Suggestion on LNA

SatNOGS Hardware
1

Hi everyone,

I’m trying to improve my SNR.
I found this cheap LNA online.

someone already tried?
Any feedback?

thanks in advance!

2

I have no experience with such wideband preamplifiers.

But in general, I would ask at least the following questions.

  • indoor or outdoor use?
  • power feed: via coax cable or separate line?
  • for RX only or also TX?
  • in case of TX: switching via HF or PTT?

For 430 - 440 MHz I’m using the VV 435 VOX from SHF Elektronik.
And for 144 - 146 MHz the equivalent one.

3

to answer to you:

  1. Antenna is outside, but most likely (as it is now) the rasperri pi and the LNA might be inside.
  2. I’m not an expert in cabling, but I think is aSMA connector. the cable itself might be coaxial
  3. only RX
4

Good morning,
few questions:

  • what is the distance from antenna to SDR ?
  • what coaxial cable you are using ?
    You have to pay attention to coaxial cable type and lenght. For example, for RG174 (wich is the most common cable matching with SMA connectors), you have 6.2 db attenuation for 10 meters lenght.
    So, best advice, you have to mount the LNA right under antenna, with the shortest coaxial cable you can. But outside, you have to find a weatherproof case and put the LNA inside.
    After that, you shall know if you need also a filter after the LNA.
    I dont know what schema is inside the LNA RF Amplifier Module, but if inside is a TQP3M9037 chip, its OK for this low price.
    Cristian - YO4DFT
5

I currently have 5 of them in use. Low noise, as advertised, but I use all 5 of them behind a bandpass filter for the wanted frequency. So, 403, 435, 1550 , 2250 MHz and one running with highpass filter 1400 MHz and up.

2 Likes
6

Answer your questions:

  1. the cable run for 3.60m.
  2. I’ve found these specs:
    Includes 1x RTL-SDR Blog brand V4 R828D RTL2832U 1PPM TCXO HF Bias Tee SMA Dongle, 1x portable multipurpose dipole antenna set. Dipole set includes 1x dipole base with 60cm RG174, 2x 23cm to 1m telescopic antenna, 2x 5cm to 13cm telescopic antenna, 1x 3m RG173 extension cable, 1x flex tripod mount, 1x suction cup mount.

I think I can put the LNA between the RG174 and the extension 3m cable no?

the scheme inside… I’m not sure… I just bought it from here

7

Ah… so another filter? any suggestions or references?

I’m going to check your waterfalls :smiley:
Are you happy with this setup?

I’m new sorry… Trying to learn!

8

Sorry, I remember, you have V antenna on balcony. OK, its a short cable.
In your situation, you shall have more success if you will use another antenna with some gain. As I remember the photo, I suppose you can use a 3 elements Yagi (but in this case you shall receive in good condition only the one band, VHF or UHF), or a double bi-quad (like I am using now). The bi-quad is wide band, you can use it from 400 - 440 Mhz, for receptions.
It depends what can you put on balcony, without metals in front of antenna.

Cristian - YO4DFT
station 3600

9

If you want, I can describe for you how you can build in 60 minutes a bi-quad antenna for UHF. You need 2 meters of Cu wire, 3-4 mm diameter, a piece of hard cardboard, possibly from a packaging box, 60 x 40 cm and a roll of self-adhesive aluminum foil, used in construction.

Cristian - YO4DFT

1 Like
10

There are some nice DK7ZB designs, have a look this one for example.

Place at a 45 degree angle from your balcony.

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11

“another filter” ?
At this moment it’s not completely clear to me for which frequency range you try to improve your SNR. Is it regular radio reception, or for use on a satnogs RX station. If the latest, which frequency range do you plan on for reception. A bandpass filter can be some 434 MHz SAW filter from Alie (I use 2 of those) but with that filter no reception outside the 430 - 440 MHz range is possible. With the antenna’s from the kit you linked to I would indeed suggest to improve the antenna side before adding any preamp.

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