Posts by PA3FYM

IW9EZO said "Probable not precise, I'm new in the measures."

OK, taking the risk I'm telling nothing new, perhaps a 'short cut' advise (assuming the directional coupler is ok):

- Leave sweep output on 0 dBm (1 mW)

- Disconnect the directional coupler from the antenna

- Place a proper 50Ω load as 'antenna'

- Measure the response at 2400 MHz

(if it's a good 50Ω load you should see a (very) low response)

- Disconnect the load

- Measure the response at 2400 MHz

(should be maximum because all power is reflected)

(normally one should also make a short, but I leave that out ; -)

Now you have the difference between an 'ideal' 50Ω load and no load.

- Connect the antenna and measure the level at 2400 MHz.

The RL Is the difference between the level of the 'open situation' and the level you measure with the helix.

To see if there is a 'dip' try to increase the span to e.g. 1000 MHz

IW9EZO Can you make a photo with helix disconnected and plot with helix connected?

DB2OS: That's exactly what I said: "Having said that, of course the 'turn key' solution in a casing, ready to be mounted in a standard satellite dish, is invaluable ; -)"

I8LYL former I0LYL : OK, sorry I misunderstood. Rule of thumb is 1 turn per 0.1 'dish f/D'. So a dish with f/D = 0.5 needs 5 turns, a (standard broadcast) offset dish with f/D = 0.7 needs .... eh ... 7 turns ; -)

C'mon guys, helices are known for ages, so it's (at least) peculiar 'we' are reinventing/questioning them from here. Google is your friend.

I8LYL former I0LYL : No, that helix is not the same as G8HAJ's backfire helix.

The 'winklerantennebau.de' is just a normal helix with a different approach to match the Zo ~120 (+j0) Ω to 50 (+j0) Ω. Nothing special and could be made with scrap materials for a few euro's. Having said that, of course the 'turn key' solution in a casing, ready to be mounted in a standard satellite dish, is invaluable ; -) This makes it that the price is 38 euro's (iirc) .

Just to make a statement (I posted this pic earlier in this thread, appealing to the NIH (not invented here) feelings .... nothing new (old skool!):

Of course, feel free to reinvent the wheel ; -)

When you transmit RHCP and bounce against a passive reflector (the moon) then the signal returning to Earth will be LHCP. Popular feed designs for EME are e.g. 'septum' feeds OK1DFC for example). One feed, two polarisations (on different terminals). If the backfire helix has this feature, I don't know.

G8HAJ : interesting! I read your blog post, and you were not sure whether you made a RHCP or LHCP feed. But I saw you also have a 23cm RX station.

If I remember correctly for EME uplink is RHCP, so the reflections are LHCP.
Assuming your 23cm RX-station works it must be able to conclude whether you made the right polarisation for 13cm?

The worst case is -3 dB ; -) But nowadays 'gain is cheap' (c) W1GHZ

DB8TF : read FreeNode IRC channel #es'hail-2

Well ... this power regulation has everything to do with the capabilities and QoS (Quality of Service) of the transponder per user requirements. So .. I reckon it's not (too) off topic ; -)

And yes, from what I've seen concerning transponder noise and (illicit) signals, I fully agree, Melco did a good job!

I believe like that, but now imagine you've 100 signals (in 100 'channels') and each signal/channel wants its own protection/quality/comfort.

That means considerable efforts on the linearity of the transponder/amplifier/contraption to avoid 'in band' IM (so that not another user suffers from your IM). It's not only with satellites but also with mobile telephony, so the 'handy' you are using.

About NPR, this is a nice publication: https://www.lintech.com/PDF/npr_wp.pdf

Output Back-Off. In my own words: the full capabilities of the TWTA will not be used but (in this case) output is 6 dB down. This is to improve linearity and improve NPR (Noise Power Ratio), so that in the passband there will be less IM (intermodulation) due to other (different) modes and users (very briefly said).

So, O/P of the HPA (TWTA) is 100W (50 dBm) - 6 dB (OBO) = 44 dBm - 1.5 dB losses = 42.5 dBm + 17 dBi (EC horn) = 59.5 dBm (= 29.5 dBW).

Divide this into 50 channels (however ... 50 x 2.5 kHz = 125 kHz) <-- ?

But say ... 50 x 5 kHz channels you've 29.5 - 10log(50) = 12.5 dBW per channel.

The rest follows from the sheet.

Like Elon Musk said: "Ignore the noise, focus on the signal"

I8LYL former I0LYL : I'll try to verify that. So hopefully 'the silence' is gone in February ; -)

Well, AMSAT-UK based this on an ITU-lecture, given by Es'hailSat in Prague in 2015.

See: http://www.itu.int/en/ITU-R/sp…resentations/Eshail-2.pdf

or ... https://www.qsl.net/zs6bte/Sat…ellite_files/image002.jpg

To word it in another way: reading the ITU-presentation of Es'hailSat concerning the user requirements Melco was assigned the task to build transponders complying with these requirements.

Thus, if 100 channels of 2.5 kHz are occupied with 100 users, and each user generates 20 dB SNR (inside 2.5 kHz) with 5 - 10W RF and -say- 20 -23 dB dish gain (50 - 75cm) , it's enough (?)

Flo, I think pe1chl tries to make another point. For an active NB-transponder usage it is by far not necessary to have a moonbounce capable uplink. Last Sunday during the Microwave Meeting in Heelweg (Holland) a friend of mine stated: 'They have EME stations for 13cm , but we never hear them?' ; -)

In Lyngsat (this afternoon) the reported channels by I8LYL former I0LYL were attributed to BADR-7 (iirc) on Jan 23th

Since December 28th last year an IRC (Internet Relay Chat) channel was created on the FreeNode network.
Channel name is #es'hail-2 . If you don't have an IRC client you can use the (very good) web interface http://webchat.freenode.net See screenshot below and of course press the Connect button : -)