开云体育

Has anyone succeeded with adding CW properly? I have seen several possibilities on here, but no working examples. If yes, how did you do it? Or is it just impractical, like making milk from chalk and water? I was planning to at least inject a tone from a simple circuit for antenna tuning. But I took down my friends G5RV jr. in favor of a better 40 meter only dipole. No tuner needed for either end of the band. A 20 watt BITX CW signal could be a lot more successful than my MFJ-9240 CW transceiver which is about 6-7 watts, and works great for QRP. ??

I am sure a narrow audio filter switched in, would be helpful for focusing on a signal. But how do you put a signal smack on the tuned frequency without rebuilding the whole thing?

On a side note, I used my tablet to generate a 1khz tone, and held the mic to the tablet speaker to check the SWR while adjusting the antenna tuner. Worked great when I had that other antenna up.

Just a couple of bits plus Allisons suggestions although this applies more to the homebrew variety.

Tips n Mods
--
Rob G4NQX

That's a broadband transformer. ?Either core should work fine, and they likely use what they got.

Moving from the Schottky Bat54s back to the two non-schottky 1n4148's would require more drive, not less. ? Near as I can tell, those Bat54s diodes were a problem for W5KUB and for nobody else. ?Allison is referring to the diode ring mixer at D10,11,12,13, and I'm pretty sure is mostly concerned about receiving.

In post?/g/BITX20/message/22042? I gave my rather uninformed take on proper local oscillator injection level into that diode ring, suggesting 7dbm was appropriate for the 1n4148's. ?I can easily believe that 7dbm is appropriate for schottky diodes like the Bat54 but that the 1n4148's require significantly more drive. ?I have no idea how much drive they are currently getting, or how much they should get. ?If the 1n4148's are not getting driven hard enough, might be worth trying a couple Bat54s in that diode ring. ?Properly driven, the 1n4148's might give a larger dynamic range, though most of us wouldn't notice.

Allison mentions impedance matching at the diode ring as also being important, especially where the diode ring sends a signal into that IF amp at Q2 on receive. ?If Q2 presents 200 ohms to the mixer, then the amp at Q1 will see that same 200 ohms when driving the mixer. ?Allison suggests the mixer would perform better in a 50 ohm environment. ?Then higher drive from the local oscillator into the diode ring becomes more important, those diodes will need sufficient current to get them into a lower impedance part of their IR curve. ?Not obvious to me we care about matching impedances into the local oscillator port, I'd think the Si5351 3v pk-pk square wave through a series resistor and dc blocking cap might be sufficient.

Jerry, KE7ER

?

开云体育

Arv's post says to use a T37-6, but both of mine came with T30-6 cores as seen in the picture. The core on the left is a T37-6 and the core on the right is the one shipped with my BitX40 board.

Joel?

KB6QVI

开云体育

Check out Arv's post: ? /g/BITX20/message/19167

Hello, I renew my question in another thread about what the core is the transformer T4.

Unfortunately, my BITX40 came damaged T4 was lying horizontally and detached 2 wires, I suspect damage to the core .... I thought it was the core is FT37-43 but this, however, is different .... I can not find anywhere what is the type of core..

best regards

Tom

Thanks for posting Allison's info over here Jack. Based on this info and the other thread on this message board I tried the 19MHz VFO approach yesterday. I can report that it was very effective.?For reference, my?Bitx is scratch built with termination insensitive amps but overall it follows the latest Bitx40 architecture. I am using the Adafruit SI5351 board to generate VFO and BFO signals.

The rig has been a blast to operate?and the only non-ideal behavior?occured in the evening as?I was hearing CW and SW broadcasts in the phone band. It wasn't terrible, just enough to be a little annoying. The biggest offender was a?station in SC on 7.385 and a quick check of the numbers pointed to the 4th harmonic problem.

When I changed the VFO to 19MHz and moved the BFO to the other side of my IF filter I initially had poor carrier supression and a hollow sounding receiver. Adjusting the BFO down a little more took care of both problems?as expected. Last night I did not hear any SW stations in band that weren't also heard on my reference Kenwood. The big station from SC was booming in on 7.385 but not heard at all in our 40M band. I'm hopeful that the problem is solved. A few more nights of listening?should prove or disprove that.

I did not have the 7200 birdie with my VFO at 4.8MHz but I do have it now. That doesn't bother me though as I kind of avoid that frequency anyway.

So, what does this mean to the rest of us?

"The mixers using 1N914/4148 diodes are not level 7 mixers (nominal 7dbm drive) like commercial DBMs.
the reason for this is Schottky diodes have a lower turn on threshold than silicon junction diodes with the difference being .2V compared to .65V. This means you need more LO drive for the terminal impedance
of all ports to be 50 ohms. It also means they are higher level mixers by about 3db. So enough drive is important to intermod and overload." - Allison

Is this the part where Tom W5KUB "solved" the low TX power problem with taking the SMD dual diode off and replaced it with two regular diodes? It did seem to make a small difference. But not with the 1N60. Only after changing it again with 1N4148.

Is this what she is talking about here? I am not an engineer. So, is it saying lower turn on threshold helps driving the PA? Or is it higher?