Doesn't everyone hate Micro-USB?? Wouldn't we all love to have just one type of USB connector? Well I would for sure. I think that USB-C should be the only type out there and all variations should be banned, lol.
With that in mind, I was very interested to see the introduction of an upgrade from iHelpUTech for the Icom IC-705 which swapped out the Micro-USB and replaced it with the far handier USB-C. Now let's make it clear from the get-go that this 'upgrade' does not upgrade the USB connector's functionality and does not allow for any USB-C charging benefits - it merely gives you the convenience of having a USB-C socket.
So is it worth changing the control board just for that?? Well that's a personal choice, but with this new control board you also get a vast improvement in protection for the radio when using an external amplifier. That alone is worth swapping out the board!
The tiny transistors inside the original Icom control board can only handle a very small amount of current and in some cases they could easily be destroyed with just a few mA whereas the new control board has transistors which can handle around 1A, so that's a HUGE safety margin, should there be any spikes.
The board cost £68 and I think that's a reasonable price to pay for this convenience and protection. The actual fitting of the board is an absolute doddle and all you need is a screwdriver to complete the job.
First of all, remove the battery, followed by the four screws on the back of the radio. Then you remove the top and bottom screws holding the front panel on and gently pull apart, noting that there are a couple of ribbon cables connecting the two halves together.
I left the ribbon cables in situ and simply rested the two halves next to each other. You can see that the control-board is held in place with 3 screws, so remove those and gently lift up the control board and remove the ribbon cable once you've lifted the tiny black release-tab.
Then connect the ribbon cable to the new control board, close the release-tab and screw the board back in place, but before tightening, insert a USB-C cable into the port to make sure it's aligned properly.
Join the two halves of the radio back together and before inserting the screws, refit the battery and make sure everything springs back to life. Insert a USB-C cable and plug it into a charger to check that the 705's charging light comes on. If it does, you can screw the radio back together. Job done!!
Below is a video from iHelpUTech covering the whole installation....
VIDEO
This installation was super easy but the previous owner of my radio (for whatever crazy reason) decided to Loctite the upper and lower screws in the front panel which resulted in me totally stripping one of the screws 😡😡😡 If the screws don't come out easily, make sure that you have the absolute correct screwdriver or the same will happen to you. These radios require a JIS type screwdriver.
Last Easter I built a 5-band QMX and although I found it quite a challenge, it worked from the get-go and I was really pleased with myself! I get a lot of pleasure from building electronic kits and this will be the sixth one from QRP-Labs.
My only gripe about the QMX build was that the design left the components incredibly tightly crammed in, and I wondered why they hadn't made the PCB just 10mm wider. But since then, I have read Hans Summers' document explaining that, for him, it was a design-challenge to come up with such a compact design. Well, he did an amazing job!!
Anyway, here we are a year later and I see that Hans has released the QMX+ transceiver kit. This time, the design has much more space between components and I'm anticipating that the build will be far easier than the original design.
So what is a QMX+?? Well it's a high quality 12-band MultiMode (CW/DIGI) Transceiver which can be purchased as a self-build kit or as a pre-assembled unit - it's worth noting however that there is a very long waiting list for pre-assembled units - maybe up to 6 months 😮
In terms of functionality, the "PLUS" version is little different to the standard QMX but it has the advantages of being able to house a GPS unit, an SWR Bridge, a Real Time Clock (battery backed), a Developer's Kit and maybe even an ATU in the future. Hans also has other "secret" plans for the ongoing development of the QMX+ including SSB Mode which will be awesome!
I feel (and I may be completely wrong) that the QMX+ is a big step toward the release of the fabled QSX which will be an All Mode transceiver with who knows what features.
I currently own a couple of (tr)uSDX transceivers and these are simply amazing little radios which are multi-band, all-mode SDRs with built-in sound card, speaker, mic, keyer, PTT, etc. But their performance is far from perfect. Don't get me wrong - I love them - and when you're up on a hillside playing POTA or SOTA, their performance will bag you many contacts for little outlay. But they're just not in the same league as a QRP-Labs product.
I'll always remember when I built my first QRP-Labs kit - the QDX. It went together well and it performed superbly!! I was getting better results on my 5W QDX than my Multi-Watt IC-7300. I was (and continue to be) very impressed!
Sorry - I'm rambling. Let's look at the QMX+ Kit. It arrived in a single box which contained all the relevant components, each type being bagged separately. I'd also ordered the optional GPS Module plus (of course) the metal enclosure.
The quality of this kit is extremely high and I've yet to come across a QRP-Labs kit with missing pieces. The aluminium case is strong and well finished, with sharp text on the end plates.
The Assembly Manual for the QMX+ is extremely good (as usual) and I intend to follow the instructions to the letter, just as I've done before.
In addition to having access to the manual electronically, I also decided to print a copy so that I could read through it prior to starting the build and highlight bits which I think warrant special attention, making notes in the margins of the page. I also use the printed manual to mark off each completed section.
I had decided to do this build at the weekend while I was at our caravan - nice and peaceful with no distractions. Prior to going there though, I wound all the toroids and then bagged them individually in tiny sealer-bags with ID labels.
All pretty straightforward but the most tedious was L506
Before starting the build, I laid out all the components and marked off the capacitor values. Once that was done, I fitted the caps, the diodes and the inductors. Very simple.
After that I installed the BS-170 transistors, clamping them in place before soldering.
Next up was to install all the toroids and the trifilar. Since I'd pre-wound these, it was a breeze to fit them all and once I've adjusted them as part of the 'tuning' procedure at the end, I'll probably drop a few blobs of hot-glue on them to keep them secure when the radio's in transit.
At this point of the build I realised that I was rocketing ahead and was being a little blasé, so I purposely slowed down and checked everything I'd done so far.
I have to say that for whatever reason, I seemed to be struggling with my soldering on parts of the board. At first, I thought it might be my soldering station, so I switched to another soldering iron and things improved - this board demands a soldering iron capable of holding its own! Of particular note, some of the solder-pads are TINY and it can be real difficult to get the tip of your soldering iron onto both the pad and the component at the same time. If you look at the adjacent image, you will see that some solder-pads are way, way smaller than others and some of the pads are barely visible.
When it comes to winding the T501 Transformer, you have to decide whether you want a 9V radio or a 12V. I opted for 12 and for this you are strongly advised to choose the "RWTST" method of winding (Really Weird Twisted Sister Transformer) and boy, it certainly is weird!
I'll be honest and admit that the first time I wound T501, I wasn't confident I got it right, so I unravelled it and started again. I was struggling to understand the diagram (see below).
Diagram From The Manual
In the hope that it will help others, I have redrawn this and although it makes sense to me, it may not to you 😂....
After that, I put the two power boards together and fitted them to the main pcb. You have to be very careful to read the instructions and slow down when you're fitting these. Read a couple of pages ahead before beginning!! I totally forgot that the black connectors have to be mounted so that there’s a gap below them. I just about managed to get away with it (der!).
I then started fitting all the 'hardware' such as the BNC connector, power connector and 3.5mm sockets before installing the LCD panel and battery board.
With everything installed (don't forget the link under the GPS Board (if you bought one)), it was time to slide the PCB into the lower half of the enclosure.
Before you do though, spend some time examining the pcb to see if any of the component legs need trimming down, because there's very little space between the underside of the pcb and the metal enclosure and it's very easy to end up with a short.
I purchased some amazing little side-cutters from the local £shop which were perfect for the job! To be honest, I thought they might be junk, but they turned out to be the toughest fine cutters I've ever bought, so I went back and got another pair 😊
With everything put together it was time to apply power and see if any smoke emanated from the case 😬. In case I'd made a mistake (or two), I opted to use a current-limitedpsu to avoid damage on power-up.
FIRST TEST >>>
When I switched it on, there were no lights, no display, no noise, nothing! And thankfully there was no smoke!
Before anything will work, you have to connect the radio to a computer with a USB lead and install the firmware, but when I did this, the USB was not recognised. I tried a different lead and even a different computer - nothing! 😰
I checked and double-checked the pcb for any obvious signs of faults such as dry joints, solder shorts, etc, but there was nothing obvious. I could see 9V at the power switch.
I sought help on the Groups.IO forum and got nowhere initially, so I submitted a trouble-ticket at QRP-Labs but six days later there was no response from that either.
It's extremely disappointing when stuff like this happens and I know there's bigger problems in the world, but neverthless I'm feeling quite disappointed considering that I've successfully built 5 other kits from Hans (including the regular QMX) and a few from other kit manufacturers.
A few days on and members of Groups.IO started to make suggestions and I learned that there should be voltage at Vcc and Vdd but there was none on mine. The thread got busier and someone suggested that I try swapping out the Power Boards from my QMX to my QMX+. Before I risked that, I decided to order a variable voltage/current psu to further reduce the risk of damaging the boards. With it, I could reduce voltage to maybe 7.5V and 200mA.
Before swapping out the boards, I recalled my soldering struggles and decided to reflow virtually all the connections to make sure that I'd not got a bad joint somewhere which was causing these issues. The Ground Plane on this pcb really does suck the life out of your soldering iron!
I decided to remove the power boards and the GPS module. It was then that I discovered I actually had a short on Vdd. No amount of probing with my DMM helped discover the source of the short, so I’ve given up for now.
I’ve approached an electronics professional friend to see if he can afford the time to do some fault-finding for me. If not, I might have to order another and start all over again 😪.
Part-2 to follow!
UPDATE >>>
Regrettably, my friend is in the process of moving to another country(!) so I'm now proper stuffed 😂 I guess I'm going to have to write this off completely.
I was thinking of ordering another one and trying again, but this build has made me a little weary. Plus it's highlighted the fact that without any electronics knowledge, I've just been a lucky constructor up to now.
I'll have to sleep on it 😓
UPDATE >>>
On a more positive note, G4GIR very kindly offered to look at the board for me, so I've popped it in the post to him and await his verdict. Let's hope it's nothing I've done 😂😂😂
Having owned some of the best transceivers in the world, is it a surprise to see what it's been whittled down to today? I guess many will think I'm an out and out nutcase, but the fact is, I've experimented and enjoyed every minute of it. Being the sort of person who loves a bargain (and the art of negotiating), I've managed to snaffle some fantastic deals over the last few years which has usually allowed me to get my money back when I've sold the equipment and even make some money along the way. Sometimes I've been able to pass on a bargain to a friend, which is also nice. I learned that you can get a 7610 for under £2400 and you sell one for the same amount 4 years later. You can buy a KX3 for £700 and sell it later for £1700 😮
Farewell my beautiful friend
The very best radio I've owned was the IC-7610 without a doubt. Better than my FT-DX101D and better than my EE MB1 PRIME. It was just a magnificent machine, but I had to face the fact that I barely used it since buying a holiday home. The big radios just sat gathering dust in my shack and with times being how they are, it seemed ridiculous to have all that money sat idle, so I thought long and hard about how I typically spend my radio time and made some drastic changes.
Being unable to have a 'proper' antenna at my home QTH was always the elephant in the room. I had two EFHW's oriented North-South and East-West and that's it - they were the best I could make of a bad situation. Having said that, I've managed to bag some seriously good contacts with those antennas and the 7610.
But I've also bagged some amazing contacts from the shack using a £60 QDX and a £90 (tr)uSDX. So you have to question the cost-efficiency of those big radios, especially when you are a QRP operator.
So, with the jewel removed from the crown, I decided that my IC-7100 would remain in the shack and become my main radio there. It's the only transceiver in the world which covers HF, 6M, 4M, 2M, 70cm and DSTAR. These are probably the most underrated radios of all time and it will be fine for everyday use.
Because the 7100 isn't an SDR radio with all the benefits of a scope and waterfall, I also installed a HERMES LITE 2 PLUS which is simply incredible value for money and has some of the best software available at any cost! I recently spotted another one of these on Facebook Marketplace for £200 and the day it arrived, I posted out to a buyer for £275 😁
For things like POTA and FIELD DAYS where you have the benefit of being in a vehicle, I have the stunning MISSION RGO ONE radio which is just an absolute joy to use. For SOTA type outings I use the tiny FX-4CR transceiver which has become one of my all-time favourites.
And that leaves the glorious IC-705 for no other reason than I love it. I very nearly sold this and then came to my senses. It's the most advanced QRP transceiver in the world - bar none! Apart from covering HF, VHF and UHF, it also has a myriad features and functions that leave you in awe of the Icom design team.
Have you changed your shack a lot? Or are you the sort of person who sticks with the same trusted rig for years? I'd be interested to know in the comments section below.
Three and a half years ownership of the ICOM IC-705 have passed and I thought it might be an idea to take another look at it to see if it still rules the roost for Portable Radios in 2024. In this 'look back', I'm only going to focus on what I've been doing and how well the 705 has worked for me. My original review is >>HERE<<
What should I compare it to? Well I guess a KX3 would be a likely candidate but boy, they are not only difficult to obtain right now, but they're also incredibly expensive unless you buy an old, early production one.
But has the Elecraft got the better receiver? Yes - there's little to beat the KX range in terms of outright performance, that's a given! If you want to hunt down the very faintest, weakest signal, then you stand a better chance of success with a KX.
But for the other 99% of the time, when you've driven, walked, hiked to the perfect take-off spot and set up your antennas, there's little practical difference between a KX3 and the 705. Or between a 705 and an 817. In fact, my $89 (tr)uSDX will probably get you as many QSO's in the log as the others from the top of a hill!
Over the last couple of years I've relied almost exclusively on my IC-705, using it outdoors, on hillsides, in the back garden, in a park, at the caravan, by the seaside and even at home as a base station. It's been utterly reliable and surprisingly tough even though it's not been wrapped in cotton wool. Unlike my Elecraft, I've never really worried about it - I guess I look upon it as a bit of a workhorse. If it gets a little scratch or a ding, it doesn't really matter. I don't believe it would substantially affect its resale price either.
The notable difference between the IC-705 and other radios is flexibility, features and what I call 'friendliness'....
The Icom IC-705 is more feature-rich than any other portable radio. It puts together such an awfully good package that you don't have to buy anything else (assuming that you use resonant antennas). You can operate throughout HF, 6M, 2M and 70cm on LSB, USB, CW, AM, FM, DV and DSTAR.
With the radios built-in server, you can operate remotely. With the built-in WiFi you can tether to your mobile phone and operate Digital Modes out in the field. Thanks to the built-in GPS, you can even ensure accurate timing for FT8, etc.
Forgot to take a pen for logging your QSO's?? Don't worry - you can record all QSO's onto the SDCARD and run back through it later to get the callsigns - it even records the time and date of each individual QSO!! How good's that??
After using it so frequently and for so long, I'm now in that happy place where I know I just need to grab my small rucksack and head off outdoors for some radio fun. I don't need to carry a million bits of ancillary items - it's just my radio, my antennas and my iPad. If I'm just going out for a couple of hours, then I rely on the Icom battery, but if I'm out for the day I will take a 13.2V LifePO too.
Up on a hillside, I tend to stick with 5W and there's little need for more. Usually, the take-off is excellent and my SotaBeams Dipole works amazingly well - enough to have SSB chinwags across to America from the UK. In fact, one of my favourite chats was from a beach to two hams in America using only 2.5W (KE5EE and WD4NGB).
If I'm struggling to get a response to my CQ calls on 5W, I might move up to 10W, but once I establish contact with someone, I ask them to let me drop to 5W and get another report. If the report is very good (it often is) then I'll ask for another at even lower power. Needless to say, I don't want to make the QSO hard work for the other operators, but most people are happy to experiment with me and they often end up dropping their power to me too and because they've been so used to knocking out 400W+ for years, they've forgotten how far they can get on a tiny fraction of the power. All very entertaining (to me at least) 😂
I have to admit that it's easier to answer someone elses CQ Call than it is to get a response to your own CQ Call at QRP levels. But patience often does reward. I find that using the IC-705's TX Memories makes light work of repetitive calling. I have a Long and a Short CQ Call recorded in memory and it's easy to set a TX-Loop going. The call is repeated over and over with a small pause inbetween to allow you to listen for any responses.
Once I've finished with SSB, I tend to briefly switch to the 705's CW TX-Memories and put out a "CQ TEST" for a few minutes on various bands to see how far I get on the Reverse Beacon Net before switching over to DSTAR depending on how close I am to a repeater. The IC-705 comes with a comprehensive list of repeaters already programmed in and thanks to the built-in GPS it can quickly determine which repeaters are the closest to your location and list them in order of distance (showing you the distance of each one in miles or kilometres).
After DSTAR I might switch to FT8 which gives me a chance to grab a drink and a sandwich.
The IC-705 has proven to be a true all-rounder and can seemingly do it all, without any fuss or alterations or expensive plugin modules. The only thing that isn't included is an ATU, but neither does the KX3 come with one (unless you pay almost £300). Most of my portable antennas are resonant, so I usually have no need for a tuner, but if I want to use a multi-band end-fed, then one is required.
I own two ATUs - the LDG Z100PLUS and the Elecraft T1. My favourite is the Elecraft T1. It's compact, light and incredibly good at finding a match - quickly!! And finding a quick match is very important when it comes to QRP equipment because many QRP Transceivers don't seem to have a very robust PA, resulting in blown transistors during long tuning sessions.
Thankfully, the 705 is pretty strong in this respect and I've never had a problem when tuning up using any of my tuners.
The success of the IC-705 in the marketplace has led to much third-party and community support. One of the most useful addons for the 705 is Marcus Roskosh's SDR-CONTROL app which not only provides remote-control operation, but also provides a host of other tools which make the 705 (or 7610 or 9700) an absolute dream to work with. It's a game-changer.
SDR-CONTROL is available on IOS or MAC and I personally use it with my iPad 11. It performs flawlessly with virtually no lag between the readings on the radio and the readings on the iPad. It's all very fluid!
All the functions of the radio are available on the software display and the bandscope and waterfall are superb!! It's nice and easy to adjust the bandscope to increase the signal-peak display size and the ratio of scope to waterfall. The meter is nice and clear but I was hoping for an analogue option which isn't there (in the current version). Long-pressing the "TUNE" button sets the power to 10% (adjustable in menus) and transmits in AM mode so that any attached tuner will activate safely. Long-pressing the PTT button will allow you to choose between the radio's mic or the iPad's mic.
VFO AandB are visible onscreen and it's easy to switch between the two. Everything is very intuitive and there's never a struggle to figure anything out. Take FT8 for example - you can switch to it and be making contacts within seconds! No fiddling around with cables, no special drivers or VACs - it just works. Simple!
Any FT8 contacts that you make are logged automatically and that brings me to the next feature in the SDR-CONTROL toolbox - the LOGBOOK. Yes, there's a logbook built-in and it has an easy export function to transfer your contacts to your QRZ, etc.
By clicking on a button, you can see the full contents of the ToolKit which includes some very handy features such as the DX Cluster. This can show you active signals on the bandscope, allowing you to quickly spot and engage desired DX. There's also a BandPlan, a set of CW Macros, QRZ LookUp and PSK Reporter.
There's lots more to this amazing App and it adds so much to the already pleasurable IC-705. I suggest that you go read the manual by clicking on the image below to find out much more about it...
So, as you can guess, I've been very happy with my 705 - probably more so than any other radio I've owned (and that's saying something). It does pretty much everything I want and it does it all simply, effectively and without fuss. I can play on all the ham bands, in all the modes, I can do analogue and digital and I can enjoy fantastic support from third-parties and a knowledgeable community.
What do I dislike?? Not much really - in fact it seems a bit churlish to complain when a radio offers so very much. If I had to be Oliver Twist and ask for more, then.... I'd ask for CW Decoder instead of the RTTY Decoder. Having said that, the 705 interfaces very easily with my PreppComm Morse Encoder/Decoder....
I do believe that the IC-705 is genuinely the best portable transceiver ever to hit the market. It offers such great value for money and has so many features and functions. And it's not just about the specification list - it's about how everything works - it's incredibly intuitive. Everything falls to hand and makes sense.
There's so many features which make life easy for the operator and where some radios end up looking like a bowl of spaghetti when trying to do something different, the IC-705 often does it wirelessly via WiFi or BlueTooth. Even small things like getting a pair of AirPods working - I've come across so many radios which have BlueTooth but then fail to connect to BlueTooth headsets! The Icom even works with Yaesu's headsets! The very fact that you get a server built into the radio to enable remote operation is pretty darned amazing - especially when you consider that even Yaesu's £3,100 Flagship 101 doesn't have such a feature 😮.
And yes, the £45 SDR-CONTROL software significantly adds to the richness of the 705 which some might say is down to Marcus Roskosch and not the radio, but the fact that the Icom is flexible enough to permit such interaction/connectivity is something that should be applauded.
Okay, so what about something other than a KX3 or 705? Let's say you bought an FT818 or a G90 or a TX-500?
Well for a start, I wouldn't even give the Russian-built TX500 a second thought because I wouldn't want to support the economy of the disgusting terrorist Putin. Although the HF TX-500 is a very visually appealing transceiver and is around 2/3rds of the price of a 705, it lacks most of the features that I personally value.
The G90is a fabulous budget HF transceiver which offers lots for little, but at the end of the day, it's a cheap Chinese radio which I could never consider to be my 'forever radio'. Like the TX-500, the G90lacks valuable features.
The FT818 is an old favourite of most hams. It's been out there for over 20 years and at half the cost of a 705 is always going to be the QRP radio of choice for people who are happy with the basics. But let's face it, it's old technology and looks like a dinosaur compared to the 705. A rugged, reliable shack-in-a-box but limited in a modern world.
So in summary, I am still over the moon with the Icom IC-705 and I'm glad I invested in it. In the past, radios have 'come and gone' but this one has stayed with me and I can't imagine a time when I would swap it for something else. Maybe Yaesu will bring out something to compete, but I can't imagine how they'd actually make something better! If they do, I'll be all over it 😁
HIGHLY RECOMMENDED!
Please remember that these are just the opinions of an M7 operator. My goals, desires and requirements will be different to yours. I'd be interested to hear about them. Please feel free to leave a comment below and include your CallSign if possible. 73, Tom.
UPDATE <<<<<<<
Read THIS POST to see how I connected the 705 with an Expert Electronics ColibriNANO SDR receiver to provide a large screen panadapter.
UPDATE <<<<<<<
Read THIS POST to see how easy it is to use an external amplifier with the IC-705, in this case an MX-P50...
UPDATE <<<<<<<
I paid over £20 for my tilt-stand and although it's good for shack use, it makes it a little awkward to fit neatly in my ruckshack, so I've started using a couple of 25mm roundhead bolts instead. Takes seconds to lightly screw them into the base and it results in the radio being tilted to the perfect angle. I got the screws from the local £shop in one of those little multi-pack screw sets.
SMA Caps hot-glued to bolts to provide non-slip solution
Most hams who love to operate outdoors, prefer to work at QRP levels. Being in the great outdoors usually gives you a fabulous take-off and provides a super-low noise-floor. 10W, 5W, even a couple of Watts can get you across the Atlantic on SSB and that’s something that just thrills me and keeps me interested in the hobby.
Back home however, all the stars need to be aligned for long distance QSO’s to take place. It’s doable of course, but it can be hard work for people at the other end of your transmission, which means that I avoid joining in on any overseas Nets. It’s the main reason that I don’t do much transmitting from the shack. No big deal, cos during Spring, Summer and Autumn it’s easy to setup outdoors. A pleasure, in fact!
I actually have a Xiegu XPA125B amp (boxed and on sale (now sold)), which produces 100W from a 5W input, but it’s useless to me (it came with a radio that I bought (X6100)). The problem with it is that you can’t turn down the power - it’s 100W or nothing! I’d keep it if I could feed it with 1W and get 25W out. Why?? Because at the end of February OFCOM will be allowing Foundation License holders to use 25W.
What I wanted was an amp which would provide me with 25W comfortably without putting strain on it. I looked at the Neptune 50W but, for the amount of use it would get, it was more than I wanted to pay (and I couldn’t find any used models anywhere).
And then I read some reviews of the MX-P50 made by Sun Xiao in Shandong, China. Being a very happy owner of a fabulous radio from China (FX-4CR), I'm not one of those "Let's hate China" brigade, so the MX-P50 seemed to fit the bill. It was just a case of finding a used one for a decent price.
With the 80-10M MX-P50 being able to produce 45W from a 5W input, I knew that it would be positively coasting along at the 25W limit I’d be setting, so longevity shouldn’t be an issue.
When it arrived, I could see that it had never really been used. It had been a backup amp to a HardRock/Hermes setup and had spent most of its short life in the box. The amp is really very compact and light - great for those who want to take it with them on a Field Day.
Apparently, it works well with a range of radios including the FT-817, KX3, IC-705, etc, but people using more obscure transceivers may experience issues.
The amp’s power cable was fitted with Anderson Power Poles and the interface cable was terminated with a 3.5mm stereo jack plug. This was perfect for my Icom IC-705 and worked straight from the get-go.
I know I'm drifting a bit here, but I think it's important to realise that amps can send current back into your radio if a spike is generated by the relays during switching. This current might be small, but it can cause damage to your radio's keying circuitry. This isn't a problem unique to the MX-P50M - it can happen with any generic amp.
I'm guessing that most people ignore this potential problem (or just aren't aware of it) and probably get away with it, but I don't want to put my radios at risk, so I use a buffer device from a guy called RADIODAN in the USA. He calls it an RBI-1 (Relay Buffer Interface) and it can be adapted to work with virtually any radio (although he sells specific interface kits anyway). It will work with any radio that has a keying output which goes to GROUND when transmitting.
Using this relay buffer provides peace of mind and is (IMHO) a very worthwhile accessory for all your QRP radios - all you need to do is make up a different lead for each keying connection type - for example on many radios it will be a simple 3.5mm jack, while on others it will be phono (RCA) or even something like a multi-pin DIN.
There is also a 'mod' which can be carried out to prevent spikes into your radio involving you opening up the amp, cutting a couple of wires and soldering few small components. It's detailed HERE in this video where the construction method is better explained. The mod was designed by Kevin Loughin and his video can be found HERE. When I opened up my amp, I discovered that the previous owner had already carried out the mod.
So, back to the amp itself. When connected to power the MX-P50M circuit is live all the way through to the relays even though the Power Toggle is in the OFF position, so don't switch the amp off thinking that it's not draining any power from your battery - it is - only a tiny amount, but it's there.
With all the connections made between the MX-P50M, the RBI-1 and the IC-705, I switched the amp on, set the radio's power to 1W, switched to CW and briefly stabbed the key - the amp worked! I sent a few more dits and dahs before switching over to RTTY mode and keying the mic to send a more sustained output. Everything went well.
Now it was time to insert a Power Meter so that I could find out how much power into the amp would result in 25W out (to the dummy load). With the meter inline, I observed the following results...
The power-out reading on the radio pretty much mirrored the power-out on the meter (x10), so that was great. It altered slightly on different bands, but not a mile off. So 2.5W in, 25W out 👍
Obviously, for those who are licensed to use it, there's 45W available. So there you have it, a nice little amp which is just perfect for UK Foundation License holders and their QRP radios.
73, Tom, M7MCQ.
MX-P50M HF POWER AMPLIFIER
Specifications
Frequency Band : 80m 40m 30m-17m 15m-10m Operating Modes : SSB CW AM, RTTY and FM-Reduced duty cycle RF input : 5W Output power : 45W+ Band mode : Manual Power requirement : 13.8V 8A , RED “+” BLACK “-” Cooling method:passive air cooling Antenna connector : SO-239 50Ω Size : 155*100*35 ( mm )D*W*H Weight : 0.55Kg
