Posts by DJ0MY

Here is Part 2 of my modification:

Even if this LNB type might be obsolete within very short future (I still have a spare one that I am going to use for the TCXO mod) perhaps at least this serves as learning material and inspiration for future modifications of other hams.

As mentioned above the original mod still requires quite some drive into the LNB to get the PLL chip to lock.

So here I used the PA3FYM approach and installed a parallel LC cirquit into the line going to the meander line.

I was too lazy to remove the 11 ohms resistor from my first original modification. So I've put the parallel LC circuit just behind it in series.

The mod is very simple – with lid open and PCB visible just cut the trace towards the meander line and insert a 120pF capacitor and 330nH inductor (both SMD 0603 size) and solder them in parallel. (see pictures of my mod attached)

Ideally if you follow my first mod after reading this, just do not install the 11 ohms resistor and solder in the same place the parallel 12pf+330nH. That is in my opinion the most convenient location, in order not to interfere with the lid.

Result:

Now 0dBm drive and even -6dBm drive (did not test to go lower) is fully sufficient to make the PLL chip lock. Full success !

73 de Oscar DJ0MY

NOTE:

This post has been edited to correct the wrongly posted 12pF into corrected 120pF values (I will also try to update the photos)

Excellent suggestion to just isolate the XTAL from the top side of PCB - much easier mod - thumbs up ! Thanks Johannes for sharing...

73 de Oscar DJ0MY

Quote from ON4CJQ

How about using a SATfinder,but is 950-2150 rx. Any tried this?

73's Jerry

Jerry the question here was about NB transponder....

Your question belongs to WB transponder, hi hi....

(but in fact a sat finder with built in screen and RX works well for receiving WB beacon)

73 de Oscar DJ0MY

I would like to document my single cable GPSDO feeding modification made to my VENTON EXL-S LNB.

While modifying this LNB for external GSPDO feeding is extremely simple (just remove original XTAL and feed GPSDO signal externally via a short SMA pigtail into the original pins where the XTAL was previously located from the bottom side of the PCB) and was working here well for a few weeks, I did not want to have a separate cable, so I was looking for a cleaner solution.

The VENTON EXL-S is using a 25 MHz PLL and due to it’s long circular waveguide I find it extremely well suited for use with the famous dual band POTY feeds. Also due to PCB and case layout it has quite some convenient space inside for adding modifications. This LNB type is also nice since it comes with a very efficient dielectric lens that can be removed and used for the POTY dualband feed also.

For feeding the GPSDO signal to the LNB via the main coax cable I am using the triplexer circuit described by OH2AUE here in the forum and on his website:

OH2AUE Document (see page 15)

Here are roughly the steps that I followed:

1.       Open LNB case and remove all screws and open the lid

2.       Unsolder center pin of F-Connector (removing the solder works well using solder wick) until the centre pin is noticeable loose inside the PCB hole

3.       Cut carefully with a very sharp thin cutting tool several times around the PCB edge into the silicon that is used to glue the PCB into the LNB case.

4.       Use a very tiny and thin watchmaker screwdriver to VERY GENTLY lever the PCB out of the case. Do not apply to much force as the PCB is very thin and may break.

5.       Once PCB is removed turn it upside down and remove the 25MHz XTAL. This works best with a hot air station (cheap one for 35 EUR works well for this purpose) or use two soldering irons applied left and right of the Xtal. It will be very difficult to remove with just one soldering iron.

6.       Now turn PCB to upper side and cut the trace leading to the meander line (see photo)

7.       Also scratch away some of the solder mask and tin it

8.       Now place a 11 ohms resistor in series from the F connector pin to the meander line (see photo)

This approach I just copied from OH2AUE modifications documented here in the forum.

9.       Now add a 120pF capacitor (0603) in on top of the line leading from the F connector pad towards the PLL chip. Following this trace if useful because there is a convenient space available inside the lid.

10.   Add a 330nH (0603) inductor in series to complete the series LC circuit.

11.   Now just use a short piece of thin enamelled wire to connect the just created LC circuit with one of the two inputs of the PLL chip. I simply connected it to one of the conveniently located load capacitors from the original XTAL inputs (see photo)

12.   Put the PCB back into the case and solder the F connector centre pin

13.   Check for any short circuits on the F connector J

14.   Close the lid – LNB mod complete

With this mod and the OH2AUE triplexer I can feed my Leo Bodnar GPSDO directly into the triplexer (approx. 6-7dBm into the LNB) and the LNB PLL locks without any problems.

However, I noticed that with approx. 0dBm at the LNB it does not lock anymore….so this mod needs quite some drive. But since the output of the Leo Bodnar GPSDO was adequate I did not bother at first to improve this any further.

I will try to improve this later by adding a parallel LC circuit in series of the meander line and document here is successful.

Also going to try a TCXO mod for this LNB type to be documented here hopefully soon.

73 de Oscar DJ0MY

NOTE:

This post has been edited to correct the wrongly posted 12pF into corrected 120pF values (I will also try to update the photos)

Unfortunately, all my VHF/UHF capable ham TRX are unable to RX on 739 directly - except my hendheld Kenwood TH-F7E....

But on that frequency range it only accepts FM-W modulation (since it thinks its a TV broadcast band).....SSB is only selectable on lower frequencies within parts of the specified RX ranges.

What works very well however is my Yupiteru MVT-9000 portable hand scanner (equals Stabo XR2000)....I guess the well known AOR scanners should do a good job as well as most of the higher end models offer SSB demodulation.

73

@SWL - markro92: Any chance to add in addition to just the BB gain slider also a RF gain slider (for those SDR like e.g. RTL SDR which support different setting of BB gain and RF frontend gain)?

This way one could comfortably bring some of the strong LNB levels down a bit without the use of attenuators by just applying manual frontend gain settings.

Just a suggestion.....not high priority.

And great to hear about Airspy

Keep up your very excellent good work.

Before now all fellow holiday makers from central Europe take their portable QO-100 gear with them to their next EA summer vacations and start pirate operations please be advised that this special permit in EA is:

• limited to EA licensed hams only (no CEPT operations !)
• limited to SSB phone mode only
• a temporary permit valid until 26th of September 2019 only

For those of you fluent in spanish here is the original publication link by the Spanish ministry:

Lets hope AMSAT-EA / URE can get this successfully extended into a continous approval after this trial period and will be able to remove the above three restrictions.

PA1EW:

I also have also built the same kit here and mine also just shows one shallow dip around 2.41-2.42 GHz.....RL on 2.4 is around 17-18dB so good enough for TX and works excellently on a 85cm dish...

So do not worry - it should work OK.

73

@SWL - markro92:

Did you receive an e-mail to your t-online.de adress from Youssef, the author of SDR# and inventor of Airspy? He would like to offer you support with a Airspy sample hardware (many people here also use Airspy SDRs) and some software tricks for sample rate conversion....

See his tweet here and try to get in touch with him. He is a nice chap and very helpful. (and understands SDR "black magic" very well obviously)