SOTA Activation of Plynlimon During Storm Desmond

Here’s my wind/rain sodden 2m FM activation report of Plynlimon-Pen Pumlumon Fawr (GW/MW-001) last Friday while Storm Desmond was battering the UK. Bad parts were extreme wind and horizontal rain, good parts were 7+3 SOTA points, 3 summit to summits (S2S) and 1 SOTA complete!

Video is included.

73 James M(W)0JCQ


The sky here in France has turned from a glorious blue in Avignon this morning to something resembling your grey skies as I travel north back home. A gentle reintroduction to December weather after 12 days of sun and mild temperatures.

Currently about 200km north of Lyon travelling 320km/h on the marvellous TGV and I still get silly megabits/sec on my phone. Gotta love technology.

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Hi James

Thanks for the link to your report and the s2s from MW-001…nice summit when the sun is shining :slight_smile: . I have uploaded a report of my activations with Matt G8XYJ and a recent visit to the Aberystwyth ARS to my blog

73 Allan GW4VPX

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Thanks Allan, it seems like you and Matt had nicer WX for your activation :smile: I must have just missed you from my second summit that day, I think I packed up minutes before you started at 3pm!

Out of interest what linear do the both of you use?


Hi James

It’s the MX-P50M HF power amp for the FT 817.

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Thanks Allan, I’ll take a look. It looks pretty solid!


Just wondering what Power source do you use to power your 817 and this amp?
What kind of operating time do you get?


Hi David

I use a 9Ah Lithium Ion battery from Clulite

Tracer also make a similar one

Not really timed how long it lasts on an activation but I know that many times I’ve been using it for over an hour on ssb…long enough for my visit to a summit :slight_smile:

73 Allan GW4VPX

H James and David

Allan was the first person I know to use these amps, so after speaking with him over email I finally took the plunge and ordered one. I used it on Friday the 11th of December on G/WB-018 for the first time, I fired up on 40m and had about 40 QSOs in about 20mins with SSB. Was going to do 20m but could not self spot as my phone decided to have an off day.

Most reports were 59 or 59+, however I did not try the 817 on 5 watts only, so it is not a very good way to compare the results. Allan will be the better man to answer that question.

In terms of set up

See the photo below.

The 817 is powered via a Lipo 2.2ah 11.1v 3 cell battery with the 817 set on 2.5 watts.

The amp is powered via a Lipo 5.0ah 14.8v 4 cell battery, producing in the shack to a load (45 watts).

The package comes with an ACC line for the PTT of the 817, so you don’t need to worry about RF sensing for switching the amp on. However my only complaint is the wire is rather flimsy for this application and will eventually fail in my estimation.

I was worried about running it withe the 4 cell battery, this is because when they’re charged they’re normally over 15v, however after reading the blog and the comments of the below link, he says they’ll take 24v (Don’t know if i fully believe that). My father is a retired Transmitter Engineer of 43 years experience and he seemed convinced that my 15-15.3v would be OK, I am pleased to say he was correct!

Finally, here are the batteries that I use.

I would imagine the bigger battery would handle both the 817 and the amp, however i like the flexibility that these offer compared to the additional weight of carrying such a small 2.2ah lipo around.

Hope that helps


Matt G8XYJ

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Hi Matt

John G4YSS has been using one of these amps for a very long time (see his activation reports on this Reflector). On my activation yesterday I did not use it for 60m but switched on for 40m due to the contest…I think it did the trick for the chasers…the question is would they have heard me without it in the QRM…interesting ?

73 Allan

There’s actually WiFi on the TGV (but it’s not free unfortunately). Slowly, I think we’ll see WiFi available on more and more modes of transport. It’s even available on some ski slopes in Austria and Germany, but what ON EARTH is someone thinking, using the Internet while skiing down a mountainside!!


Thanks for the detailed information (and links - very handy)
I can see the sense of 2 separate batteries.

I normally operate QRP but would like the option of a bit more
power (sometimes). I have missed potential S2S previously running QRP
(just not heard)


Sorry David…forgot to mention…I use a 4Ah LiPo to power the FT817 so the two systems are separate.

73 Allan

I have a good contract in the UK in that my provider (Three) offers free-roaming in some countries. Instead of having to pay extra charges for roaming, when in France my phone connects to a French network but behaves as if I am in the UK and data and calls come out of my UK allowance. The result of that is there is no financial penalty and no need to do the “wifi desperado shuffle” where you scour the area for free Wifi. I used the phone in free-roaming mode in Lanzarote for 7 days and France for 10 days without question and only managed to consume about 550MB of my 2GB monthly allowance. I was getting HSPA access nearly everywhere in both Lanzarote and France and regularly saw better than 5mbps connection speeds. OK that’s a lot slower than my home 152mbps network and slower than 802.11n speeds the phone Wifi will do. But it’s wonderfully fast enough and free (well pre-paid).

The only issue is tethering is actively blocked. In the UK, tethering is technically outside the contract terms but accepted by the provider as long as you don’t abuse it. So I regularly use the phone as a modem, either via Bluetooth, USB or as a Wifi hotspot. But when abroad if you try any tethering you get a polite but firm warning saying you are getting free-roaming so please be nice and respect the rules.

I’ve used it France, Switzerland and Spain (Canaries) this year and it just works effortlessly. If only they would make it work in Germany too. This year at Friedrichshafen I bought a prepaid German SIM which came with GBs of data and put that SIM in an old burner Android phone and used that as a Wifi hotspot. The SIM stays active as long as you keep the phone connected to a network. So since June, the burner phone has sat in the shack powered up and has roamed onto a UK network. Should still be OK for next year with plenty of data left :wink:

Thanks for the info Matt. This little amp is tempting, and really really small compared to the already small 817!

Only thing that puts me off is I already have the 857 for QRO, so this would only be of use to my 817 and KX3. That being said the combined weight of 817 and amp is still less than the 857 :smiley:

73 James M0JCQ

I know your question was rhetorical, but if someone IS checking their internet while travelling downhill, they would be wondering how many Likes there last photo has got in the last 30 seconds. Instagram, Facebook, whatever. Nuts.
I’ll just go and check my facebook page, bye.


Hi James/ Allan & all,

Well done on going out in such rotten WX. You are obviously very enthusiastic which is brilliant.

On the subject of amps. I am currently using the MX-P50M and have given it a fair testing both in the UK and abroad during 2015. The amp weighs 513 grams and the leads another 70gm. (My Sainsonic MX-P50A weight is 1.12kg plus 0.1kg for leads etc).

Bench testing on all bands concluded that the MX-P50M more or less does what it should (as did the MX-P50A which is now on the shelf). For SOTA I normally use an 11.1V, 6Ah Li-Po to power both the amp and the FT817 in parallel. However I have added separate circuit breakering/ rev. pol. protection to both DC input lines - the amplifier has a 10 amp and the 817 a 2 Amp resettable circuit breaker. That’s maybe overdoing it. One fuse would do both but the 817 already had the 2 Amp breaker and it sometimes has to work on its own. The system is also OK with a 2.2Ah battery which I sometimes take as backup.

I have no absorption Wattmeter but I transmitted into a dummy load via my cheap (through) wattmeter, setting the meter to 50 Watts (FSD) with 13.8 Volts applied and an FT817 drive level of 5 Watts. Reducing the drive level to 2.5W; 1W and 0.5W produces readings of 36W; 15W and 5W respectively from the amplifier. These are the results for the 14MHz band and I set the 817 to FM for convenience. Other bands give similar results - maybe a bit less on 28MHz?

A 50W output drops to 33W when the input voltage is set down from 13.8V to 11V. The 817/ amp combination still produced a useable output at 10.2 Volts but it was zero at 9V. Where Li-Po’s are concerned that is a safety feature. Typical input current for the combination is 7.6 Amps at 11.3V. The amplifier was briefly transmitted (on 80m) with 5W input at 13.8V into an open circuit three times without damage. It was pleasantly warm (not hot) after completion of the test schedule which had many (albeit brief) input voltage/ RF drive/ frequency band combinations.

Unlike the MX-P50A, which has automatic band switching when used with the FT817, you need to manually select the required LPF on the MX-P50M front panel.

Selecting the wrong filter has no detrimental effect. If a lower filter than the band in use is selected, output is greatly curtailed as expected. If the filter is higher than the frequency of RF coming from the 817, the power output reading increases somewhat. Either that is due to harmonics getting through to the power meter and dummy load and adding to the reading or the filters for each band start to cut off too close to the band in use when the amp is properly set.

Though not specified for the band, the amplifier does function apparently at full power on the 160m band. However on 160 the 2nd harmonic is not filtered as the lowest LPF which can be set is the 80m band one. A separate (external) LPF would be needed for Top Band.

If you switch the linear off, the FT817 output still reaches the antenna OK via the receive path (HF). That would need checking if VHF / UHF was being used with the linear still in circuit and switched off. The path through the amp, though presumably direct (apart from relay contacts), might attenuate higher frequencies? To get around this I use the rear SO239 connection for HF and the front BNC connection for VHF on the FT817.

I agree about the flimsy PTT connection system between the amp and FT817.

The MX-P50M cost 139.95 GBP on Ebay in early 2015 but there was no instruction sheet or manual. It is smaller and lighter than the Sainsonic MX-P50A which in my opinion has a heavier heatsink than it really needs. (I did a lightening exercise on that one which got me close to 1kg all told.) After that, the MX-P50M (at not much more than half a kilo) was a ‘must have.’ The MX-P50A cost 154.59 GBP from Amazon in 2013 but I can’t find them for sale anywhere now.

Though the interconnection system is tailor made to fit the FT817, the suppliers of both these linears seem to imply (rather vaguely) that they will work with (5 Watt) rigs other than the FT817. I’m sure they would if an interconnection system could be devised for each different rig. You can short two pins on the rear connector to put the amplifier into the transmit state but research and work would be required to make that automatic when using other rigs.

I like both these amplifiers, especially the smaller and lighter MX-P50M. Weight saved when compared with my lightened IC706-2G is over 0.5kg and I don’t need the Icom’s extra half ‘S’ Point very often. I often employ an FT817 drive level of 2.5 Watts. That saves battery power with full power in reserve for more difficult contacts. I tell people I’m running about 30 Watts - near enough. That said, I have used it with a 5 Watt input for an entire activation in summer without problem.

It did ‘appear’ to fail near the end of an activation of CT3/MI-004 so I bought a second MX-P50M on return to the UK. However, when bench tested, the first one worked perfectly and continues to do, so I now have a spare. I must have dreamt the failure??? Perhaps it was just the battery voltage after all.

The above information is based on simple tests and observations at G4YSS and on SOTA’s and is for reference only. I do not have the kit (or the inclination these days) to do more exhaustive testing.

John G4YSS

Above: FT817ND and MX-P50M active on CT3/MI-001 2015 (G4YSS)

Above: FT817ND and MX-P50A active on EA8/LP-002 2014 (G4YSS)

Thanks to G4SSH in bringing my attention to this thread.

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Hi John

Thank you for your comprehensive and informative input into this thread. I had a feeling that it would not be long before we heard from you so thanks to Roy for letting you know. So far like you I have found the MX-P50M to be quite robust as I to have mis-treated it on a few occasions :slight_smile: Your various tests produce results very similar to mine and I was very interested in your battery set up. This is an area which I need to look at again and experiment with to lighten the load.

Thanks again John…no doubt Matt or James will pop up with a question.

73 Allan GW4VPX