Hi Chris, thanks for your testing report. Very interesting.
73 de Geoff vk3sq
Hi Chris,
If you select an LPF for a higher frequency you are letting the harmonics and any mixing products from earlier stages in the chain through - hence the signal may still be 45 watts going out on 7MHz but you also have harmonics at every multiple of the frequency up to the frequency that the LPF blocks. - so most likely 45 watts on 7 MHz and 25 watts on 14 MHz. If you select the next LPF up you might even get some RF on 21MHz! The higher power output doesnât make your signal stronger on the required (7MHz) frequency. In fact if using a 7MHz resonant antenna you are creating SWR issues by using the wrong LPF (you may also get RF ingres/feedback into the equipment).
I run my similar Chinese amplifier at either 2.5 or 3 w drive - you might find you get the same output at a lower drive level (and perhaps a cleaner signal). The trick is to back off the drive to the point where the output just drops a couple of watts. Those 2 watts at 45 watts are not going to make your signal weaker but it will keep it cleaner.
Another point to remember - amplifiers are usually rated at PEP output but most of the SWR/Power meters that we use donât read PEP (even the PEP button on some of them is really an average reading). So when you see 40-45 watts output (with the correct LPF selected) on the meter - the PEP output will be closer to 65-70 watts. I believe using a two-tone generator on the microphone input is one way to get a more accurate reading but my ârule of thumbâ is that the indicated reading is probably only 2/3 of the PEP output. (roughly).
Sorry if some of this you already know much of this - but it may be good guidance to others reading this thread.
73 Ed.
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If you measure the transmit power with CW, the displayed value should be identical with PEP measuring mode.
73, Peter - HB9PJT
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I would second cautioning about power dissipation via the heatsink. This is likely to be the most obvious failure mode.
Hi Peter,
Thanks for the tip as regards simply using CW/FM/RTTY rather than a two-tone generator - This from WikiPedia.
## PEP vs. Average Power[edit]
PEP is equal to steady carrier power, or radiotelegraph dot or dash average power, in a properly-formed CW transmission. PEP is also equal to average power in a steady FM, FSK, or RTTY transmission.
Although average power is the same as PEP for complex modulation forms, such as FSK, the peak envelope power bears no particular ratio or mathematical relationship to longer-term average power in distorted envelopes, such as a CW waveform with power overshoot, or with amplitude modulated waveforms, such as SSB or AM voice transmissions. Typical average power of a SSB voice transmission, for example, is 10-20% of PEP. The percentage of longer term average power to PEP increases with processing, and commonly reaches ~50% with extreme speech processing.
The pertinent point for Chris in this text however is that SSB speech shows only 10-20% of PEP - a little more with speech processing. So in the end, the value that you see on an SWR bridge will not indicate the Peak output power. Except if Chris is a CW op rather than an SSB only one.
Good to know, that switching to CW (at the same drive level to the amplifier) will give you the equivalent reading to SSB PEP. A simple way to measure what the amplifier can produce. Of course, as mentioned before be careful with either key-down CW (testing) or operational Digital modes that the heat sink can handle the operation.
73 Ed.
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Thank you Ed (@DD5LP) for all the helpful information and your insights into the function of the LPF. The conclusion is to avoid to work with the wrong filter settings, which actually sounds logical. One must not be blinded with the output power that you achieve on 40m with the next higher filter settings. The amp really gets hot at this power!
The above power measurements were performed in FM / CW to achieve maximum output. As noted, for SSB one would require to measure âreal PEP peak holdâ, which only a few watt meters can achieve, such as the ones provided by Palstar, e.g. PM2000A. For testing the maximum output of an amp, however, it is sufficient to do this in FM or CW straight into a dummy load.
73 de Chris
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Hi Christian @DL1GKC,
I hope you keep well!
Iâve just been reading your above thread and wanted to know how long your 14.8v 4.4A battery lasts with the amp pushing a constant 45w output?
I have a 14.8v (16.4v) 5.2Ah Li-ion battery that I will be using and wanted to know would it last for two SOTA activations in the field being approx 20 mins of operating each.
73, Ben
GW4BML
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Just a bit of basic maths.
Itâs reasonable to assume a 45W amp will be about 50% efficient, so 90W consumption.
Constant output, so P=VI, I = 90/14.8 = 6.1A
The hard bit is just how the battery Ah rating is calculated. 5.2Ah doesnât generally mean you can draw 5.2A for 1hr, typically itâs at a lower rate, maybe 1/10th. i.e. you can draw 520mA for 10hrs.
Simple maths says 5.2Ah is about 51mins at 6.1A, but whether that is really the case depends on the battery itself. And, of course, the voltage curve is very non-linear on a Li-ion battery.
Maybe it will last for your use case.
p.s. Amps donât push anything.
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I was waiting for the mathematical answer 
I can work that out myselfâŚâŚ I want the actual in the field results, I will test next weekend and see how I get on. Thanks for the info though Andy 
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Iâve had over an hour out of mine running from an 11.1v (nominal) battery with 3.25Ah capacity.
I was probably only running it at 25W though (2.5W in).
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Thatâs what I needed to hear 
cheers @MW0PJE Pete. I have one in the cupboard that Iâm going to try. If I can get an hour out of a 14.8v li-ion 5.2Ah batt, Iâll be happy.
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