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It's interesting that the noise floor has been around -93 dBm, with and without the first mixer post amplifier.? Will explore this some more.? I wonder if the log amp is setting the floor now. The

Hi Farhhan, I'll hook up my other spectrum analyzer today. It's a Texscan VSM-5D. Only 4MHz-450MHz, but that's plenty for this. HOWEVER, this test was without any amp. Just the uBITX feeding the Narda

The tinysa does not have shielding needed for a decent, spur free reading, at 40 watts of power it will probably read spurs even without connecting it up.

John, I wouldn't mind experimenting with a couple of the BLV 861 devices...please and thank you. K3BO Barry wrote:

As of 6/9/2021 10am most of them are gone a few are still available. BLF 861, 5 available BLV861 ...seems nobody wants bipolar transistors lol still 20 available BLF278 gone SRF3943 (MRF151) 2

My Chinese amp uses the good ol' (and obsoleted but widely available) MRF 9120. It works fine for me. Rafael

Ashhar, I would expect the effect - of the scope not being terminated - to be minimal, because there was a 30dB Narda attenuator between the uBITX and the scope. The Narda is rated for microwave, and

*** I don't really know. I think it was on 80M when the amp failed. But I *had* tested it on 20 in that session, and the RF voltage output on 20 was indeed much higher than the other bands. Looks like

Jerry, I would suspect the measuring instruments. If you have an oscilloscope, then parallel up 20 of 2 watt/50 ohms resistors as a dummy load and measure RF voltage (with bandwidth filter on our

Do you think this is the cause of the amp failing, or damage caused by the amp failing and sending some rf back into the radio? Max KG4PID

All, To help me post-mortem the Chinese linear, I was checking the output of the uBITX on various bands. I used a Bird 4410 wattmeter with the 10kW slug ( which can be switched down to 10W full scale

Yay! This also means that we cant do away with the post mix amp altogether... Maybe. We need 80 db of usable, distortion free range for good measurements. Let's see how we will get there. With 14 dbm

I was WN6EPS. It was a nice call - dit di-dah-dah-dit di-di-dit! The other day, I QSO'd a guy who was running a pair of Conar twins. Sounded just like the old days...Bwee bw-bwee-bwee-bwee. Chirps &

Birdies?? I've been a ham for over 50 years.? In one of my very early days I worked a WN---- (don't recall the rest of the call). The signal sounded like he couldn't find a key, so he was pulling

Hi John, Well, it was coincidentally on 80M when it died. And that is surely the band on which the uBITX gives the most output. But if that's enough to fry the finals, the amp and the uBITX are just

BLF861 16 BLV861, 20 available BLF278 6 available SRF3943 6 available SRF426 (Mrf426)? 4 available MRF150 gone MRF314 4 available MRF148 gone MRF450 2 available SD1480 gone

All very fair points.? I clearly misinterpreted an intention that wasn't there. You're right, it was.? I latched on to one word and ran with it.? As long as you're having fun with your radio the

*** Unsoldered the final transistors - one of them tests as a MOSFET, the other one as a 1.8 ohm resistor. I'm guessing the latter is the bad one :). There is another Chinese amp that uses a real RF

Jerry, Did you measure the input impedance to the changed low pass filter before you applied power through it? It might not present an impedance that makes the transistors happy. Also, given the

Hi Doug - no offense intended. QRP is fun. That's what ham radio is for - for me, anyway. Fun. But it's no fun when people don't hear you. And at my QTH, with my antenna, people mostly just don't hear