault discrimination. A lot easier than trying to replace every tant cap.While opened up, a survey of the chips showed some pcbs had been manufactured in 1983 but the firmware PROM date is Nov 1991. Parts of the receiver were already old when the receiver was new.

author: dazz1
author_rank: Frequent Contributor
timestamp: March 04, 2024, 07:36:15 am
content: HiWhile I had the EMC-30 open, I decided to add lighting to the analog signal meter. It is quite dark and not easy to read.I added a cut-off strip of LEDs to the top of the meter. The photo exaggerates the brightness of the centre part of the illumination and shows how dull LEDs were in the 1980s. It looks fine in real life.A lot easier to see, and better looking with a light.

author: tautech
author_rank: Super Contributor
timestamp: March 04, 2024, 08:28:05 am
content: Tants are Murphy's foot soldiers !Kill them all with extreme prejudice unless 50% overrated for the rail they are on.

author: dazz1
author_rank: Frequent Contributor
timestamp: March 04, 2024, 08:48:48 am
content: HiI priced replacing all of the tants on the WaveTek 2520. The tants would have cost more than the WaveTek is worth.The EMC-30 is even more complex that the WaveTek 2520. It would take weeks and even more $$$ to replace all of the tants in the EMC-30.Both the EMC-30 and the WaveTek look like they have been designed by committee. You can definitely see the signature style of the designers of each section.On the outside the EMC-30 has Mil-Spec connectors. On the inside it is full of non-polar headers without retainers, especially for power. If those power headers are offset, or turned around, the electronics would be fried. These EMC-30 receivers were hideously expensive when new. Even old used Electro-Metrics gear on e-bay is still expensive.I rather suspect that EMC-30 receivers end up in the skip bin because they would be very difficult to repair without the schematics that I have. That is apart from the EMC-30 being obsolete with a range of only 1GHz. Still useful for pre-testing.

author: dazz1
author_rank: Frequent Contributor
timestamp: March 05, 2024, 04:20:42 am
content: HiThese two manuals for the EMC-30 receiver and related PC (DOS) software are rare. There is a bad photocopy of the Ops section manual on e-bay but I don't see the service section. There is one EMC-30 receiver with ops/service manual on e-bay for $AUD1200, which is quite expensive for a 30+ year old obsolete equipment.I am not sure that the service manual was standard issue. I suspect the service manual may have been an overly expensive option to encourage customers to return the receiver for factory cal/servicing.I don't have the software or the printer port dongle that was necessary to run the software. It is a useful guide to writing modern gpib software to control the EMC-30.Does anyone else have one of these receivers?

author: dazz1
author_rank: Frequent Contributor
timestamp: November 25, 2024, 08:10:16 am
content: HiOnly about 1 1/2 years to finish this project for the Electro Metrics EMC-30 EMC receiver. This project is an antenna selector unit (ASU). This allows 6 or 12 antenna to be selected over the GPIB interface. One ASU can select up to 6 antenna. Two ASU's can be daisy chained to switch up to 12 antenna. I needed to get the usb-gpib adapter operating first before I could test the ASU.Unlike the original Electro-Metrics version, this ASU features:LEDs to indicate which ports are active,Genuine New Zealand Army poo green camouflage powder coating, just in case,A cheap Chinese electronic antenna switch moduleI went down the risky path of designing and ordering the pcb without first bread boarding a prototype. Even so, the ASU works.Not quite sure why I need to switch 6 antenna but it certainly justified the usb-gpib adapters, which I needed to control the ASU.Only thing left to do is measure the performance of the electronic switch module.Now I just need to keep working through the long list of other unfinished projects.

author: dazz1
author_rank: Frequent Contributor
timestamp: November 25, 2024, 07:04:50 pm
content: For comparison, here is the Electro Metrics ASU-136 I have only just looked for and found.The one feature on the ASU-136 that is not on mine is manual selector switches. Adding those to mine would have required a lot of metal work and internal wiring. I made the hardware to avoid any screw heads in the die cast enclosure. The only external screws are for the connectors. I custom designed 3D printed brackets to hold the internals in-place.I based my ASU on the EMC-30 receiver GPIB instruction set. The instruction set is configured for 2x SP6T. The EMC-30 rear panel connector is configured to daisy chain 2x ASUs. That is how I designed and built my ASU. I didn't fit the 2nd connector on the enclosure.The ASU-136 looks like it is 2x SP2T in one enclosure [or it could be 4 inputs to 1 of 2 outputs]. It has two outputs, but the EMC-30 receiver only has one rf input. So not sure how that would work with the EMC-30 Rxr.The motive for building the ASU was that I expected to connect at least three antenna to test emissions up to 1GHz. Commercial biconics have a range out to about 300MHz. That was before I designed/built my biconic antenna with a frequency range out to 1GHz. There is still room for a low frequency range antenna to compliment the Biconic. Rather than switching/selecting 1 of 3/4 antenna as originally intended, I may only end up with 2 antenna.Of course the time/effort/cost of building the ASU will always be far greater than the time required to manually swap antenna during tests, but where is the fun in that.

author: dazz1
author_rank: Frequent Contributor
timestamp: November 29, 2024, 07:33:14 am
content: OK I have measured the frequency response of SP6T RF switch.Here are the results.I only want to use the rf switch out to 1GHz, the max frequency of the EMC-30 Rxr but the plots are out to 3.2GHz.The input and output of the switch had 10dB attenuators fitted to eliminate cable and mis-match reflections. I didn't measure SWR. Maybe another time.The measured results show a reasonably close match in frequency response from one channel to the next. This is important to me because I can use any channel without needing to calibrate for a particular channel.The isolation between an off-channel and one that is not, is reasonable. Not lab standard but certainly workable for my application.The measured frequency response of just one channel, Ch1, is reasonably flat.Given that the rf switch from China costs less that a Chinese take-away dinner from the local shop, the performance is good enough. Possibly better than a hardware based rf switch.Any inadequacy in the performance is compensated for by the appearance of the LEDs and the nice big MIL-SPEC connectors. Even if it doesn't perform to the highest specs, it looks like it should cost many $$$. It is a close partner to the Electro-Metrics receiver, which also has MIL-SPEC connectors on the outside, and a lot of cheap, but expensive, dodgy engineering on the inside.If I leave my new rf antenna selector unit on the coffee table, I can bore my friends to tears after they foolishly ask "What is that?"

author: dazz1
author_rank: Frequent Contributor
timestamp: January 17, 2025, 03:03:41 am
content: HiI have been working towards getting the EMC30 operating via the GPIB.The EMC30 had the option of software for remote operation. It came to me without the software or the centronic printer port dongle (anti-pirate device). The company that wrote the software also wrote the EMC30 firmware. It makes sense that they would ensure the GPIB commands worked properly to make it easier to write the GPIB software that ran on a MS-DOS computer. As such I was confident that the command set would be reliable.I wrote little test scrips in Python to check that each command worked as described. It was all OK until I go to the command that sets the receive frequency. It didn't work.At this stage, I wasn't sure I had the correct frequency command. There was just enough ambiguity to cast doubt. Also I am at the bottom of the Python learning curve.I did some 1990's style fault finding with my dual signal HP 54645D scope and also used by GPIB to HP logic analyser / HP 54645D breakout board.After a significant effort, I found multiple faults/errors:The command I initially used to set the frequency was not correct.The 16 bit DAC is ex-parrot.The lowest 8 bits of the digital input to the DAC are frozen so there is still another fault upstream.So if anyone has a Burr Brown DAC71-CSB-V 16 bit DAC they want to sell, I want to buy. Digikey probably ran out of stock in 1992. There are some devices on e-bay, but that is a lottery. It is too expensive for me to return a defective device.

author: Kean
author_rank: Unknown
timestamp: January 17, 2025, 03:27:35 am
content: Quote from: dazz1 on January 17, 2025, 03:03:41 amIs this a Monty Python reference?There are some DAC71-CSB-V listed on eBay.Otherwise, you might want to post in thebuysellwantedsection for more visibility.

author: dazz1
author_rank: Frequent Contributor
timestamp: January 17, 2025, 03:38:54 am
content: Quote from: Kean on January 17, 2025, 03:27:35 amIt couldn't be anything else

author: dazz1
author_rank: Frequent Contributor
timestamp: May 06, 2025, 07:09:14 am
content: HiCycling back to this project, I have copied the firmware eproms and attached them here for the benefit of members of the Electro-Metric EMC30 owners club. It is a very exclusive club with only one known member.I have been having issues with getting the gpib command to set the frequency. It hasn't worked for me. Not sure if it is a problem with me or the EMC30. I am having a crack at reverse engineering the firmware. Not the whole thing, just the gpib set frequency command. I am learning to use Ghidra. The firmware takes up about 10kB eprom space, so not a small amount of code.I have written a reasonable amount of assembler in the past, but reverse engineering someone else code is quite different.The EMC30 runs on a MC6809 processor plus a MC68488 GPIB interface device.I am not attempting to completely disassemble the firmware. That would require a LOT of work. Just aiming to trace one GPIB command to understand how it works.My Wavetek 2520 signal generator runs a MC6502 plus MC68488 devices, and that is being problematic with gpib commands. So maybe what I learn with the EMC30 can be applied to that as well.