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I cut the track on two Rev. 3A units last night, receiver problem has gone, now works perfectly.? A blade was used and the result checked with a magnifying glass. These are a great little radio. Bob

Hi Dan, did you manage to find out? I am asking as I am having the same curves as on your 80 band, but I have it on all just not on 20. I think it could be something wrong with my low-pass filters, I

Is there a specific/recommended ptt cable to use between the QDX and the amplifier?

Andy: I am with you 100% on Anritsu menus! 73, Don N2VGU

I don't think that you are going to get to your answer with this approach. The key thing that I see is that the reflected power from the mismatched antenna is again reflected by the low output

I was trying to show the effect of both the DC dissipation AND reflections. If there are reflections in the case of 2:1 VSWR for example, does that power get dissipated along with the DC power from

I am using a DROKK switching buck/boost DC to DC converter.? It seems to work well, and I can adjust the voltage easily to allow for lower power output for things like the WA2EBY amp that I use to

Hi Dan & Randy, I copied Dan's Solution with a 7809. However, as the rig still got quite hot, I added a heatsink on top of the case (see pic) ... But still I do develop Temperatures around 50°C in

John, I'm not sure that's correct. The 5 W out is not the issue, it's the 3.3 W not produced as RF due to the 40% (or maybe a bit less) inefficiency as class D. The 5 W out is only an issue when or if

Thanks Hans, and everyone else, for your replies. I guess I was tempted by a less complex build.? The reality is that this is my biggest project to date, and you have all helped me to realise, to

So Daniel, as an example. If we produce 5W RF, and 0.56W is reflected (2:1 VSWR), we have 5.56W RF to deal with, in addition to the DC dissipation. Let's say we DO dissipate 3.3W across all four

Congratulations, you will have a lot of fun, just be patient. Terry? ?w6leo

And with four probably un-matched transistors (I don't know if Hans has that performed or performs it), there's probably uneven dissipation too. So from the over-voltage perspective, seems to be, keep

Or if you decide to try five, be pragmatic and consider hedging your bets by leaving room for an extra QRP Labs filter board. It will cost you nothing but space and a few extra chassis holes for now.

You might want to consider the Hermes Lite N2ADR filter board. Has built-in SWR bridge. $52.70 at Makerfabs. It's only rated for 5 watts however. -Steve K1RF

Hello Daimon As others have said, the answer depends a lot on your performance objectives. Assuming that you want to meet license regulations regarding spectral purity (harmonic levels) then you need

Back in the good old days when the world needed home grown RF Engineers, your employer or educational establishment would end up sending you on a day or weekend course on using measurement equipment,

My QDX smoked with SWR of 8 on the 60 m band.? I forgot my antenna was not resonant on 60m.? I've ordered the 4SQRP 4S tuner that has a VSWR resistive bridge so the QDX will never see >2:1 mismatch

John, If the QDX is about 60+% efficient, at 5 W RF out, you are putting nearly 8.3 W DC into the finals. That 3.3 W mostly goes into heat in the finals. If this is correct, then each BS170 is

Whence why we refer to power dissipation as well as the voltage seen across usually the Drain + Source of the FET's (we assume at this point that we're not using a common gate configuration). Of