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Hello all,

A couple of questions to bounce off all -- since the IF is 12Mhz (maybe change to 10.7 to get it further from 20m), couldn't 20-10 meters use the mixer sum, instead of difference, and this would automatically switch the sideband to upper? ?Also, would it simplify the filtering to use a robust bandpass filter for each band for both T and R, eliminating the need for a separate LPF?

Thanks

Burton Ison

W5IAC

Hi again. I searched the site but couldn't find an answer to my new problem. The radio has been working just fine for awhile now. However after trying a few qso's with strong stations, I realized that I have no transmit audio. I suspected a bad wire from the electret mic to the board, but that doesn't seem to be it. I don't know how to test the mic element, as I only have a DMM and no scope. So far I have measured PA current and have the 100ma, however when I do the hallloooww thing, I get no increase in current. I also monitored my signal on my base hf rig and get no S meter fluxuation as I yell into the mic. I'm in the process of printing out the mic input circuit so I can start taking voltage and resistance readings. Any suggestions are always appreciated. WA1MAD

It looks like women who make BITX40 instead of L1. L2, L3 bandpass filter solder coils used in VFO ..... after reducing 10 turns of each coil L1, L2, L3 my BITX40 works in RX and TX as it should .... anyway I'm waiting for uBITX ....: )

Tom

Good Afternoon,

So just got my Bitx40 up and running, made a few contacts with just a dipole. But even with my commercial rig some contact have told me i have a light voice. So is there any way i could add some mic gain. (Sorry if this is a noob question). Also what types of meters are you guys using to measure your output. I had a cross needle? hooked up but showed little to no RF power out.

73

KE8CPD

Sure. ?In theory you could crack open the IRF510 package and cool the die with liquid nitrogen. ?In practice, much easier to go with multiple devices. ? I suggest you copy the push-pull IRF510 amp plus the 3 driver stages that Ashhar has on the uBitx, and run that at 24v: ?

Primary issue is heat dissipation. ?The IRF510 is spec'd at 3.5 degrees C from die to the TO220 tab. ?Assuming 50% efficiency, ,at 36 watts the die is dissipating 36 watts as heat. ?So the die is 36*3.5 = 126 degrees C ?or 227 degrees F hotter than the tab. ?And the tab is going to be hotter than your heatsink. ?And the heatsink is hotter than the ambient air. ?From that, it's clear that asking 25 watts per IRF510 is already asking a lot. ?If your IRF510 heatsink is anything more than lukewarm, then the die is close to molten.

Jerry, KE7ER?

I have been reading stuff here about low power or audio for about 3 months now because my BITX40 was factory set to low power (drawing .024 mA at the final during wireup), output and also sounded like the audio should be louder. ?R136 was a mystery to everyone but me when I discovered it adjusts the PA current draw and power output. It seems to have been deleted or left out from the alignment steps at the bottom of the wire up page. Look at #5, it's blank. This is still tripping up noobs who just got one today, i'm sure.

There have been some people talking about "speech compressors". And I think it's time I try it. I never heard of it before. And some of what I have seen here including PDF's Seems to assume I already know how to pick it up and use it. I can make circuitry just fine. But it's how to make the two work together, mostly because speech compressors are totally new to me, that's holding me back from starting such a project.

Could some of you fine folks point me and probably some others of the gang, towards some basic info to bring me up to speed on using speech compression, and why I need it? And speech compressors with the BITX40 board? Some links would probably save you a bunch of writing time. But personal perspectives would be greatly appreciated too.?

Thanks in advance.

To which power connector does one apply 24 volts if one wants to try to boost power?

I use two sets of Anderson power poles.?
I can run the whole thing on 1 gel battery or 2 gel batteries.
I have a switch wired such that the two batteries are
a) in parallel, or
b) battery #2 is 'stacked' on top of battery #1

"b" allows one battery to run the transceiver's 'main' power, and the top of the 'stacked pair' (~25V) to run the PA.
With 25V, I get from 20 to 24 Watts. PA gets HOT HOT HOT, so... heatsink away.

Mike Yancey, KM5Z
Dallas, Texas

Remove C91, C92 from the Bitx40 if you have not already, they bleed away too much of the VFO energy when the VFO is much over the stock frequency of 5mz. ?Those caps are only required if using the analog VFO.

Ok I have got the 40/80 M working and USB and LSB at least on 40m USB 3khz low approx. ?When I try to get to anything above 40m my receive gets lower and lower Probably LPF other than the Bandpass 40M Filter I put a switch on and open BPF and still Low RX, and low TX as well. ?Is there a LPF that I am missing somewhere or what mods can I do to get to as high as 20M. ?Is there any sketches written? Software or Hardware any help links would be great.