Jump to content

Banner.jpg.b89429c566825f6ab32bcafbada449c9.jpg

Looking to get a DC Power Inserter for my radio telescope

Coto

By Coto
in Radio Astronomy and Spectroscopy

Recommended Posts

Coto

Coto

Posted
Posted

Hi,

 

I just got my Ku-Band LNB (https://stokostos.gr/tv-sat/lnb/signle/single-eco-slim-lnb-amiko-l108.html), dish & my SDR (HackRF One). There's just one thing stopping me from getting to work with my homemade radio telescope:

How do I provide power to the LNB? I've heard I need some sort of a 12V DC Power Inserter of some sort, which brings more questions: Why 12V? Would more be better? And where can I find such electronics? Do they go by a different name? Would I need any adapter to connect the power inserter to the HackRF?

Link to comment
Share on other sites
  • Replies 39
  • Created
  • Last Reply
Tomatobro

Tomatobro

Posted
Posted

Hi Coto

The LNB polarisation is switched by the input voltage.  See in the specifications Polarity Switching Voltage: Horizontal: 16-18V / Vertical: 12-14.5V

However, my experience is to keep the applied voltage as low as possible and if you need to change the polarisation then just rotate the LNB in the bracket.

LNB's have internal heaters so let them warm up for half an hour 

For power you can build your own inserter. Capacitors block DC but allow AC to pass through so what is required is to insert a capacitor in the centre coax feed. A small choke on the supply input kills off any noise.

You only need one inserter which goes between the receiver and the LNB.

 

20180814_140310.jpg

Link to comment
Share on other sites
symmetal

symmetal

Posted
Posted

The LNB you've selected is normally used for satellite TV reception so the DC voltage you supply will determine what polarization signal you wish to receive. 12.5V to 14.5V for vertical polarization and 15V to 18V for horizontal polarization. Outside these voltages it won't function properly and above 20V will likely damage the LNB.

Alan

Ah! Tomato beat me to it. ?

Link to comment
Share on other sites
Coto

Coto

Posted
  • Author
Posted

@Tomatobro: I'm having a hard time finding a Bias Tee supplier near me, so I think my best bet is to actually build one myself.

Do you have a tutorial on how to do that? Or just tell me what parts I need to get and give me a circuit diagram to look into it. Any more adapters needed to connect it to my HackRF? And would I have more gain with another SDR, or does the given power solely depend on the Bias Tee and not the SDR?

Also, why is that:

4 minutes ago, Tomatobro said:

However, my experience is to keep the applied voltage as low as possible

 

Link to comment
Share on other sites
Tomatobro

Tomatobro

Posted
Posted

Coto, if you are just starting out then you might be better off using a Sat finder as these are very cheap. These can be modified to give a dc output that can be measured and recorded using a cheap digital voltmeter. Detecting the Sun with one of these can be fun (its how I started). If you need more details on how to do this  let me know

Link to comment
Share on other sites
Tomatobro

Tomatobro

Posted
Posted
6 minutes ago, Coto said:

@Tomatobro: I'm having a hard time finding a Bias Tee supplier near me, so I think my best bet is to actually build one myself.

Do you have a tutorial on how to do that? Or just tell me what parts I need to get and give me a circuit diagram to look into it. Any more adapters needed to connect it to my HackRF? And would I have more gain with another SDR, or does the given power solely depend on the Bias Tee and not the SDR?

Also, why is that:

 

You are trying to measure very VERY small changes in signal level. Higher voltages make more "noise" and so you want to keep everything as stable as possible

I do not know anything about what dish size you will use or what objects you want to record. The Sun is an easy target to start with so I would go with that.  Inline pre amps will get you a reflected signal from a full Moon. But anything else requires dedicated antenna's (for say the Hydrogen line).

Link to comment
Share on other sites
robin_astro

robin_astro

Posted
Posted
27 minutes ago, Tomatobro said:

Inline pre amps will get you a reflected signal from a full Moon.

The moon should be detectable with just a sat finder and a modest sized dish.  See my tests here for example.

http://www.threehillsobservatory.co.uk/astro/radio_astronomy/radio_astronomy_1.htm

(The phase of the moon does not make much difference at this wavelength as it is the heat radiation from the surface we are picking up, not the reflected sunlight, though it is obviously easier to aim the dish if you can see the target  !)

The biggest problem I found with this simple setup was stability rather than detectability above the noise. If I could have cracked this I believe the stronger galactic sources might have been detectable

Robin

Link to comment
Share on other sites
Coto

Coto

Posted
  • Author
Posted

@Tomatobro: I'm not a beginner in radio astronomy (I've actually been using the Green Bank 20m Radio Telescope and made tons of successful observations (I should post them on this forum soon)), however my electrical engineering is limited, and making my own radio telescope from scratch would require knowledge & experience beyond astronomy, so I would prefer to get some detail instead of just boolean results like whether the sun emits radiation at equivalent wavelengths or not.

I'll try to recreate what you've presented on the diagram and let you know if I've got any questions.

As @robin_astro said, the moon emits electromagnetic radiation due to thermal emission, rather than reflecting EM waves from the sun.

Speaking of lunar's thermal radiation, I actually produced this false-color radio-"image" of the (near) full moon with the 20m [at 1800MHz - 4 polarization channels averaged], overlaid on an optical image (rotation is adjusted properly). I've also observed the (near) new moon, which allows us to detect Δflux (the difference between the flux density on a full vs new moon), however I need to do some data-analysis before presenting the final "image".

final.png

(The red glow offset is due to the telescope's limited beamwidth).

Link to comment
Share on other sites
Carl Reade

Carl Reade

Posted
Posted
1 hour ago, Coto said:

So, apparently there are various Bias Tees on ebay and amazon, but almost all of them come with SMA ports... What connectors etc. would I need to connect these to my LNB and my HackRF?

The one I got is f connector the same as LNBs. I added a small f lead and an f female to SMA male adaptor. On the antenna side added an f barrel.IMG_20180820_210438.thumb.jpg.1d6b9ebfcbdecbfd71b84d896a21a3b3.jpg

Link to comment
Share on other sites
robin_astro

robin_astro

Posted
Posted

It is designed for use with a conventional antenna and separate power supply so unlikely it will supply any DC at the signal input (or feed any through)

Robin

EDIT:  I see it can be powered using DC on the signal output coax so I suppose it is possible it will insert the DC at the signal input from a separate supply.  Easy to power it up and check for DC on the input 

Link to comment
Share on other sites
Coto

Coto

Posted
  • Author
Posted
12 minutes ago, robin_astro said:

EDIT:  I see it can be powered using DC on the signal output coax so I suppose it is possible it will insert the DC at the signal input from a separate supply.  Easy to power it up and check for DC on the input 

Okay, what does that mean? What do I need to do to check if the LNA is capable of replacing a Bias Tee?

Link to comment
Share on other sites
robin_astro

robin_astro

Posted
Posted
32 minutes ago, Coto said:

Okay, what does that mean? What do I need to do to check if the LNA is capable of replacing a Bias Tee?

apply power via the board connections (at the voltage the LNB needs eg 17V) and use a meter to measure the DC voltage at the input coax socket. If it is 17V you are in business

Link to comment
Share on other sites
Coto

Coto

Posted
  • Author
Posted
37 minutes ago, robin_astro said:

apply power via the board connections (at the voltage the LNB needs eg 17V) and use a meter to measure the DC voltage at the input coax socket. If it is 17V you are in business

I'm supplying the LNA with around 9 or 10V. I attach the Voltmeter to the OUT SMA port (only 0.24V...):

image.jpg

image.jpg

(Attaching the voltmeter to ANT SMA port:)

image.jpg

Am I doing something wrong?

Link to comment
Share on other sites
Carl Reade

Carl Reade

Posted
Posted
59 minutes ago, Coto said:

I'm supplying the LNA with around 9 or 10V. I attach the Voltmeter to the OUT SMA port (only 0.24V...):

image.jpg

image.jpg

(Attaching the voltmeter to ANT SMA port:)

image.jpg

Am I doing something wrong?

Looks like it's not got a bias tee configuration. The specs say it can take the voltage via the receiver side (phantom) but then you will need a bias tee to feed it anyway.

On another note you can run the LNB on 13v possibly 12.

 

IMG_20180821_191312.jpg

Link to comment
Share on other sites
robin_astro

robin_astro

Posted
Posted
19 hours ago, Carl Reade said:

Looks like it's not got a bias tee configuration. The specs say it can take the voltage via the receiver side (phantom) but then you will need a bias tee to feed it anyway.

Yep, looks like you are out of luck.  BTW take care before injecting the DC for the LNB that the HackRF is going to be happy with that or isolate it from the DC. It might not like it. Best check with the supplier/forums.   (I dont know the HackRF but it might be worthwhile checking if it has a facility for putting  DC power on the coax to power the LNA and LNB. This is how it is done in satellite receivers. )

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.