AERIAL-51 MODEL 404-UL

There’s no such thing as a perfect lightweight multiband antenna for outdoor use. I’ve tried lots of them over the last few years and the one which has brought me the most success is the SOTABEAMS 20/40 Bandhopper II Linked Dipole. But that covers just two bands.

I have another Sotabeams antenna called the BandSpringer Mini - an End-Fed which covers 7 bands, but for some reason it’s not been a raging success for me, so I seem to be on this never ending search for the holy grail.

Anyway, I decided to try something different - something which I’ve never tried before - an Off Centre Fed Dipole in the form of the MODEL 404UL from Aerial-51.

This Kevlar-strengthened antenna can handle up to 200W and yet it’s extremely light and compact, weighing just 400g including 40ft of coax! Having something which can handle so much power gives you a satisfying reassurance that your FT8 transmissions are not going to overheat the Balun even at 25W. 

The antenna is just as simple to erect as the Bandhopper and although they recommend using something taller, I used my 7M Mast to great effect. You can see in the photo below how it looks. The 40ft coax allows you a great degree of flexibility in choosing where to operate from (a heated garage in this test-case, lol).

TYPICAL SWR READINGS

 

You can see that the profile of my Inverted-V is quite shallow compared to the 404UL diagram, but nevertheless, it really pulled in the signals. 

 

QUICK SAMPLE OF THE 404/705

 

I’m keeping the antenna in this “test location” for another week and will update this page after that. I bought the 404 as a secondhand item and so luckily got it at a bargain price. The value for money was further enhanced by the WindCamp case it came in, plus a pair of mini-reels for winding in the elements (with their string supports) for quick storage and deployment.

After a while, I dumped the reels in favour of normal winders from SotaBeams.

73, Tom, M7MCQ.

Micro PA100 100W HF Amp

I recently I came across an amp at a radio rally and it was for sale at just £50 “SOLD FOR PARTS”.  I got my phone out and Googled the device to learn more about it and discovered that they cost £200 new, so I decided to take a chance on it, figuring I could make a quick buck by selling it on Ebay after reviewing it. Sadly, when I got it home, it didn’t work. Dead as a Dodo!  I was gutted, but figured I’d open it up to see if it was a melted mess inside. 

The PCB and all its components looked to be absolutely as new and in perfect condition - just couldn’t figure it out. After spending time staring at the PCB, I noticed that there was an unusual fuse holder. I removed the fuse, tested it and found that it was blown. Needless to say, I didn't have any of these tiny fuses in my box of bits, so I ordered some on eBay and waited for them to arrive (from China).

When I replaced the tiny fuse, I powered the amp up again, using a current-limiting power supply, half expecting it to blow again. But it didn’t! 

With everything apparently working as it should, I connected it to my IC-705 and a Dummy Load. Dropping the 705’s power to 500mW, I got 20W output from the PA100 into a dummy load. A big smile appeared on my face 😄. I started to increase the power and with a full 5W in, it showed 110W out.

The next step was to connect it to its “natural partner”, the Hermes Lite 2. As mentioned in a previous post, I wanted to take advantage of the ability to run the amplifier output through the Hermes’ Pure Signal processor by adding an RF Sampler. 

With the Hermes putting out 750mW the amp was outputting around 25W - perfect (for me).

I went on the 40M band and broke into a QSO between two English operators with booming signals. I was eager to get a good report from them. Sadly, this didn’t quite go to plan 🙄. When I keyed up, I could see distortion on the panadapter and one of the operators told me my audio was indeed badly distorted.

Without any idea what was causing the distortion, I removed the RF Sampler and tried again. This time, the outgoing signal looked perfect and so I recontacted the operator I’d spoken with moments ago. He confirmed that everything sounded fantastic. He told me that there were some Linearity settings in Thetis which would probably resolve the issue.

Sitting there, I wondered if it was simply a case of there not being enough attenuation in the sampler’s coupling output (-50dB), therefore overloading the HL2’s Pure Signal input 🤔. I’d need to add some inline attenuators and experiment more. But that’s for another day - I don’t want to detract from the performance of the amplifier.

The Micro PA100 is a very compact device, with a 100W (or more) output on the 80-6M bands. It has automatic band sensing or you can provide your own interface lead to let your radio force band changes. There is information in the manual to help you achieve this.

I didn’t have an interface lead and since I’m going to be selling this amp, I can’t see the point in making one, so I used the band-sensing and it worked amazingly well - faultlessly even!

The amp also has RF-Sensing which means that you don’t need to fit a PTT SEND line - just transmit and the amp instantly detects the RF. It works well, but I’d still recommend fitting a lead between the two devices. The menu has options for Icom, Yaesu and Xiegu protocols.

Unlike say a Xiegu XPA125, the PA100 doesn’t have an ATU so I connected an LDG Z-100Plus. Now this would present a problem in that initiating a tune could mean the amp could potentially see huge amounts of reflected power and very high swr during the tune-cycle (it will protect itself if it sees anything greater than 2:1).  Thankfully, the PA100 has a BYPASS mode which is accessed by a simple press of the Function button. Once the ATU has found a match, it’s just a case of pressing the Function button again. 

There’s an impressive amount of protection built into the amp which keeps an eye on high swr, and high temperature - there are two fans fitted in a push-pull arrangement. The fans are quick to switch on and although they aren’t noisy, you are certainly aware of their presence. 

There’s also that tiny 20A fuse which protects from over current and even from applying the power supply the wrong way around (I am so pleased that the previous owner wasn’t aware of the existence of the fuse) 😂🤣😂.

The front panel sports just two things a screen and a button! The display is pretty small but extremely clear and easy to read, providing all the information you need. The (function) button switches between PA ON and PA OFF (bypass) and also gives access to other functions. It’s a little odd, but you soon get used to it. The only thing that concerns me about it is that it sometimes doesn’t detect a press which can be annoying. It also makes me question the longevity of the button.

Other than that button though, I must admit that the construction of this cheap Chinese amp is absolutely excellent!! The pcb seems to be a high quality item and the components look to be very well soldered and carefully placed. There’s not even a hint of “cheap tat” that you often get with these budget devices. Everything looks top notch. It’s also a ‘clean’ amp with a measured -60dBc separation between the wanted signal and any unwanted harmonics.

Note the huge heatsink

CONCLUSION

Putting aside the fact that I got this amplifier for a ridiculously low price, I have to say that the Micro PA100 is a great little amp, brimming with features, versatility and safety. It’s good to know too, that the designer is constantly updating the firmware in order to improve the product.

If I needed a 100W amp, then I wouldn’t hesitate to invest in one of these. They can be used with virtually any transceiver, without the need for an interface lead and you’d have to be an idiot to do it any harm (sorry previous owner).

Its compact dimensions and light weight mean it can easily be taken on POTA outings. It’s just a great little all-rounder. For a Foundation License holder, I like the fact that you can transmit under a Watt and get a solid 25 Watts, giving both radio and amp an easy life.

Before I sell it, I’m going to resolve the RF Sampler issue, just because I want to understand what the cause is.

UPDATE : March 11

I ordered some inline attenuators from AliExpress and in view of the severe distortion that I experienced when first trying out the RF Sampler, I connected 30dB attentuation and BINGO it worked a treat!

The amplified signal from the Micro PA100 was now being processed by the HL2’s Pure Signal circuitry and corrected, resulting in a beautifully clean signal. I had many QSO’s all over the world and received complimentary audio reports.

Again, a HUGE round of applause 👏 to the Hermes Lite 2+ for its outstanding value for money. And more applause 👏 to MI0BOT’s version of Thetis and more again 👏 for the wonderfully cheap Micro PA100!

Amp for sale (with sampler) £200!

Thanks for visiting the blog!

73, Tom, M7MCQ.

Manual

PURE SIGNAL - HERMES LITE 2

HOW DO I  BECOME PURE?

People email me saying they've read my blog-posts about the wonderful Hermes Lite 2 but point out that I don't provide instructions on how to use Pure Signal, so let's fix that right now!  It's a very simple process and can be achieved quickly. Using PS is detailed in the manual, but it seems some people don’t read them, lol. Bear in mind though, I'm a simple M7 license holder, so everything written below is based purely on experimentations. 

There's actually a couple of ways of doing it - internally or externally. I have only used the HL2's internal method, but that might change as I go along.  Anyway, let's start with the easiest way first of all. Anyone can use this method and there's no extra parts to pay for it you already have a Pure Signal output.

Pure Signal (an advanced, adaptive predistortion technique) is used to significantly clean up your transmitted signals by reducing distortion, IMD (Intermodulation Distortion), and harmonics. By sampling a portion of the output and correcting for nonlinearities, it improves transmission quality, reduces splatter and enhances efficiency.

In order for Pure Signal to function on your Hermes Lite, you must start by switching on PS-A (which is the Pure Signal Auto calibration) and DUPLEX (meaning that the radio receives even when transmitting). This is so that the transmitted signal can be monitored, measured and subsequently adjusted. So go to your Thetis software and switch it on (by the way, I'm using V2.10.3.12)...

Then you need to switch on AGC AUTO by double-clicking the text above the AGC until it switches from S-ATT  to  A-ATT. If you forget to do this, Pure Signal will not work properly.

Then go to the menus at the top of the screen and click on LINEARITY. A screen will appear - make sure you have all these settings...

Now find a clear spot on your preferred band and transmit. You will notice that the green   Feedback/Pure Signal 2  markers will change to indicate that your transmission is being examined, measured and adjusted...

That's it! You have PURE SIGNAL! 

 

WHAT ABOUT CONNECTING AN AMP?

So when you use the internal method, everything leaving your HL2 antenna port will be pure as the driven snow. But what if your pure signal goes out to an amplifier? That amplifier could undo all your good work!

Up to now, I've not seen a single post on the internet about this. There's little bits here and a few hints there, but no simple, straightforward guide on how to use Pure Signal with a HL2 and an Amp. So let's hope this post fixes that situation.

In this case, you want to monitor the signal leaving the amp instead of the radio. To do that you need a special splitter which is actually an RF SAMPLER. There are a few samplers available on the market and in the example below, I've shown an Australian sampler from VK3AMP in the illustration...

You will note from my diagram that the Pure Signal connector on the radio is actually an INPUT and not an output as some mistakenly believe. It's very important that the RF Sampler output to this connector is -50dB or greater to avoid overload. Ideally, you should connect the sampler directly to the amplifier's output connector. In the above case, it would mean using an PL239-PL239 Male pass-thru. 

😂 A pretty diagram versus reality 😂

If you are going to insert an ATU in the circuit, it's going to be between the RF Sampler and the Antenna. You should (in this example) put the amplifier into BYPASS mode during tuning.

Note that I have included an RF Choke in the mix too - that's only because I often use a ground mounted vertical which generates problematic common mode currents. If you have no need for one (or for an ATU) then ignore. In this case, the layout would be simpler still...

So there you have it! Pretty straightforward huh? But what if you don't yet have a Pure Signal connector on the rear panel of your transceiver? Don't worry, it's a very simple and cheap mod - all you have to do is buy an RG-178 pigtail from Amazon (other stores are available lol) and solder one end to the connector block which connects the HL2 PCB and the Filter Board.

Note that the center-conductor goes to pin-6 and the shield (twist it all together) goes to both pins 3 and 4.

HL2 Internals

Close-Up

I hope this post proved to be useful to you.

73, Tom, M7MCQ.

 

UPDATE : 24 FEB 2026

Found a competitively priced RF SAMPLER here in the UK - just ordered one for £44. It gets good reviews, so happy days. Also ordered a couple of inline SMA-SMA attenuators in case I need more attenuation than the sampler provides.

The sampler arrived very promptly from the supplier, well packaged and the whole thing looked to be constructed to a very high standard. Excellent value for money!!

If you wish to purchase the VK3AMP sampler, click here. ($150) 😵

 

If you are from the STATES, perhaps this sampler would be a better option....

And here’s another option…

https://www.60dbm.com/product/55db-100w-1-55mhz-rf-sampler-for-pure-signal

73, Tom, M7MCQ.

Q: Explain Pure Signal on the Hermes Lite 2 HL2 + Plus

Q: How do I use Pure Signal on my Hermes Lite 2?

Q: How do I use Pure Signal on my Hermes Lite 2 with an AMPlifier?

Q: How do I connect my amplifier to Pure Signal on the Hermes Lite 2 HL2 Plus?

TECHMINDS SHOCK 😮

Well, I never saw that one coming! Turns out that M0DQW is a child rapi$t 😮😮😮 Matthew Miller ran the very popular ham radio YouTube channel, TECH MINDS, with over 150,000 followers. 

Thankfully, he is now in jail serving a 10 years sentence and I sincerely hope they’re 10 loooong, terrifying years!

YAESU SCREENS Grrr!

Over the years I’ve owned many Yaesu radios and I’ve experienced problems with three of them, where the LCD has developed a fault. In the past it’s been a case of lines appearing and obscuring the information behind. Or, crystals have fallen to the bottom of the screen!

With modern colour screens, I was kinda hoping all that was a thing of the past, but sadly, my FT3D started to develop similar problems. It started with a single line and has grown to a rectangular block.

The annoying thing is that this radio has lived a very sheltered life compared to some in my collection. I’ve got bruised and battered HT’s from Quansheng, Wouxon and Baofeng which still have perfect screens. How come their screens remain good?

 

 

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RADIO OR…..

When you have multiple interests, it’s not easy to fit everything in and I personally find myself focusing too much on one hobby - usually radio! But recently I’ve been forcing myself to spend more time on my second love - painting!

It’s all too easy (and pleasurable) to pick up one of my lovely transceivers and go play radio in the great outdoors - especially on a lovely summers day. Or maybe experiment with the build of a DIY antenna. For sure, radio is my best friend, but I should not ignore my other lifelong friends.

And so I have been doing a lot of sketching and painting. I’ve focused on local scenes and have found a renewed interest in this hobby. I’m not very talented (I’m like the M7 of the painting world) lol, but it’s all about experimentation and learning. And fun! 😊

 

FAULTY VFO DIAL?

This post is to hopefully help beginners who are experiencing trouble with their dials! That could be your VFO, your volume knob, or virtually any other potentiometer or encoder that is not behaving itself (except optical encoders).

I noticed that my VFO dial on the ELAD FDM DUO was operating perfectly when turning clockwise but not anti-clockwise. It would either do nothing or it would tune down very erratically (sometimes even going up in frequency)! I also had a similar problem with my BELKA DX, so I dug out my can of contact cleaner and gave the dials a spray.

So what makes encoders go rogue? Well quite often it will be due to oxidisation on the contact surfaces or dirt and sometimes even moisture from condensation. The latter is especially true if your equipment is kept in a location which might be at risk of damp or moisture. My Belka DX for example spends a lot of its time in the glovebox of my car, where temperatures can quickly change from freezing cold to very hot. Some people have their shack in an out-house or a garage where humidity levels and temperatures can change significantly.

Whatever the reason, once a dial starts to malfunction, you need to do something about it - and it’s often extremely simple to get things back to normal. Buy a tin of Electrical Contact Cleaner and choose one which has a thin application-tube.

Remove sufficient panels on your radio to access the faulty switch and apply brief squirts of the contact cleaner to the switch’s moving parts. Some older switches will have their wafers open and visible, but most will be enclosed. Direct the spray to the part of the switch which will result in the cleaning fluid running down to the internal wafers as shown in the example below…

Spin the dial backwards and forwards (clockwise and anti-clockwise) to help spread the cleaning material across the contacts. If the dial also has a push function, be sure to work that too. It may require multiple applications depending on how bad things are.

Try not to get the spray all over your radio internals by covering open areas. And before operating your radio, allow time for the spray to evaporate and dry completely before powering up.

The encoders on both my radios now work perfectly and it only took a few minutes to complete the job.

73, Tom, M7MCQ.