The power output from the MX50P is claimed as 50w and I never achieved quite that from mine. I found that more than 2.5w was too much drive and that would cause splatter - a wider than acceptable signal on SSB - and would waste power on CW.
Just a thought on the 70w/100w issue. PEP means the peak envelope power of a complex waveform but CW is a steady carrier. The peak power is equal to the average in that case. For a two tone test there is a standard relationship between the average power and the peak power over a modulation cycle. (Working from memory - can’t recall the number). For voice there is no standard, but the average power shown on an average reading meter is about 30% of the peak envelope power (on a sustained voice sound ). Eg. on my Emtronics ATU the power meter usually indicates a peak reading of 20w when the radio is actually producing 100w peak. That’s normal and any higher readings will only occur with speech processing or overdrive.
I’d be suspicious of a power measurement so far above the rated power of the amplifier. Does it gel with the DC power being consumed and still have an efficiency of about 50%. (Power out divided by DC power consumed)… if not, check the power measurement device. Hope this helps…
OK for Matt then if the MX50 tops out at 50 watts. I also made the point to be careful with drive levels. All these Chinese amplifiers seem to require only a low drive level (certainly not more than 3 watts) for full output. That is unless there is an attenuator on the input to drop the power of course.
I don’t have a PEP reading power meter. I have an SWR bridge with an “average” setting on it, but I wouldn’t trust that. When CW is generated correctly by inserting a carrier, the reading is as you say but if CW is created by generating an audio tone on one sideband - how does that relate to the power readings displayed?
In any case, whether an amplifier creates 40, 50 or 70 watts PEP output the difference in signal strength at the receiving end is only going to be marginal.
My amplifier kit (not sure about the MX-50) uses a pair of PA transistors in push-pull in AB1 mode I believe.
Heading out for an activation - wish me luck with the weather! (it doesn’t look good at the moment).
73 Ed.
The only mod I did was to change the PTT cable to a Phono as opposed to the one they supply, I did this as when on holiday, I take the 817, a small netbook and the Amp. If you use the amp you cant have CAT control for the 817, unless you buy/make one of these- Phono are more common than the supplied connector, so it offers greater flexibility
Now I can use it both for SOTA with no CAT or at home/on holiday with CAT Control
They get really warm on the full cycle modes like FT8, infact it is worrying how hot they get, but on SSB they’re fine.
I power mine with a 5ah 4cell Lipo- seems happy enough at 14.8v. The 817 is powered from a 2.2ah 3 cell Lipo
I use it on 60m, but make sure the 40m band is selected so as to negate any harmonics - I believe Allan GW4VPX does the same.
I also use the Speech Compressor from Germany that is built into the Microphone, I think you can buy one that goes inline with the Mic Connector. So I can get about 45 watts with some good punchy audio on the hill.
Having said all this, I still find myself on VHF more and more, tried the HF on SOTA and just saw it as a waste of the height!! If you’re up a hill, get on 2m with a beam and you will generally qualify and simplify the set up and speed of setting up!
Hi Ed, it all depends on the actual waveform. If there is a carrier on one frequency, even when achieved by inserting an audio tone, as long as the carrier and opposite sideband are suppressed sufficiently, the signal is near enough to a single frequency and the cw power reading can be taken as real.
I don’t think any current radios from the big three or four transmit cw using audio tones. That situation is more likely to occur when using an ssb mode to transmit some of the digital modes.
Thank you all lots of great information in this thread . My idea is to use the linear for /p as well for sota activations . I got a holiday booked to go to lundy island in the bristol channel next summer and staying in a 1 man cottage . And will be taking radio kit as well as going exploring around the island . I have a 16ah lifepo4 golf cart battery which will use as well being able to charge during the day when the power is on .
This is the pack I have started to build a lifepo4 18650 pack from cells I had from a battery where the bms went wrong along with some of the cells .
I finally found the time to make a report on my build of the Chinese amplifier kit advertised as the “DIY 70W amplifier”.
I only had to pay for the amplifier kit, and the toroids for the LPF’s, the rest I found in my junkbox, total cost was below 20$!
I wanted to run it off a 3S6P Li-Ion battery pack I made (looks a bit like the one above), so I don’t get 70W … rather 40-50W, depending on band and battery voltage. But it works great, and it is linear(-ish) …
It lets me run my KX3 a lot cooler at only 2W drive power.
I hope to use it with the ATU-100 autotuner I described earlier on the Reflector.
Something is wrong here I guess.Solar minimum is not exactly a good argument to use a power amplifier, the reason is simple: the amplifier will not make the signals of the chasers louder. Except if you have the idea that all chasers are using 1 KW to chase.
It is solar minimum and I chase SOTA with equipment similar to an activator: qrp and a 3m long milwhip antenna, so far no complaints in filling my SOTA log.
It is my idea that I chase on the same level as the activator, qrp + simple antenna. Is this an error of judgement? I hope not?
Might be that in the future SOTA will have to upgrade the rules for activators with putting a maximum on the power used??
You make an interesting point of view. As I understand it, something can only be fun and rewarding if it is easy?
I wonder what is more difficult for an activator, dealing with a rather weak signal from a qrp chaser, or dealing with being called by a group of QRO stations who do their best to overpower each other.
QRP? I recall a youtube film from HB9BNG making contact from Switzerland to New Zealand with qrp ssb from a summit January 2020, so in the middle of solar minimum.
It’s an interesting question. But not relevant to the SOTA awards programme.
The decisions of what band / mode / equipment / power to use are entirely for the participants. Many of us do indeed challenge ourselves to do something different, interesting, demanding etc for our own stimulation and sense of achievement. But the only rule is to use what your licence permits you to use, and this will not change.
Like so much in amateur radio, it is what you want it to be. I operate QRP while chasing most of the time. If I can’t get through, then I turn the RF up to the 15W max of the KX3 – that’s all I have. There’s few times I can’t get through.
While activating, I’ll run my KX2 at 12W, because I know my aerial is a compromise on anything other than 20m.
As long as you aren’t too frustrated by your setup, I wouldn’t worry too much about it.
The more QRO either the bigger the battery or the shorter the activation. The bigger the mast (and probably the more efficient the antenna) the more stuff to carry up the hillside. Its all a compromise and there isn’t a right answer, a right output power, the right band or mode, which for me is what makes it fun. I must admit that I like to have the kit with me to make 4 contacts fairly quickly as I am usually pushed for time even if it means a bit more weight on my back. My main challenge is often the climb up the hill!
Everyone’s different, but this wouldn’t be my view Patrick. If something is too easy, it risks being boring or routine. I get more personal reward from something that is a bit of a challenge (however, too much of a challenge can become frustrating).
Hi Luc, Yes to get the full output of these amplifiers (70 or 100w depending upon model) - you need to run them on 16V - so a LIPO 4S battery.
I’ve found any more than 3 watts drive is not necessary, so an increase for 3 watts to even 40 or 50 watts is a big jump.
There are now some new kits quoting 180 or even 200 watts output but I suspect they will really kill the battery when portable! The increased signal over the 70 watt model is less than one S-Point in any case.
73 Ed.
UPDATE 29/10/2020:
Similar Chinese amplifiers that use the same PC board. Some using a power module rather than the two power MOSfets (mounted in the same place) are now advertised as kits or ready built producing either 180 or 220 watts - some need a 24v DC supply at many amps I expect. Some claim 180watts at 13.8v. I can’t see these being intended for “backpack portable” - more likely for shack use as they are sensitive to bad VSWR. Interesting that it’s still the same design, however. https://www.ebay.co.uk/itm/180W-Linear-Power-Amplifier-Amp-Kit-For-Transceiver-Intercom-Radio-HF-FM-Ham-SZ/164293911961? MiNi 200W HF Power Amplifier Shortwave Power Amplifier Unassemble | eBay?
Perhaps it’s good timing that the cheap spectrum analysers are now available out of China - to look at what off-frequency signals these higher-powered amplifiers are producing?
It’s also against the basic SOTA principal of inclusion. As long as the activator does not exceed the power allowed in his or her licence, it’s up to them if they want to carry the extra heavy batteries, heavier antennas, thicker co-ax etc. up to a summit to be able to run high power.
My experience is that as a general rule, at least on SSB, chasers do tend to be running more power than the activator.
SOTA does not equate to having to run QRP. Many activators do run QRP and enjoy doing so, and good luck to them. I myself have worked S2S into VK several times on 5 watts or less of SSB when conditions were better and around Europe and Scandinavia since. It is a thrill to mange a DX contact on such low power, but of course the QRPP operators will say 5w is QRO for them.
It’s what you enjoy and your personal achievements that matter.
). Eg. on my Emtronics ATU the power meter usually indicates a peak reading of 20w when the radio is actually producing 100w peak. That’s normal and any higher readings will only occur with speech processing or overdrive.
