Wednesday, October 21, 2020

QO-100 LNB Comparison

My downlink (DL) is realized by using an old 40cm off-set dish on my roof deck, something I mentioned before. On recommendation of an old friend, I bought a Venton EXL-S Rocket Single LNB. So far so good, this LNB served me on many contacts. Using the beacon feature of SDR-Console made it possible to have those contacts. However, during my tests using analogue equipment, drift from this particular LNB was noticeable.
I understood the Venton LNB is primarily useful with with POTY "dual band" feed, as it keeps the centre hole to a minimum. Fair enough. 

For my setup, I decided to use two separate dishes for UL and DL, hence, the size of the DL LNB is irrelevant to the UL feed geometry. As a matter of experimentation, I replaced the Venton LNB with an Octagon OSLO LNB in the 40cm DL dish setup. This LNB was purchased many years ago, when I was active on 3cm rain scatter and wanted to experiment a little bit with commodity gear. To my surprise, the Octagon LNB is a lot more stable, once at temperature. It also appears to be more sensitive than the Venton. Aperture is the name of the game here, I figure. Hmmm, maybe I should have used this LNB from the get-go and saved the few Euros by not buying the Venton LNB.

Still, there might be a use for the Venton LNB. As mentioned in my previous post, I am considering to use a single dish for DL and UL. With its smaller form-factor, the Venton Rocket might be the better choice when placed inside the UL feed helix in a single dish arrangement.

I will post my further experiment on this blog, so, stay tuned.

BTW, occasionally, you might be able to hear me on the transponder. Feel free to give my a call ;-)


Monday, October 19, 2020

QO-100 update

Not much to report, other than I shortened the RG-6 coax for the Up-Link. The length should be about 3.5m, however, I have not measured the length yet. In order to achieve the shorter transmission line, drilled a hole into a window frame relatively close to the UL dish. This allows the power amplifier to be indoors. 

By now, I made contacts in side-band from Brazil to Thailand. The occasional rag chew QSO confirmed that my signal is loud enough to not be difficult to listen to.

There is a plan of using the UL dish also for reception. The added gain in the DL might make it easier to operate with a full analogue setup. Although, the LNB being placed in the center of the feed-helix might compromise the UL signal. Something to experiment with...
Further down the line, I might acquire a larger off-set dish, e.g. 1m, mainly to add some gain to the UL.



Sunday, October 11, 2020

QO-100 thoughts

The humble listener/follower of my station or posts might have experienced a certain lack of enthusiasm about operating on QO-100/ Please do not interpret much into this. The satellite is great. Probably the greatest any Oscars had ever been by this date.
However, once the setup is done, the fine tuning is somewhat frustrating.

What to look for?

Ideally, in my world, one would be going fully analogue, i.e. using only pure receivers and transmitters.
Does that justify the effort by the operators of the satellite? I don't think so!
Hence, we also should look into modern techniques, such as SDR.

Well, this is exactly the spot I am struggling with. I got the equipment for both, analogue down link and digital down link. I operated with the satellite using both. Concerning the up link, I an analogue only. 

What I used so far (RX - TX):

  • RSP1a - FT817
  • FT290R2 - FT790R2
  • FT736R (RX+TX)
Any of the setups has advantages and disadvantages. 

For the time being, I am using the RSP1a - FT817 the most. However, I have a strong desire to move towards using the FT736R only. 


Tuesday, September 22, 2020

QO-100 Analogue Ground Station

Yes, it can be done. One can use a fully analogue ground station for QO-100 operations.

My first attempt included a Yaesu FT-290R2 for reception, along a Yeasu FT-817 for transmission on 70cm. Once a TX frequency has been established, following the drift of the LNB was an OK-ish task during QSOs. Changing frequencies was an unpleasant juggle of setting the receive frequency and trying to find the transmit frequency without annoying everybody else of the transponder. This ballet is performed with VFO controls of two different radios.

Second attempt: Yaesu FT-736R, the satellite machine from the past. It was doing great, in particular when changing frequencies, using the satellite mode. However, my cheap LNB kept drifting in sunlight, while the up-link converter stayed rock-solid. Hence, using the FT-736R was a constant switching between SAT-mode and RX-QRG. Once a frequency was established, TX-QRG needed to be adjusted. I am not sure how many actuations the little SAT-switch can take. What I am concerned, it took a lot of focusing in order to not adjust the VFO in the wrong setting, thereby messing up the RX/TX-offset.
With a stabilized LNB, this might be a different story.
I liked the possibility to use the VFO-knob to scan up and down over the band, knowing that, whenever I pushed the PTT, the frequency would be at least close.

The FT-736R is back in its box for now. In terms of having contacts, the SDR-option seems a lot more convenient, in particular when locking the reception to the satellite's beacon. Transmission is stable enough, in my experience, so nothing to be bothered about.
As an added bonus of the SDR solution of the analogue way, there is signal processing available when using a computer for reception. 

Further, I tried to use a Yaesu FT-790R2 as baseband up-link transmitter. It did work. However, there are two observations to share: 1) some weird spurious transmission were visible in A1A, 2) the audio in J3E was OK but not punchy at all.

Consequently, I will be using the Yaesu FT-817 as a baseband TX and the SDR receive setup, for the time being.


Saturday, August 29, 2020

QO-100 A1A up-link idea

This is something I had in mind for quite some time by now. What about an A1A only up-link for QO-100?

This is an old idea. At the time, this idea was to create a CW transmitter for 70cm based of a 2m signal. I have seen similar attempts to get something transmitting on 3cm. So, why not on 13cm?

Having done some "maths", I came up with a carrier of 96MHz, which is available as a regular crystal.

With a factor of 25, this will result in a 2.4GHz frequency.

Now, why is that interesting? The multiplication of 25 can be achieved with 5 x 5 .... dahhhh. Yes, sounds simple enough. Here is the interesting thing, it should be easy with a square-wave oscillator to generate 480MHz. At this frequency, it is pretty easy to build a strip-line filter or cavity resonator to clean the signal. Now, we just have to multiply the signal again. So, we might want to use a non-linear amplifier again, in order to create all the wonderful harmonics. Again, a 2.4GHz resonator should not be to hard to build.
And here is the idea. What if we used a rather high powered amplifier at 480MHz, which is easy to build, and a non-linear element to generate all those harmonics at decent power.

With a VTCXO of 96MHz, slightly pulled by a few kHz, one should be easily creating a signal in the CW band of QO-100, using the above mentioned method.


QO-100 Up-link update

 The last few days have seen a little bit of modification and optimization to my setup. Mainly, the shortening of the helix feed. While I was monitoring my A1A signal on the downlink, I gradually cut windings of the the uplink helix. I was not sure if I could see any difference in signal strength, to be honest. Anyway, I ended up with this:

Downlink (left) and Uplink (right)
The dishes are ducked down for a reason. This is my roof deck, we often experience heavy winds in the Netherlands. With the dishes sitting low, weighted down, the positions will be stable over the course of the year.

Presently, the UL uses 10m of RG-6 cable, the original one with the hollow dielectric. This length is certainly not ideal. In the near future, I will build an outdoor unit, sitting next to the UL feed, housing the converter and the PA. This should improve my signal by some dB.

For the time being, all I heard was that my signal could be stronger, but was fine to copy... what more do you want?

73!


Tuesday, August 25, 2020

SDR and the DJ-Tech DJ-Mouse

Here is what you have missed, if you are not in the world of DJs.
The DJ-Tech Mouse, which employs a super-nice big wheel in the center. Have a look:
https://djtechtools.com/2009/08/20/the-dj-mouse/

Guess what this wheel can be used for in any random SDR software.... a VFO.


QO-100 ground station update

My previous post show tons of opportunities for improvement. The more I was thinking about those, the closer I came to my initial gut feel, i.e. using a helix as a feed for the up-link dish.
In fact, the helix was sitting on my desk for quite some time by now. I had doubts how to mount the helix in the first place, also matching appeared to be a big deal, without the help of any decent GHz-capable measurement equipment.

However, seen that no matter what I did, I could not really improve the performance of the up-link. Essentially, I spent two entire night to find the best position of the dish. (Night-time, so nobody is on the satellite, avoiding to disturb more senior users)

When listening to traffic on Es'hail 2, I often heard that operators switched from patch feeds to helical feeds for their up-links and reported better results with those. Was my gut feeling correct?!

So, today, I returned to trusting my gut feeling. So I removed the patch from the weird reflector / holder shown in the last post. I used a small piece of PCB to form a base, essentially a mount, for the helix. Yes, I could pretend that this was a carefully calculated matching strip for matching my 75Ohm SatTV cable to the helix, but it wasn't. I dimensioned and adjusted the PCB just such that the helix would be - more or less - in the center of the reflector.
note the remainders of glue where the patch was

Feel free to count the turns, which would result in a little of 6. My idea was, that I could always cut some off. It is much harder to cut wire on ;-)

The photo shows, it is night-time again. So, why not firing up the station and do some test transmissions?
And how right was my gut?!

lower beacon at 69dBuV

What a difference! My signal is now just 9dB weaker than the lower beacon!
Of course I had to do some side-band test. And yes, now I think I am QSO worthy.

The present setup still employs the "attenuator" made of about 10m of 70Ohm SatTV cable. So, as long as I still have not yet figured out how to build an outdoor unit (PSU,TX-converter and PA in a weather-proof box), I still will be able to do one or the other QSO.


Friday, August 21, 2020

QO-100 Es'hail-2 ground station

It has been a while since I was busy with a ground station for the geosynchronous (geostationary) satellite Es'hail-2 also known as Qatar Oscar 100 or QO-100.

The major delay in the beginning of the project was to receive an assortment of coax adapters. Finally, those were in, now, the down-link was sorted rather quickly. There was a disused 40cm dish, which I used to analog ASTRA reception. When ASTRA satellites turned digital, I lost interest in watching those, so I never upgraded the equipment. Although, I never dumped any of that stuff either.

So, here was my down-link receiver, PLL-LNB with the old 40cm dish in a FUNcube SDR dongle. That worked perfectly. I later replaced the FUNcube dingle with an SDRplay RSP1A, so that I could receive the entire bandwidth of QO-100's narrow band transponder, allowing for locking on the mid-beacon for frequency stabilization.

Concerning the up-link, I decided to go for a DXpatrol converter. I like the possibility to select the baseband, although, I will probably stick with 432MHz.
To amplify the 2.4GHz signal, I went for the omni-present chinese 8W WiFi-PA.

Then came a long struggle of what to do about the up-link hardware.
Initially, I considered an RHCP helical antenna, something in the realm of 15 to 20 turns.
Then I found a 70cm offset dish in the trash. So, what about a 4 to 6 turn LHCP feeding helix? And yes, I wound that thing. But, the mechanical details of holding the thing in place put me off again.
Finally, I decided on a K3TX LHCP patch feed for the 70cm dish. 
I know, 70cm is rather small for a 13cm wavelengnth... 10 lambda upwards make the deal... I know. However, 70cm is what I got.

The dish I got had not LNB/feed mounting hardware, so this is what I came up with.

K3TZ LHCP patch, PCB over Al

You may wonder what the strange structure to the left is, this will be the mount to the dish.
Something not obvious from the above picture, I am using a F-connector for this feed.
Please note that this picture was taken before I filed down the edges to of the reflector to the circle seen scratched into the aluminium sheet.

The patch feed added to the up-link dish

Winds can be pretty strong over here, so I mounted the dish to a concrete parasol stand.


Up-link (grey) and down-link (white)

Note that both channels are using 75Ohms satellite cable. While for the down-link this is fine, the up-link will experience this as an attenuator, in particular over the length I am using for this experimental setup (about 20m).

Having done some experiments, I could hear my signals in both CW and SSB (USB). While CW was easy, single side band was somewhat challenging. I would not count for any SSB QSO with the attenuator in place.
However, CW should be just fine. Have a look how the signal compares to the lower beacon:

Lower beacon and pa1gsj carrier

This was my first day of bouncing signals from QO-100. I know what I need to do now, i.e. building an outdoors cabinet next to the up-link dish.

I hope to be QRV as an audible station on Es'hail-2 soon.


Update

After further improvements, I can now provide relative signal strengths from my receive setup:

  • transponder noise about 32 dBuV
  • CW beacon 58 dBuV
  • my own signal 41 dBuV
I can also report that I made two CW contacts by now, the lower report was 589. 

Thursday, May 14, 2020

Boom boom pafffff

Something totally off topic today, OK, it's audio, no electronics involved however.

IKEA is known for some interesting projects here and there, beyond the famous bookshelf. Lately, they introduced a product range which appears to be a collection of random stuff, the collection being "FREKVENS". There are even products that could be interesting for a blog concerned with electronics. No worries, I wont be writing about a silver rain coat or a silver cushion cover either.
Let's have a closer look at the only real IKEA flat pack product in the collections, the FREKVENS Cajón (drum).
No, this is not a drum, this is a cajón, and instrument well known in Spanish and Afro-Cuban music. A cajón can create sounds similar to various parts of a drum kit, which is a matter of great skill, which I don't have.
There are a few more things wrong in the product listing, at least what the images are concerned. The side with the big whole is the back-side (or reverse, depending on your style of English). Hence, the guy in the photo sits on it the wrong way. Also, he appears to be slapping the sides of the instrument, which are made of much thicker material and not supposed to be the main playing surface.

Anyways, I bought one of those flat-pack instrument kits and build it according to the provided instructions. BIG mistake! The more I learn about the instrument, the more obvious this should have been.
The assembly instructions take a similar order to something like a nightstand. Which, seen from IKEA's perspective, does make sense. However, when following the leaflet, it is almost inevitable to create a misaligned box  that does not sound right.

Step 1
The instructions start with mounting the snares to the (front of the) bottom-plate, so far so good.

Step 2
The side-walls are screwed to the bottom-plate. This is the first instance where things can go wrong. The alignment of the outer edges of bottom-plate and side-walls needs to be precise. This might not be that important on the bottom-plate, desirable however.

Steps 3 and 4
According to the instructions, the top-plate is now mounted to the side walls, very similar to bookshelves, nightstands,  etc. I cannot emphasize enough, don't do this yet. I did it and I ended up with a slightly misaligned top-plate. This misalignment kills the instrument!

Step 5
In this step, the playing surface, i.e. the front, is mounted. Remember, the front is where the snares are. This is very important for the functioning of the instrument and not clear from the instructions.
This step should be done after step 2, if not before...
If you followed up to now, you will understand that it is important to not tie down any of those screws yet.

Step 6
Here, the back-plate of the cajón is screwed to what we assembled so far. Please note, we skipped steps 3 and 4, so there wont be any (I should have written about that in step 5, sorry!).

Final assembly according to me
If you followed my advice, you skipped steps 3 and 4. What you should have by now should be a square wobbly bucket with no lid.
At this stage, carefully work the top-plate into its position. This might be a bit tricky, therefore, we did not tighten those screws. Once the top-plate is in place, we want to first tighten the screws of the front-plate including the ones we skipped. This will auto-align the top-plate to the side-walls. This alignment is most important to the good functioning of the instrument.
Once this alignment is established, screw down and tighten the 2 front screws on the top and the side-walls.
Now apply all the remaining screws. And tighten all screws on the back and the lower half of the screws on the front.

Tune up
In case of all screws being tight, you will have to hit the cajón very hard to get the snare effect. This will result in an imbalance between the snare and the bass drum sounds.
Therefore, what you are looking for is a small gap between the top-plate and the front-plate. To realize a somewhat even gap to your liking, you have 5 screws in the top half of the front-plate to play with, i.e. loosen and tighten. Every little bit of tension here and there will change the tone and snare sound created by the cajón. It took me a while to balance the right and left corners of the upper playing surface.

Conclusion
IKEA is good in creating wooden flap-pack products. The FREKVENS Cajón is no exception, when built and aligned correctly.
There are competing products available from musical instruments suppliers, here is an example. This example supposedly requires additional materials for assembly, although at a lower price.
What I am concerned, after having aligned my cajón, I am pretty happy with the sounds it can create and look forward to learning this instrument.