FX-4 QRP Transceiver - A little cutie!

This is the amazing little FX-4 5-Watt SSB and CW ham radio transceiver from LnR Precisaion in the US.

I had placed myself on LnR Precision's waiting list for people interested in buying this little rig when it was finally ready for market, and placed my order immediately I got the go-ahead from the company at the end of February.

The LNR FX-4 is a gorgeous little back-packable Ham radio that covers four popular Amateur Radio bands, 40m, 30m, 20m and 17m. Those are licensed Ham Radio frequencies on the 7 MHz, 10 MHz, 14 MHz and 18 MHz HF bands (aka "short-wave" bands), which should make this little rig appear to bushwalkers, hikers, campers, and SOTA (Summits On The Air) enthusiasts everywhere.

Like many QRP (low-power) ham radios, this 5-Watt single-sideband and morse code rig uses a BNC connector for its antenna. The BNC is on the left, together with a power socket for 12v DC power (center positive). On the right side of the rig there are 3.5mm (1/8th inch) stereo sockets for the microphone (included), earphone and Morse key. The mic plugs straight in with a 3-connector plug, but you will - of course - need to provide your own morse key or paddle, and a set of headphones (or ordinary stereo ear buds). The audio output is enough to drive a small 1-watt loudspeaker, so it would a good idea to take a small mobile loudspeaker with you if you plan on demonstrating the transceiver to any interested onlookers at, for example, a JOTA event with the Scouts.

The LNR FX-4 trail friendly radio just needs a resonant antenna for the HF bands you plan on using, or you can use a small antenna tuning unit (ATU) of some kind with a suitable length of wire. At low power you really do need a full-sized vertical with radials or a half-wave antenna. A smaller antenna will waste too much of your 5 watts as heat, making it even harder for people to hear you.

I have already made up and pre-tuned a 4-band SOTA-type link dipole for 17, 20, 30 and 40m that uses crocodile clips to make or break the two sides of the dipole to they resonate at the correct frequencies. It is designed to be hung up on my 20-foot squid pole as an inverted-vee antenna. (I believe these fishing poles are referred to as "crappie poles" in the USA.) When I slide my dipole centre connector down to the base of the top (thinnest) section of the pole, the height there would be closer to 17 feet. But for SOTA and lightweight portable ops, that should still be fine. A 33-foot (10-meter) pole might get out a wee bit better, but then it's a lot bigger to carry around on a steep hike!

Someone asked me how much electric current it consumes, and the manual tells me it drains 1.2 amps on transmit and between 250 to 270 mA on receive. It has an adjustable side-tone pitch for CW (morse code) enthusiasts from 550 Hz to 1.5 kHz. I used the inbuilt menu function to set it to 750 Hz, and to program in my callsign - VK2DMH. The radio then uses this for its inbuilt morse code CQ function, which is triggered by pressing down on the volume control. The FX-4 also has a built-in keyer that can send perfect code at speeds from a lazy 5 wpm up to a blistering 50 wpm once you plug in an Iambic paddle.

One thing I really like about it is that the CQ function works fine even if I am using a manual Morse key. (My little Chinese HB-IB CW-only rig will only send its CQ automatically if I have a paddle plugged into it.) I can also reverse the paddle connections if I need to via the FX-4 menu. That is a lot quicker than rewiring a cable.

As for its built-in DSP filtering, the LNR FX-4 allows me to select 300, 500 or 1300 Hz bandwidths for Morse, and 1600, 1900, 2200 or 2500 Hz wide for SSB voice signals.

The FX-4 does not have full QSK (ability to listen between sending CW characters), however the CW delay is adjustable between 0.1 seconds and 1.5 seconds. To me 1/10th of a second seems pretty good.

The radio's receiver sensitivity is 0.3 uV and its spurious emissions are -43 dB at 5 Watts. It has 40 memories to store your favorite frequencies, that's 10 channels than can be saved for each of the 4 bands. It also has high VSWR protection built-in, and the when you hold down the key to transmit, the LCD display has little bar-graphs for both forward and reflected power out. It's not your usual kind of SWR meter, but it lets you know if your antenna is out of whack.

One thing I do not like about the FX-4 is it's SSB noise blanker. I found it to be of no help to me whatsoever, as it took a slightly noisy signal and made it quite unintelligible. With the noise blanker on the signal sounded like it was being blown through a stream of air bubbles from a deep tank of water! Oh dear!

Anyway, guys. If you want to know more about it, then you can read the manual! Just click the link. And no, I don't get a commission for sending you there. I just happen to like this little radio. Okay?

My homebrew SOTA type 4-band link dipole to suit my LnR Precision FX-4 transceiver. By opening or closing the pairs of crocodile clips, I can have my inverted-vee antenna resonant exactly on the band centers on 18 MHz, 14 MHz, 10 MHz or 7 Mhz - and I don't need any ATU. The 10m length of RG-174 coax is directly soldered to the center of the dipole and waterproofed.