Archive for the VHF 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.

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New SDR receiver in the shack

Posted in Electronics, VHF on 3 September 2018 by iw0ffk

airspy

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.

cn15

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.

2018 6m ES season

Posted in VHF on 20 August 2018 by iw0ffk

In 2017 we had the first signs of change in 6m dx activity with the intensive use of JT65 mode during the e-sporadic season.

This year the JT65 has been almost totally replaced by the faster FT8 mode that permits to complete a PC QSO in about 60 seconds.

We had days of strong and long openings with JA/BA and US, sometime till late night. Tens of FT8 DX stations decoded at every period, often with speaker copy.

There are pro and cons of the massive use of WSJT modes on 6m.

PRO:
– there is only one frequency (50.313) and everyone makes CQ and QSOs there. One can easily check the propagation and the openings simply by monitoring.
– in the past only the CW operators could get some results in 6m DX, now there are much more hams on the Band.
– the WSJT and his clones are connected to pskreporter , a real time propagation map is obtained by the users automatic spots.
– with a minimal remote setup, one can work DX easily with a smartphone

CONS:
– there is only one frequency (50.313), it’s easy to have a neighbour that calls in the wrong period or work single ES hop stations during the intercontinental openings…or calls for HOURS alone !
– I find this way of dxing very tedious, almost no op skill involved, just make a double click on a callsign and cross your fingers.
– the FT8 on 6m DX is a time consuming activity! One has to follow the decoded text all the time and reply quickly, often the openings are very short and the system is still slow as a snail compared to the CW (but it goes 10dB below)

This year I worked 5 new countries in FT8 mode (PZ, VP9, ZF, HH, KH2) and 1 in SSB (Z6), so my score now is #200 + 5

I want to keep the DXCC worked in the usual modes separate from those worked on FT8, Although they use the same field of play, they are different sports.

 

ESP8266 JT65a beacon up and running

Posted in VHF on 9 May 2018 by iw0ffk

Click qui per la VERSIONE ITALIANA

The old 144 MHz beacon transmitter has been replaced with a brand new one.

The goal was to have a JT65 simple beacon without the need of a dedicated ssb transmitter and at the same time maintaining the very useful control via Telegram.

The WSJT mode in use is JT65 submode A, our band plan limits the bandwidth of a beacon to maximum 500 Hz.

The microcontroller is an ESP8266-12E and the radiofrequency is generated by a DDS AD9959. The AD9959 is a very nice DDS, it has four outputs and, if the internal clock runs at 500MHz, can generate up to 200MHz. The down side is the tuning word limited to “only” 32bit.
The external reference clock can be multiplied up to 20 times by the internal PLL to obtain the needed 500 MHz. The AD9959 demo board comes with an installed 25MHz oscillator but unfortunately it can’t be used to generate a good 144MHz JT65 signal. With Pino IK0SMG we measured too much drift in the short time and the JT65 results not decodable. Now the reference is 100 MHz OCXO and the PLL multiplier has been set to 5x. The minimum phase noise is obtained disabling the PLL…we must be content with what we have.
Claudio IZ0TYD gave me a surplus 10MHz GPSDO and I will try to catch an higher harmonic in order to further improve the Reference.
The Internet connection is mandatory for the Telegram exchanges, so it’s used also for the time synchronization needed for the JT65 protocol.
The beacon is installed in our HF contest farm in Ostia Antica, close to the sea.
In that location we already have a wlan, internet access and an headless Raspberry Pi that handles some automations and security tasks.

2018_04_jn61ds_01_ddsbcn

 

The microcontroller programs 144.461 MHz on the DDS then the amplitude is gradually shaped to obtain the morse code without clicks. The JT65a modulation is generated programming on the DDS the pre-coded tones in the correct order at the correct time without phase jumps.

beacon

The beacon transmits for 2 minutes the message in telegraphy, then 3 minutes of JT65a.

Everyone on the beacon Telegram group can send simple commands to the beacon, like attenuate the output power in steps of 3dB up to 12dB or request a steady carrier.
As example to insert the 6dB attenuator, just write on the group /att6db
For a complete list of commands, write /help

Istantanea_2018-05-09_20-59-13

 

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.

2xhen

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!

10G DXCC+ODX = 1100+ km !!

Posted in VHF on 30 August 2017 by iw0ffk

In the latest days very good conditions of ducting over the Mediterranean Sea with huge signals from Spain in VHF & Up bands.

2017_08_24_09_ffk

Silvano I0LVA has opened the path, then many OM maked skeds with Vicente EA5YB.

I did it in the afternoon (after three attempts at 1 hour interval).

EA5YB in IM99VC 10GHz SSB QSO SEA DUCT

10G_EA5YB_IW0FFK

Here the Vicente EA5YB working conditions

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.

10G

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.

1296M

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.

20170821_114708