I can recommend the inline speech compressor for the 817 family radios. I bought a DYC 8x7 at Friedrichshafen (I think Ed was there when I punted) and it makes a big difference. I did have to fiddle with the level pot on mine (listened on another radio and tweaked for max smoke/minimum distortion). Tests show that it can make a signal that you would only listen to just to get the summit ref and report into a signal that it’s possible to ragchew with not much effort.
I think the design of the compressor is slightly flawed - it is difficult or impossible to set the output level to match the level of the unamplfied/compressed microphone, so a test for compressor on/off is never fair. The pot controlling the output of the preamp is effectively a compression level control and the second pot is… the (other) actual compression level control, which changes the compression level internally in the compressor IC. The difference is probably seen when there is background noise, which will be too high if the preamp output is too high, negating the noise gate function somewhat.
I turned the amp gain pot down to about 25% and then set the compression level so I could hear the difference in a receiver without wincing at the sound of the audio…
Hi Matt, I use a similar HF amplifier that you can buy either as a kit or ready built board out of China - the same board is sold as both a 70w or 100w PEP output board (depending upon supply voltage). This one you have to add an LPF board to and put in your own switches and a case etc. So not as simple to get going as a MX-50. Getting back to my point, on CW mode - key down with 2.5w of drive gives 70 watts carrier out (so at least 100w PEP) on 40m (less on 20m etc). So i think you may find you need to set the drive to 1.5watts to keep the output under 50w PEP. This will also depend if there is an attenuator on the front of the amplifier of course.
Good luck with the Advanced test when you get to it. as someone who took the C&G RAE back in 74 I never went through the steps - the exam was the exam and needed about 6 months of training - which if you look at the three levels of UK licences is probably about the same time needed there.
As regards SOTA you won’t be running move than 50 watts in any case, as to make any noticeable difference you’d probably need to go to 200 or even 400 watts and the extra battery capacity and larger components in your antennas that you would need would be restrictive.
The jump from 5 or 10w to 50w is the major one for portable operation.
73 Ed.
Cheers all for your input . I may try the speech compressor first and see how I get on . Is it pretty much plug and play ?
When going inside a radio I’m pretty clueless so I leave it to those who know what there doing when comes to adjustments with pots etc .
I will be running the 818 of a 4s lifepo4 which I have started to build from 18650 cells . Will be 12.8v . Not sure on the ah as all the original wraps on the cells was removed but I know they was more than 1200 mah so at the minimum will be 4.8ah . Will be charged with a hobby charger at a charge rate at 2a .
Matt 2E0FGX
Sadly not. When in series, the capacity is that of the smallest cell, so 1200mAh in your case.
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Hi Matt
This may help.
Loads of info on the operating voltage vs output of the MX50 amps.
73
Tim G4YTD
The one Andy is referring to (available from SOTABeams as a kit or pre-built - Speech Compressor for FT-817, 818 - SOTABEAMS) is a dynamic speech compressor which goes in-line with the FT-817/818 microphone. Plug its cable into the microphone socket and the microphone lead into the other end of what is about a lipstick sized box. Power comes from the rig. you will only need to open the box if need to adjust the units settings for compression.
73 Ed.
The 3S LIPO 2500 maH 14 GBP battery from Hobby king ( https://hobbyking.com/en_us/turnigy-nano-tech-2500mah-3s1p-5-10c-transmitter-lipo-pack-futaba-6ex-and-3pks.html ) fits into the battery bay of the FT-817/818 and will run the rig at 5 watts out for a couple of activations without problems. You may want to take a look at that approach rather than having to carry an external battery?
Take a look at FT-817 Low Cost Lipo Battery | VK3YY
73 Ed.
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4 cells in parallel to up the ampage and there will be 4 banks of parallel joined in series to up the voltage Andy . 16 cells I have got
Matt
Adjust compression is that in the speech compressor itself or in the radio ?
Am I guessing it comes with instructions?
Matt 2E0FGX
In the little black box itself - you must not have compression turned on in the FT818 if you have an external speech processor. Does the FT-818 have built-in compression? If it does it isn’t very good - most compression options except in the more expensive radios, tend to be bodges in the audio stages and create more “splatter” than “punch”.
Any setting in the box is a “set and forget” though. You need to set it to suit your voice and then leave it.
Here’s an article (in German and English) on it http://www.sotabeams.co.uk/content/817COMPRESSOR.pdf
73 Ed.
I got an Ft-891 to avoid the 817 plus amplifier issue and gain a newer receiver and 32bit DSP
So I can roll out 5 to 100 watts without any cables to worry about
Yes the current drain is more on receive but its worth it
Just pack a bigger battery
John ve3ips
Yes there cracking radios and the dsp work well . But I wanted a lighter radio with vhf as well as hf so was only feasible choice. Not done summits like snowdon yet but imagine that be a vhf activation
Matt 2E0FGX
That’s known as a 4S4P setup Matt. Yes, then it will have a capacity around 4x the single cell capacity.
…and lose 2m and 70cm! A pity, its such a tempting little radio.
I believe not - but it is worth remembering that the FT857D does have a built in compressor which I find very effective. Its one of those things that you tend to set and forget about, so beware of adding an external compressor too!
My wife and I are both participants in SOTA. She is strictly phone while I am primarily CW. We have had summits where she barely made the four contacts needed due to conditions.
I purchased one of the MX-P50M amplifiers and did a few bench tests. The device used for amplification is robust and capable of 100 watts at 900 MHz. The output is clean as long and you have the band switch set to the correct band. It functioned from 10 to 15 volts, the PA could take more voltage but I wasn’t sure about the rest of the circuit. The output power using 5 watts drive, varied from 35 to 45 watts, depending on voltage and bands.
We take it up on the hills and she now regularly makes 10 or better contacts. We use a 6 Ahr LiFePO4 12V battery, which seems to be all we need, so far we have activated three summits on one charge and the battery had plenty more to offer.
So far 70+ activations and no issues.
By the way, there is a SOTA Reflector thread with how to connect the FT817. FT817 + 45w Amp cable info needed
Lee N7LP
That’s the view from north of the border. 
My opinion is that they are a worthwhile buy. I use mine with both my FT-817ND and IC-703. The main problem with building your own amp is sourcing the components for the filters. Quite frankly I would rather spend my spare time on the hills, not trying to build an equivalent of this amp in so small a package with eyesight which is not what it used to be.
Well I found a UK source on eBay. I did note this is another thread some months back.
As for the power source, I run mine off a 4.2AH 4S LiFePO4 and at 2.5 watts drive I get around 30 watts out depending upon the frequency. That gives me at least 3 hours operating time. I agree with Malen that 30 watts out is the sweet spot for battery life / QSO’s. In practice it does actually make a difference when running SSB relative to an 817 barefoot and as Andrew says a speech processor is a worthwhile addition. The downside of running an external amp is the additional cabling. I also have the FT-857D which is a much neater solution, but it is less economical in terms of battery power.
If i need to do the vhf/uhf bands I pack the 817 or a handheld to use along with the 891. However, for car to summit then the weight is nothing to worry about and I can also bring a ladder and a picnic table.
If I was being a ultralight then I would use the 817 or the MTR3B and a handheld
Depends on the summit but why pack another amplifier and cable set
John ve3ips
Not very nice Brian, I might refer that remark to the Moderator.
CW was but one of seven approaches I suggested that I consider to be very much preferable to a linear amp. I think that’s a perfectly valid point. You even agree with one of my other suggestions but trust you won’t attract a similarly sneering remark!
A linear amp to me is extra weight, extra volume and extra expense, as well as denying oneself all the fun and satisfaction associated with each of my suggestions above.