Archive for the Electronics Category

Tx inhibit: how to simplify the TX/RX sequencing

Posted in Electronics, VHF on 21 September 2018 by iw0ffk

When I started to prepare my home 10 GHz station, the designated transceiver for this band was the Yaesu FT-817, because I knew that many microwavers use it as a IF for their transverters but mostly because I already had it and pratically unused.
The little Yaesu has the input signal “TX Inhibit” on one of his ACC pins, so I used it in my Eyal-Gal TX-RX sequencer of a previous post.
The TX INH operation is simple, if you put a voltage on this pin (12V), the transceiver will never transmits radiofrequency even if keyed.
So it was enough to use a couple of wires that bring the PTT and the TXINH signals from the transverter on the rooftop down to the FT-817 in the shack.
When the PTT gets closed, the transverter starts the RX->TX sequence, the TXINH is at +12V and no RF power comes out from the RTX. At the end of the sequence, the TXINH is switched to GND and the transmission can start safely. Same story for a mast mounted preamplifier instead of a transverter. Also a linear amplifier can be keyed in that way, in order to assure a cold switch (doesn’t work on CW full-break-in of course).

Why this approach is MUCH better than the common sequencers?
The answers are:

  1.  because there is no need to wire the microphone, Morse key or PC PTT to the sequencer box anymore: the sequence starts when the transceiver closes the PTT, so everything has to be connected on the transceiver in the usual way.
  2. because one can safely use the features of the transceiver like voice keyer, cw keyer and memories, rtty macros, auto tuning etc. without damaging the device on the rooftop.
  3. because it’s more “fail-safe”. For example with the usual sequencers one can accidentally press the key “SEND” on the transceiver’s panel and the preamplifier’s device is fried in a millisecond.

Really I don’t know why Kenwood and Icom doesn’t have on their rigs this great feature that helps who use preamplifiers and/or transverters and/or linear amplifiers. Anyway it’s easy to add an external circuit to obtain the same result. This schematic is for my 10GHz transverter that works with an IF on 70cm, it’s just an example.
tx_inhIn few words a negative voltage is sent to the transceiver’s ALC input to inhibit the RF output until the device on the rooftop is fully switched to TX.
I tested this circuit on a Kenwood TS2000 that needs an ALC voltage of about -7V to completely cut off the RF output. The Icom rigs needs about -3V, in this case the 68k resistor and the trimmer have to be sized to meet the ALC limits. The DC-DC converter can be replaced by a 9V battery. The calibration is very easy: connect the transceiver to a dummy load, transmit in FM and turn the trimmer until the RF output power is completely choked.

The video below shows the TX inhibit intervention at every RX to TX, the ALC indicator goes to the full scale (no RF output) then it’s released and the RF can come out. In CW one has to send a “dot” before transmitting, as a conventional sequencer.


New SDR receiver in the shack

Posted in Electronics, VHF on 3 September 2018 by iw0ffk


Recently I bought an SDR receiver in a dongle form to replace the old RTL-SDR in use on the IF of the transceivers, in order to have a panoramic view of the band.

The dongle is Airspy mini that has a good balance of quality and price, 12 bit ADC, samplerate up to 6 MSPS and an acceptable dynamic range.

My purpose is to have a detailed view of the noise floor on the 10GHz band to detect any change when a cloud usable for rain scatter is pointed with the dish.

The previous RTL-SDR was connected to the intermediate frequency of the transceiver, just after the first mixer. This time, thanks to the suggestion of Pino IK0SMG, I moved the RF tap to the input, after the front-end and the filter.

Actually I use a Kenwood TS-2000 with the 3cm/23cm transverters that are placed on the rooftop. The transceiver is tuned to 432 MHz and 144 MHz respectively on the converted frequencies of the two microwave bands.

Fortunately the TS-2000 has a TMP connector already mounted on the TX-RX 2 board, where the VHF and UHF paths are joined before to enter in the first mixer. This connector (CN15) is used in the factory for the band pass filter adjustment and it’s perfect to tap off the signal for the SDR without desensitize the main receiver.


I’ve done some test and the spectrum can be zoomed-in down to a dB per division.
I taken a short video of the 2m IW0FFK/B beacon. The beacon is controlled via Telegram messages, first it was set to “CONTINUOUS CARRIER MODE”, then different RF attenuators have been inserted. The SDR measured amplitude match the values of the attenuators! FB

If you want to send commands to the beacon, join the beacon’s Telegram group by clicking this link.

IQ0OS/B moved and enhanced -> Telegram beacon !

Posted in Electronics, VHF on 24 March 2018 by iw0ffk

The 144.461 MHz ARI Ostia beacon changed ID and has been moved in JN61DS. Actually is running with my callsign but I hope it will be a temporary solution to grant the presence on air of this historical beacon active for about 25 years.

Thanks to Pino IK0SMG, Emilio IK0OKY and Fulvio IK0YFK in few hours in a rainy and windy Sunday, the beacon has been installed in our HF contest farm in Ostia Antica. The output power is 3 Watts and the antenna is the same omnidirectional horizontally polarized double hentenna.


The new site has full internet access, this gave me the opportunity to made some changes. The RF section has been realigned, just in case, but was ok.
I replaced the microcontroller Pic 16F84 that worked for the last 10 years (and still works) with a more recent ESP8266 (that has WiFi capability) and wrote a new firmware.

Now the new beacon can be instructed with a smartphone to connect to the WiFi Access Point, then it can be controlled by a Telegram bot.
By writing messages in the IW0FFK/B 144.461 Telegram Group , the beacon’s owner can power it on/off, change the callsign, locator and qth.
Other users can change the morse speed, just for fun, or ask the beacon to transmit a steady carrier for maximum 120 seconds, in order to do some measure like an antenna plot with the G4FHQ’s software.

plotlfaffk beacon_bot

If someone is interested I can share the ESP8266 executable that can be customized easily for every VUSHF beacon.

More improvements will come!

Summer works 2017

Posted in Electronics, VHF on 30 August 2017 by iw0ffk

Usually I spent part of my August holidays to do some work that can’t be done during the working days. In the latest months I prepared some parts to be installed on the rooftop. This year has been focused to 23 and 3cm bands.
Stuff list:

The GPSDO has been placed near the antennas and supplied 24/24/365 with POE shared with a WiFi Access Point. It provides the reference signal for the 9936 MHz oscillator and for the ADF4153 inside the LZ5HB’s transverter.


With Pino IK0SMG we measured the DF9NP’s oscillator that works well and has a good phase noise.

Then we measured the 10G power amplifier and after some work the maximum gain of 8+ dB has been centered to 10.368 MHz. My driving power is little more than 30 dBm, the resulting power to the feed is now 37 dBm.


The 23cm amplifier uses a MRF186 device that has a gain of 11 dB @ 960 MHz, when used at 1300 MHz the gain drops around 9-10 dB. The RF power of the transverter is 2 Watts, so the power in antenna is something less than 20 Watts. Not so much but it’s better than before. The transverter, the amplifier and the RX filter (necessary) have been placed in an aluminum box on the mast near the antenna.


IC-7300: more antenna connectors with Arduino!

Posted in Electronics, VHF with tags , , , , on 12 April 2017 by iw0ffk

I wish to use the IC-7300 on all my bands, but the problem with this rig it’s always the same: too much frequencies for a single antenna connector and I don’t want to swap the coax all the time. On the market there are manual coax switches, but there are not so handy for a remote use…and this one is cheaper.

So, in a rainy Sunday I have built this 1×3 antenna switch controlled by Arduino. I already done something similar in 2009 with a PIC, this time I choose Arduino because it does not need of any programmer to write the code on it, just the USB cable. In the past several OMs have sent their empty PICs to me and I have sent them back programmed. A single project usually don’t worth the cost of a PIC programmer.

This should stops the foot traffic, everyone can load the code in the IDE and write it into the chip with a click.

This 1×3 ant switch is made with few generic electronic components around a “Nano” (ATMEGA328), but the code can be adapted to any ucontroller. It is powered by the transceiver (pins 2 and 8 of the ACC connector) and reads the frequency from the “Remote” jack. It can be fixed directly on the antenna’s connector by using a male-male PL259 adapter. Into the RF box there are three Finder relays model with gold plated contacts. The values of attenuation and isolation between the ports are good:

28 MHz – att. 0.11 dB – isol. 40 dB
50 MHz – att. 0.11 dB – isol.35 dB
70 MHz – att. 0.12 dB – isol. 32 dB

The microcontroller and the rest of the parts are in a separate box to avoid interferences.

The IC-7300’s range of frequency 30-74800 kHz is divided in 24 sub-bands, every sub-band can have associated one of the three antennas output. The right antenna is selected automatically. Simply it remembers the last selection.


Ask me the source code to my address. does not permits to upload zip files.

Icom IC-7300 RX Antenna mod

Posted in Electronics with tags on 11 March 2017 by iw0ffk

I like this transceiver, good receiver, fantastic DSP filtering and NR, excellent GUI and many goodies like the automatic record of QSOs triggered by ptt/key or the RS-BA1 software that shows the waterfall on the PC screen (it works ok also in Linux wine).

Probably Icom has decided to limit some capability of this model for market reasons. The IC-7300 has only one TXRX antenna connector and no RX input, but it’s easy to add a connector on the back and, inside, there is enough room to place a coax relay.

The relay can be mounted on a shaped aluminium bracket fixed to the transceiver by two screws that fix the RF-UNIT board to the chassis.

The adapter has been made with a female TMP connector and a SMA-M to SMA-F transition (used as a wear protection for the connectors of the instruments).

The external ATU supply connector can be moved away, like on the IC-756, and replaced by two pieces of copper pcb board that holds the switch and the coaxial connector.
The orange wire of the ATU is used to energize the relay.

This mod is fully reversible and the transceiver can return in his original status in few minutes.

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Now the IC-7300 can be used also as a second receiver for the 6m or for monitoring the IF of the FT-817, connected to the 3cm transverter.

Hacking the Spectrum Analyzer Siglent SSA 3021X

Posted in Electronics on 29 January 2017 by iw0ffk

ssa3021Last year  in the laboratory where I work we bought two Siglent SSA 3021X 2.1 GHz Spectrum Analyzer for generic/every day use. It’s a nice cheap object with all the functions of a modern digital instrument: colors, memory and math for traces, ethernet access, usb drive support etc.
After a while I found some bug in the software (v 7.03), as example if a screenshot image is saved in the internal memory with spaces in the filename, then it’s impossible to delete….
So I googled for a firmware update and casually found a thread on EEVBlog’s Forum where a guy shared the root’s user/password to log in the instrument with a telnet client. :-)

The big brother of the SSA3021X is the SSA3032X 3.2 GHz SA that has the same hardware of the SSA3021X. The instrument works on Linux, Busybox is running, and it’s an easy job to edit a configuration file and upgrade the SSA3021X to SS3032X with all the options enabled (tracking generator included) and extra BW filters 1Hz and 3MHz (!!!)

This works with installed firmware version 7.07, probably Siglent has corrected this bug on the newer firmware releases, but for sure I don’t need further updates on these units…