Wednesday, 29 January 2014

LNA4HF Review


Affordable, portable and works, this is a must-have for upconverter owners and shortwave listeners.

What is it? 


The LNA4HF is a low-noise amplifier (also called signal booster) for long -, medium -, and shortwave reception, amplifies signals 80 - 100 times between 0.15 MHz and 30 MHz. 
It will let you hear more signals with your RTL-SDR plus Ham-It-Up setup, and can be also used for standalone receivers.

How much?

Costs 27 USD / 20 EUR / 16 GBP including shipping, available from Adam, the manufacturer via his webpage. You pay for the item when it arrives, no shipping worries.
Disclosure: I received my sample for free for testing. Thanks. This is the second product I receive from the manufacturer, and like before, no instructions nor "please write this". Adam simply answered my emails and updated his product blog with answers to my questions. 

Size and power


Measures 25x25 mm, or one square inch. Small enough to be placed in an electrical box. 
Signal connectors are SMA female. 
Wide range of power options:
1) 6-12 V via supplied red and black cable. 
2) 5V supply by soldering a piece of wire onto the board, so power from the the Ham-It-Up can be used. This is great for those who wish to install the LNA in an enclosure, close to the upconverter.
3) 13.8 V (car battery), place a 470 Ohm resistor in line on the red (positive) cable. 

Fine tip solder and advanced soldering skills needed for 5V modification (components are the size of an ant's head), 470 Ohm resistor costs around a dollar.
I simply used six AA batteries in a cardboard tube, taped wires to batteries, and ran them to the board power supply.
After providing power to its brother, the LNA4ALL with screws, seeing chunky red and black wires
in the bubble wrap envelope was a relief.

Low-pass filter


Interference from signals above 30 MHz (Broadcast radio etc) are reduced due to a low-pass filter at the antenna input. The bypass switch will be rendered useless on the Ham It Up - no signals above 30 MHz, shortwave only.
Tested efficiency by tuning to strongest boadcast station, gain up to 42.1 dB, LNA4HF made an audible and visible difference when inserted into the signal chain.
Disable the low pass filter and get a preamp covering 0.15 Mhz - 2000 MHz by cutting the electrical connection as per Adam's instructions, as I already bought a preamp for VHF (and hate to solder) it's not tested.


Placement



Preamps should be placed right after the antenna for optimum performance, so electrical noise picked up by antenna cable will not be amplified any further. In theory. Daily practice is to place any preamp indoors, where I can easily provide power and won't have to worry about waterproofing. 
A cheap and cheerful solution is to place the preamp and power supply in an electrical junction box, add a switch for On/Off, place the preamp right at the antenna, and turn on power when you need it. This is a tried and tested solution with a 9V battery for field trips and / or maximum performance.

Performance


Works as advertised, signal height is 20 dB higher in SDRSharp. Audible difference.
Tested on four shortwave frequencies with an outdoor discone, same settings in SDRSharp, only removing the LNA4HF for comparison.
Beginner setup, no elaborate noise reduction measures, only a modded USB cable connecting a R820T stick, pigtails between Ham-It-Up and LNA4HF, 10 foot coax to discone. Urban location with significant FM, pager and UHF interference.




Utilizing the performance potential can be only achieved with an optimized antenna system - a proper shortwave antenna and noise reduction measures will make a huge difference.
Still, even with this VERY basic setup the improvement is clearly there.


Using with standalone receivers



Shortwave aficionados will love this preamp - the low pass filter reduces local interference whilst simultaneously amplifies signals.
An Icom IC-R5 (handheld wideband receiver, about 70-80 USD on eBay used) easily received the same stations used for testing the LNA with an upconvrter - why not connect the preamp to the Icom?
Connecting the preamp between the antenna and the receiver resulted in better signal quality - see video below. Same antenna and same volume settings, Band Scan.


Note 1: the shortwave receiver and antenna above is a far cry from a dedicated shortwave receiver and proper antenna, included here for comparison purposes only.
Note 2: video above with a discone, a longwire plus preamp will possibly overload and damage an Icom IC-R5, this hasn't been tested.

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