Archives de la catégorie ‘Filter mobo’

Alexiares filter for home made SDR

Publié: 12 novembre 2017 dans Filter mobo, Project, SDR

The original OpenHPSDR Alexiares filter (aka “Alex”)  is particularly well suited for most short wave DDC/DUC software defined radio. This complex front-end is a mix of HPF and  LPF filters. The LPF "cleans” the transmited signals and is always “on”, the HPF is only active when receiving and makes a nice “medium width” and adjustable bandpass filter when combined with the LPF. As narrow bpf are not mandatory for DDC-base SDRs –they even could impair the MDS of the receiver-, this architecture is probably the best of breed  in term of filtering

Choosing the righ LPF/HPF combo is simply made by software, via a serial I2S protocol. This protocol also commands and controls many other gadgets : a low noise amplifier for the 6 meter band, a bypass circuit –filtering could be a handicap when dealing with spread spectrum transmissions for example-, a permanent 60 MHz LPF used as an antialiasing filter, and many antenna and receiver switching to select a set of antennas, use a specific external BPF, amplifier or transverter, , select the first or second ADC for receiving, or use the second ADC when transmitting and using the pre-distorsion (aka “pure signal”) function.

But… oh, wait !… Alex is not sold anymore by the TAPR! The bare pcb is almost impossible to find. And anyway, Alexiares cannot be used with certain configurations. Most ham using a Red Pitaya, for example, are looking for a filter board with an I2C protocol. Guys wishing to build a Hermes Lite prefer to use a simple “parallel” protocole that mimic the “J16” 7 bits output (also known as Hermes/Penelope in PowerSDR’s config screen). And people playing with some “kilowatt SSPA” frankly don’t care about the LPF section of Alex : they only need a way to control le kW-class lpf they intend to use, without compromizing the “Hermes/Alex way of combining LPF and HPF filters”

That the reason why I decided to build a new set of board, fully compatible with Alexiares… but with some differences. The two main boards remains the HPF and LPF filters, both of them beeing built on a 10×10 piece of pcb, both of them needing a simple “positive common/ground switched” logic. Depending on the kind of SDR you intend to build, you can drive these two filter with a “plain old” I2S serial interface, an I2C interface, add an antenna selector, add a preamp/transverter/specific filter crowbar, choose to integrate a Solid State Power Amplifier control unit, and adapt you own antialiasing filter depending on you sampling rate (60 MHz for the Red Pitaya or Hermes/Angelia/Orion board, or 31 MHz for the Hermes Lite V1.0 or V2.0).

In the near future, a multi-purpose Tandem-match 33dB coupler will be added to this set of pcbs (for pure signal and vswr control)

Warning : this project is not yet fully tested. It could include a certain number of errors. As long as a full set of prototype boards haven’t been assembled and tested, use these files with caution (and at your own risk).

All these files are open source (CERN Licence) unless specified by it’s respective authors. All schematics from the OpenHPSDR are protected by the OpenHardware licence. The Mentor board intellectual property belongs to ON7EQ. The whole project has been completed with Kicad EDA, an open source CAD software developped by CERN.

– Alexiares_LPF : 


A LPF board, stritly using the very same set of filters as the original LPF, and able to widstand 80 to 100 W PEP. Toroids are T68, relays are able to widstand a 3 amp current. This board is based on a 4 layer pcb. All caps are 500 V ATC-like components. This board can be shielded in a 10×10 cm metal box.The Kicad schematic, pcb and gerber could be found on github on this link.

– Alexiares_HPF : 

HPF bottomHPF up

A HPF board with a integrated 6m LNA and a bypass (passall) filter section and a low noise amp (MMIC). It’s a simple 2 layer pcb using small signal relays and T50 toroids.This board can be shielded in a 10×10 cm metal box. The Kicad schematic, pcb and gerber could be found on github on this link.

– Alexandrie :

Alexandrie dwnAlexandrie up

A full featured SPI interface fully compatible with the Hermes serial protocol (J6 connector). This board has the same 10×10 form factor than the HPF an LPF pcb’s.The Kicad schematic, pcb and gerber could be found on github on this link.

– Alexi2C :

Alexi2C dwnAlexi2C up

A fork of the DC2PD interface that converts the I2C protocol used by the Red Pitaya (Pavel Denim’s firmware). This board can directly drive the LPF/HPF set of filter as it includes a pair of ULN2803 drivers. This board could also be used without any I2C decoder. In this case, the parallel bus of the SDR is directly plugged on the board and the pair of ULN2803 could be used in “J16” mode. This board is using a ”half size” format (5x10cm) The Kicad schematic, pcb and gerber could be found on github on this link.

– Alexiares_LPF_RX_In :

Alexiares_LPF_RX_In bottomAlexiares_LPF_RX_In

A specific 60 MHz lpf with a 88/108 notch filter and a TX/RX relay. This board is in fact a sub-section of the RX High-pass filter that couldn’t fit on the HPF board. I decided to enhance the characteristics of the original filter, with a 7th order “M-Modified” LPF. The LPF section acts as a strong antialiasing 60MHz filter and the two elliptic rejection frequencies are centered on each side of the FM broadcast band. This way, one could not be disturbed by FM signals located in the 4th Nyquist zone heard on the 21, 24 or 28MHz band. One side of this filter –the output- goes directly to the HPF input, the other side is ended with a relay that isolate this filter from the RX path when transmitting. During TX, a small amount of the transmited signal is so redirected to the second ADC and used by the pre-distorsion (pure signal) control software. This board has a small footprint (5x5cm). The whole board or only the filter itself could be shielded. The first option is highly recommended; The Kicad schematic, pcb and gerber could be found on github on this link.

– Alexiares_Coax_Out :

RX_Ant dwnRX_Ant_up

A set of two 5×10 boards for the RX and the TX path, used to switch antennas (3 max), external filters or low noise amplifiers, transverters, and select the current ADC. Both board can receive a peripheral shielding. The Kicad schematic, pcb and gerber could be found on github on this link.

– Mentor :

Mentor dwnMentor up

A Deluxe Arduino-based control board for SSPA designed by ON7EQ. This board handles information comming from the linear amplifier (voltage, current, temperature, vswr, direct power….) and takes action in case of difficulties (drives the cooling fan, shuts the amp down, and alerts the Hermes main board). The Kicad schematic, pcb and gerber could be found on github on this link.


Hermes Lite by KF7O

Publié: 24 novembre 2016 dans Filter mobo, SDR

I never mentionned it on this blog or on the Electrolab’s Wiki, but some time ago, I built an Hermes Lite SDR. It’s a nice piece of hardware that Steve KF7O gave to the community. I said “gave”, because it’s a full open hardware, open software project.

This rig is a true DDC/DUC SDR, with a 12 bits/60 Megasamples ADC (an Analog Device AD9866 transceiver on a chip). It gaves me hours of fun, and could be used as a serious baseband bedrock for many extensions (transverters, power amps etc).

From a software point of view, this small and low cost SDR is fully compatible with the TAPR’s Hermes high-end system. It could be followed with any kind of Hermes client software, like OpenHPSDR GNUradio, GHPSDR3-Alex….

double réception hl deca

This is a snapshot of a dual RX config. of OpenHPSDR behind the Hermes Lite

The total cost of this system is around 100 to 150 $/€. The version I built (the one here described ) is allready deprecated, and will be soon replaced by a compact, monoboard 2.0 edition.

Anyhow, let’s take a short tour of this project


cote hermes

On top, the BeMicro SDK “usb key”, supporting the FPGA. The Hermes lite itself is the small green board located on the right of the BeMicro, followed by a simple output board (two transformers winded on binocular).

On the lower side, a bandpass filter (tcheb) originally designed for the Softrock Mobo 6.3 project. This bandpass filter is used in transmit mode only. Different receive tests show no difference between an “barefoot” Hermes Lite and a filtered one.

The bandwidth of each filter has been enlarged to lower insertion losses

Hermes Filter bw 1-8 to 24-3 MHZ

On the right of the case, a 10 W power amplivier (a TAPR’s original Pennywhisle).

As the Hermes Lite is note able to directly drive the Pennywhisle, a 20 dB/1W driver, using a single operational amplifier (OPA2677)  is inserted between the rig and the amp

amp recto

This home made amp has been designed to fit into low profile machined cases (former MCL 3dB hybrid couplers sold a few $ on eBay)


The pennywhisltle itself is mounted on the rear panel. A better amp, like the 20 W G6ALU (particularly VK3PE Glenn’s version) would have been more suited… but I keep this amp for the H.L. 2.0

So far, this combination gives good results and can drive a 300 W PEP power amp without problems



On the other side of the case, a CW Curtiss Keyer (former MFJ keyer), the linear power supply (as Steve said : “lot’o heat”… but with a good and silent fan, it works as advertized.

The brown board with 5 connectors is the switching interface between the Hermes Lite and the filter board

ULN sw

This is a quick and dirty hack with an ULN relay driver.

Filter mobo phase One : over

Publié: 3 juillet 2009 dans Filter mobo

The design of the 8/16 elts filter mobo has been completed. Now, we can launch a proto and see if what’s on the paper will work as advertised.

I still have to finish the “BCD command board” (this one was not urgent and mandatory for Alex’s project) and a fully new switching board for the high power version of the filter.

Anyway, here is the full and final production of the different elements of the filter.



This card decodes an I2C bandswitching command comming from Alex’s microcontroler, and sends the corresponding signal to one of the multiple input of an ULN2803 (relay driver)

Each I2C interface has a selectable adress, determined by a matrix of 2×3 0 Ohms pullup resistors.



Quite a lot of “invisible changes” have been made in the position of the traces, tuning of each component size and position and so on… Enough space has been preserved to solder a “U” shaped shielding located all over the central bus. This will probably enhance input/output isolation and minimize all RF re-injection risks.

The FILTER DAUGHTER CARD remains unchanged…


… excepted some angle stripline to try to keep the input impedance as close as possible to 50 ohm. But the angle connectors binding this daughter board to the mobo will certainly destroy the quality of the line. Anyhow, it’s not  a reason to have “ugly traces”. I hope the next “filter” bloging wil have some real picture to illustrate the story.

Back to work

Publié: 21 juin 2009 dans Filter mobo, SDR

After a looooooong stand by and quite a lot of miles by plane, car and train, I’m back to work.

Some minor modifications have been made to the filter mobo (larger and adapted strip line at the input and output).


The mobo has heavily been redesigned : for a better ground plane and better coupling, pass-through relays have been replaced with gull wing components. This way, a unique 2,9 mm HF bus (50 ohms strip line) goes from relay to relay. RF flow on the upper surface has very limited accidents.The I2C command board will probably be redesigned within this week, to comply with Alex’s wishes (better integration, no address assignation by default).

A Minimelf Diode (4148) pad has been added close from each relay. But as most of the “form C dual circuit/dual pos” DIL relays are polarised; it won’t be necessary to add this component most of the time.

The central bus is far from perfect an will be optimized all along this week.

The 100 W++ filter mobo will probably have a different design : same command daughter board, same filter daughter boards, but 4 separated relay boards (pin to pin compatible with the command board) will concentrate the switching stage. Wiring between filters and relays will be made with Teflon coax cable. I’ve try to use the pcb design with higher power rated relays, but in vain.

CAD re-design of the whole project

Publié: 13 avril 2009 dans Filter mobo

The mobo and daughter cards are slowly redesigned under Kicad. The final result will probably be simpler and a little bit more optimized, as the software is surprisingly powerful.

The daughter card is almost finished. I must solve some problems concerning the grounding zone and learn how to correctly print the postscript file to etch a prototype, but it’s a matter of days.

The main mobo is far more complex and Kicad is trying to play with my nerves, inverting some components without logical reason. I’m sure I’ll have the last word J

The 3D result is a little bit smarter than the qwick and dirty ExpressPCB, isn’t it ? It’s anyhow a marvelous function to hunt misconceptions and wrong placements.

Filter mobo, first prototype

Publié: 4 avril 2009 dans Filter mobo

Some component are missing… I cannot go further.  But








As I was out of eyelets, I couldn’t have metalized holes… that’s why relays are soldered high above the pcb. Surface mount devices and/or flater relays should be used on the final mobo. I’m loosing too much space with those one.

Dauthter cards are fitting perfectly (excepted that they are a little bit too short… something lile a thenth of an inch). I’ve completely messed up with the Command daughter boards, inverting the printout without noticing it…. this is why so many wires are running on the back side…

So far, bands are switching correctly. I have to order a handfull of ULN2803, PCF8574, 4028 and other things next monday

New batch of PCB

Publié: 30 mars 2009 dans Filter mobo

The first proto showed some misconceptions and a lot of cabling mistakes. The humain brain … well, MY brain is not able to “mirror” the pinout of a simple relay…

So I had to etch a new mobo again. As the former daughter cards were also wrong, I draw a batch of daughter boards.

From left to right :

First column : a set of filter daughter cards (one “backside”, four “components side”)

Second column, from top to bottom :

– Command daughter board, BCD to 2xOctal

backside and component side

– Command daughter board, I2C to 2xOctal

backside and component side

Third column : the debuged new mobo (hope so)

Fourth column : the wrong one with some components.

…. time consuming 😦

Nothing will be sodered tlll next month.

It fits !

Publié: 12 mars 2009 dans Filter mobo

This first picture is for…. some snowboarder living in Singapore

…. softrock on the rocks of the french Alps


the local altitude is 2800 feet (that’s low for us), mountains around reach 6500 feet to 13 000.ft The QTH is located approximately 45 miles away from the Mont Blanc, the highest mountain in Europe (15767 ft)

the UWB/level converter/audio input is installed… and it fits perfectly


A close-up on the knitting


and a general overview of the SR, Alex’s Mobo, the frequency display and the PCB of the filter’s prototype … all that stuff fits in a 5’1/4 drive enclosure.

I did’t allready tested the UWB… the pic is not yet programmed.

Filter mobo, first prototype

Publié: 9 mars 2009 dans Filter mobo

At last, I found some time to play with expoxy.

As I still cannot make a real “black” film, I’m still unable to use photo processing to print my pcb. For this reason, I used the “laser toner transfer” method. And, after several unsucsessful tests, I found the good temperature, the right paper, the good pressure, the best toothbrush (to scrub the paper)…

… And I got this. It’s my first pcb done with this process.

Phase I : printing, transfering (with a laminator), scrubing and etching

The “white dust” covering the surface is the paper left on the toner

to reach this quality, I had to sacrifice about 10 sheets of paper. Borders are absolutely clean. The only drawback of this method is that important flat surfaces are far from perfect. The toner deposit is not constant.

Phase II : cleaning the first side

After cleaning the board… it seems to be usable. I hope the irregularity of the main ground plane won’t affect too much the quality of the circuit

the following picture shows a filter daugter card and the interface described some time ago (level interface TTL to 3.3v, and Audio interface with a pair of Triad transformers). Laser transfer technique works better on small boards. The trace between the two circuits is a 0.010 inch line (0.25 mm), without any cut.

Phase III : printing the other side (ground plane and vias)


positioning the other side after drilling 6 marks

drilling the board

I broke my last 0,9 drill, which is absolutely necessary for the HE14 right angle connectors. I’ve no more 1 and 1.1 mm drill…

The first daughter card was bad (connectors where not in front of mobo’s connectors). Dimensions on the cad software are right. It’s probably a wrong printing ratio or something like that.

Next step : tinning the board to protect it against oxidation, plating the vias with silver compound… and looking for drill on ebay

The small company I spotted to print my filter mobo is unable to draw .010 traces. I had to partially redesign the data bus on the central “island”.

As I was under my CAD software (still the same… I know, it’s a shame) I took some time to make a I2C command board (that’s Mike’s idea)

above, the redisigned BCD daughter board (I made some mistake on the former design, the central connector had a quarter inch ofset)

the lower board is the I2C one. The electronic diagram has been “pirated” from the superb CDG2000 schematic

Still the same size, still the same footprint. I think I will draw a simple “parallel hard wired daughter card” for people wishing to use a basic rotating switch, just to keep the design universal and adaptative “on the go”.


Meanwhile, to test my first “home made pcb etching lab”, I’ve printed the I0CG “SSB K1 mod” . First results are “just usable”… I’m far from a real “professional looking” board. But it’s encouraging.

Anyhow, this is another story.. let’s focus on the filter. Next time, I hope I’ll be able to post some picture of the filter mobo