Hi all, I have scrolled through the reflector to try and find an answer to my question, but cannot see any?
Has anyone used this amp on 5MHz (60M) and if so did you use the 80m rotary control button??
Cheers Tony
Go for the next band up.
This worked OK for me on 60m.
2 Likes
I haven’t used one of those, but on my HF Packer Amp you use the 40M filter selection for 60m.
This is because it’s a low pass filter and so you need to use the next highest frequency filter, i.e.7MHz for 5MHz, if you select the 80m (3.5MHz) filter then 5MHz will be above the cut-off frequency and it won’t output any power, instead the filter will soak it up and get very hot.
4 Likes
I have used it on 60 with the switch at 40m - ( I believe it is a low pass filter ). The only issue I had was possibly over-driving it - I got a report of being a bit “wide” and since then have made sure to drive it with 2.5w not 5w. Found this useful MX-P50M HF AMPLIFIER REVIEW. | VK2QR Adventures in Ham Radio 73 Paul
3 Likes
Brilliant Thanks for the info guys, and especially the overdrive heads up Paul, will Lower my output on my KX3 before the 17th!!
Best 73 Tony
2 Likes
Can confirm that my MXP50 requires only 2.5w to reach 40w output, any more input and the output does not increase, which is a sure sign compression and flat topping will be occurring, your signal will be spreading out over the band, not only bad operating practice but also pointless as it does not increase the signal in the other guy’s receiver.
I haven’t used it on 60m as we don’t have that band, but I have accidentally used it on 3.5 with the filter set to 40m. It is a low pass filter, it is for filtering out the harmonics generated by the amplifier and hopefully complying with spectral purity requirements. It does not affect how wide the signal is “in band” you can only improve that by reducing the drive level from your transmitter.
If you usually use your ATU in the radio, eg in kx2/3, it will not be doing its normal job as the ATU is not connected to the antenna when the amplifier is in circuit. Make sure your antenna is a good match for the amplifier. An ATU following the amplifier may be required.
There is some concern about the relay switching of the MXP50M series. It apparently does not have a protective diode to suppress negative spikes on the relay power line from the radio. Some users have installed a negative spike protection diode in the amplifier to protect the keying device in the radio. I didn’t do that when using it with an FT817, but if I resume doing that, I will install a protective diode first.
73 Andrew VK1DA/VK2DA
4 Likes
Interesting. Mine, out of the box gives 4x gain.
e.g. 5w carrier in produces 20w out measured with the same power meter into a dummy load.
I was surprised by this low gain at first and did find a page (or was it video?) claiming to detail how to adjust the gain. Which I never did try. But I can’t find that webpage now, so …
Anyway, 20w is enough for me, and gives a good balance of battery use between the FT818 and amp (both go flat at same time under typical use). But I’m intrigued as to why I see lower gain than others report.
re 60m - I use the 40m setting. 2.5w on the ft818 gives 10w out for me - same gain as other bands, which keeps me under the ZL power limits for that band.
1 Like
I did not bother with the diode (ignorance probably) with the FT817, but I did put a diode in the control cable when I use it with the KX2.
I turn the amp off to check the SWR before putting it in the circuit - that way I’m not putting into an unknown match. (I have had the odd fault on my wire antennas - which is probably to be expected when they are regularly bundled into a rucksack…)
Paul
1 Like
I check the antenna SWR before plugging the amp into the radio. I believe the amplifier doesn’t have any decent SWR protection built in.
Does a high SWR still show up if the amp is turned off but still in circuit?
2 Likes
I believe so - the SWR meter on the rig just indicates 1:1 with the amp in circuit but it does show a “different” reading when turned off - so I have assumed it is bypassed by a relay - as it would be on recieve.
2 Likes
I use mine with the 817 set at 2.5w output and get around 25 - 30 watts out depending on the frequency. If I drive it with the full output of the 817 I get around 40 watts out. The additional battery consumption is just not worth it. The way things are, I’m starting to wonder whether the amp (with the 4.2AH LiFePO4) is worth carrying under normal circumstances, especially on the big hills. Having said that, it did help me to bag 18 on 30m CW last Thursday whereas I might have struggled with just the 817. Some incoming reports were marginal.
2 Likes
I’m with you on that Gerald @G4OIG . I’ve carried our amp on many occasions now, but we simply haven’t used it. We can only go up to 10w anyway with Nic’s M7 licence, but I guess it’s nice to have it in case the contacts are marginal and 10w would help. I’m itching to buy an Elecraft or IC-705 for the same reason, but given the success we normally have with the FT-818 on 6w, I can’t warrant the expense…
Even on Orkney and in the wilds of Scotland, we haven’t used the amp. The only time we really wanted a bit more oomph was doing The Cloud a few weeks ago. I guess the demand for a 1 point chase isn’t quite as high as when we activate a rarer 8 point GW/NW summit 
73, Simon
3 Likes
…must admit that since getting the KX2 the amp isn’t used very much. The extra weight of the battery, the amp and the lack of an ATU have all been factors. It seemed to make a bigger difference with the 817 ( Not surprising really as it had half the power and no speech processor…). 73 Paul
3 Likes
The outboard compressor I have made a noticeable improvement for SSB on the 817. I doubt the 3dB makes much difference for CW.
I’ve used and add on PA when in exotic parts (EA8/GC, EA8/FU) of about 25W. Both times old Sol was in his slumbers and predictions from there to the EU/NA didn’t look brilliant. Running 25W on 20m CW from Fuerteventura was quite worthwhile. I’d only carry such an amp now if I was going somewhere juicy and wanted to be a good signal. Otherwise not worth the weight and battery penalty.
3 Likes