In reply to M1EYP:
I know of a 10 watt mod, this probably affects all the power settings but I’m sure it isn’t good for the rig! However, coaxing it up to 6 watts with the next level down 3 watts should not be too risky. Mind you, I doubt that a chaser will note any difference between 2.5 and 3 watts! 
73
Brian G8ADD
In reply to M1EYP:
You can download the technical manual from my vast manual collection at http://www.moosedata.com/Manuals/Yaesu/FT-817_Technical_supplement.pdf and this details the whole alignment details. You should be able to adjust the 2.5W setting up to 3W but I doubt anyone would really notice any difference between the 2.5 and 3W levels.
Andy
MM0FMF
I doubt anyone would really notice any difference between the 2.5 and 3W levels.
…but someone I know who has done this ‘tweak’ tends to win any Backpackers session he enters (thankfully not to many hi!).
I guess it’s about attention to detail, and that is only one aspect of many fine details of optimising his portable station.
Maybe it’s not so much about noticing the difference - but about what ODX it enables you to reach.
I’ll probably stick to 2.5 watts though; it was enough to win the last Backpackers contest I did, and I have a masterplan/strategy for next year’s series - all based on my choices of SOTA summits for each session! This will be compromised somewhat by my preference of using a different summit for each session (rather than the best summit for all of them), but we will see. If I can win one from Gun G/SP-013, then the result should be assured from some of the summits I am considering! 
You never quite know though; some summits can be better or worse than you might imagine. Kinder Scout SP-001 or Black Hill SP-002 are never that good on QRP VHF, despite being the highest spots anywhere around here. The Wrekin WB-010 wasn’t as good as I imagined it would be in the 3rd Backpackers, given its lofty isolated position. Gun was good, and I do perhaps surprisingly well in the VHF activity contests from The Cloud G/SP-015.
Tom M1EYP
In reply to G4OBK:
Hi Phil,
Very interesting to read your thoughts about SLABs, LiPos, etc.
I use an FT-817 which produces just under 5w output on HF with an external 12v battery. You may be interested to know that I bought two SLABs from a company in Wales, www.component-shop.co.uk.
One is a 12v 9.0 Ah SLAB, which is exactly the same size and weight as the standard 7 Ah SLAB, but has increased capacity. Its weight is 2.6 kg.
The other is a 12v 3.3 Ah SLAB, which is about two-thirds the height of the 7 Ah version and weighs only 1.3 kg. I have run the FT-817 for several hours on the 3.3 Ah battery and have come nowhere near exhausting it! Therefore it is more than adequate for a normal day’s activation.
I have not tried LiPos. I am a little chary about them because of their specialised charging requirements and danger of fire or overheating!
73,
Walt (G3NYY)
In reply to G3NYY, G4ZHI
I have not tried LiPos. I am a little chary about them because of
their specialised charging requirements and danger of fire or
overheating!
Hi Walt, Bryn
LiPo’s do need a little care in their use, but the advantages far outweigh the aggro. Treat them right and they will give ample reward in perfect safety.
One factor generally overlooked in the comparison of SLAB’s and other technologies is the effect of discharge rate on available power. Uniquely SLAB’s are rated at a discharge rate of C/20, and available capacity diminishes alarmingly at higher rates. Although not too much of an issue with an '817, the more powerful rigs are more problematic. On receive alone an '857 draws 1 Amp, which with a 7Ah SLAB equates to approx. 0.15C. According to Yuasa’s figures for their NP range of SLABs at this rate the 7Ah battery will only deliver approx. 6Ah and that’s before you’ve started transmitting! Although quantitative data is hard to come by, battery life is also considerably reduced at high discharge rates. I personally wouldn’t consider using SLABs of a size I’d be happy to carry up hills with a higher powered rig.
Hope that helps…
73 de Paul G4MD
In reply to G4MD:
Hi Paul, many moons ago I had Yuasa SLABs, however when I switched from 817 to 857, I also switched to using Camden deep discharge SLABs. To date, after 600+ 857 activations the batteries are still performing well. I will eventually switch to LiPo technology, but I can see me sticking with these bricks a while longer.
From the yaesu 857 manual:-
Current Consumption: Squelched: 550 mA (Approx.)
Receive: 1 A
Transmit: 22 A
73.
In reply to G1INK:
Hi Steve
The Camden units look to be very much superior to the Yuasa NP’s. Wonder what capacity batteries you use?
Apologies for getting the current drain wrong - took it from some notes I made when doing the comparison some time ago, should have checked it. Original post now corrected, but I still wouldn’t like to start lugging SLABs up hills again!
73 de Paul G4MD
In reply to G4MD:
Paul, I use 7AH units. Normally sufficient for 2 hours at full output on ssb or 70 - 80 contacts. Shame to get rid of them - but LiPo is coming !!
I get 10 or 15 60min + activations out of my 7Ah SLAB. For an 817 running 5w, it is overkill! Very reliable though.
Tom M1EYP
In reply to M1EYP:
I suspect we’re all “sad enough to be interested” Paul.
OK Tom that’s sufficient provocation!
For my two examples of FT817ND what I found was that up to and including 24MHz you get more or less as much out of the rig as you’re going to with any supply voltage above 9V.
On 28MHz and above, a step change in behaviour occurs and output is approximately proportional to supply voltage, reaching a plateau at approx. 13V. Output for a given voltage also reduces with increasing frequency.
All tests carried out with external regulated supply on 5W setting.
If anyone’s seriously interested in the actual measurements, e-mail me privately and I could put the results into an Excel spreadsheet.
73 de Paul G4MD (paul underscore g4md at btinternet dot com)