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What I am using with bitxs



Raj

Subgroups can only be created by the group's owner

The 4SQRP Club groups.io has well organized and intuitive sub-groups. ? ?It is practicle and works very well. ? ?A subgroup for each of the different BitxXX radios might be appropriate. ? If are a member of the main Bitx20 group then you only have to opt in the subgroup. ?No questions, no waiting. ? One click and you are in. ? ??

?I have a Bitx40 and all the recent posts for the uBitx are not always easy to filter. ? ?Filtering Bitx20 and Bitx20A is a bit of a task as well.

If you can find one at a reasonable price a remote ATU would be my first choice. That would be the most efficient place for the tuner to be.

In my case I use the MFJ-939 auto tuner. The main reason is it works independently of any transceiver manufacturer's tuner interface cable and only requires a few watts for the auto-tune to work. I accept the tradeoff of some additional power to the antenna lost through the mismatched coax cable run.

There is another auto-tuner I saw somewhere that only requires about a watt to tune. However, I chose the MFJ because it has a wider match range (that would be valuable in portable use where I'm hooking a long-wire directly to the tuner, and I don't mind being part of the counterpoise), and because it had a high enough power rating that I could use it on other than QRP rigs.

For QRP, there are some really inexpensive manual tuners. Those could be good, too.

Tom, wb6b

Am 30.08.2018 um 02:37 schrieb escalantea@...:

I tried the suggestion someone mentioned (changing 10K for 8.2K) with same result (no change).
Then I found this diagram, as you can see, the Key? and Paddle have separate plugs and wiring, I will try this next...
I will let you know if it works.
73's
A

You may connect a 10k lin potentiometer directly to the 4k7 resistor and the other end to GND. If you move slowly from 0k to 10k you should hear dits, dit-dahs and then dah.
(original VU2ESE software). You can measure (between GND and blue wire) at which voltage betweeen 4k7 and 10k the dits and dahs will occur and you may calculate the needed resistors. I did so and found 8k2 working for me.
A continuous tone for the straight key will not occur in VU2ESE 4.3 software. There is a menu point "Straight key" which must be activated before. (despite that a straight key could be recognized without any menu change at the analog port A6). If the 10k pot wont bring out dahs try a higher value.

73 Matthias, DD7NT

I don't know what the regulations are in France, but some folks in the UK have indicated there is no hard harmonic level specification in the UK.?

If that is the case in France, I think you could make a case for the uBITX emissions being reasonable because it is a low power rig to begin with. Just don't hook the uBITX up to another amplifier. And probably you would not want to do some of the various TX increase power mods, unless you can be sure the mod doesn't rase the power while destroying the linearity of the TX chain.

Even here in the US many people might use the same sense of pragmatism. As there are some reports of radios that do indeed meet spec, I don't want to do a bunch of mods unless, one, I can actually verify that they are needed and, two, I can actually verify they fixed anything.?

I live in the US so I'm currently working on and plan to verify what levels of harmonics and other undesirable emissions my radio has and fix it accordingly.?

Tom, wb6b

Hi,I? want to add an antenna tuner for my micro bitx. which is the best?? Manual or Auto or Remote ATU? you suggestions and experiences please.
73,VU3JYT,Rajan

Hi Chris,

Did like this and it works.

Arne

The 1157 tail light bulbs are very common, has an 8W and a 25W filament:
? ?

A good quick test of the IRF510's is to check to see if they are still each pulling
something around 100ma of quiescent current when transmitting with no mike audio.

Yep. I did not look closely enough at my own data when u wrote that. 17, 15, and 12-10 each require their own BPF for compliance.?

WA8TOD

Warren,

You said:? ?"They, however, do nothing to suppress the “45MHz - Carrier” spurs on 20 Meters and above.".
The “45MHz - Carrier” spur on 20m is? 45-14=31mhz
The “45MHz - Carrier” spur on 17m is? 45-18=27mhz
Both should be taken out by the transmit LPF's.

There may well be other spurs.
But I was responding to your statement above.

Jerry

Jerry, take a look at the 4th slide in my post. 17 meter SSB has illegal spurs below and above the carrier. I did not mark them but they are at least 10 MHz above and below. They will require a single band BPF just for 17.?

WA8TOD

There's no trouble with that? ?45mhz-Carrier spur until you get to 15 meters and above on SSB.
Down on 20 meters, the spur is? at? 45mhz-14mhz = 31mhz and should be taken out
by the 20m LPF.

When operating CW, this spur is not a factor.

The strength of the spur will depend on how? loud you yell into the mike? (and thus overdrive the mixers).
I believe it is typically 30dB down or so.

Jerry

On Wed, Aug 29, 2018 at 05:43 PM, Kees T wrote:

Anyone tried to reduce the drive at Q20 and Q40 ? to keep from overdriving the poor ol' 12MHz and 45MHz filters in Tx mode. I think Allison suggested replacing R43 and maybe R23 with a 1N4007 diode (only 1N400x diode which has an extra layer and
mimics a PIN diode).?

Its not an issue of over driving the filter its over driving the mixers!? They are easily driven to excess
levels with the available gain.? The hack using the diodes as a gain reducer is if one wanted ALC.
The diodes would provide a control point.

The bigger issue is both amps add up to more than 32DB to as much as 37db( with really good
3904s) of gain roughly translated means with max modulator output the last mixer is being
hammered about 12db harder than it can stand.? It also means due to ground loops the IFs
will pick up RF out of band especially the 45mhz and add it to the mix.? The Bidirectional
amps TX path both need to be cranked down to about 10-11db each.? ?

The goal with the mixers is to keep the input at least 10db below the LO for minimum
distortion and products.. That means with -10dbm in you get about -17dbm out for
LO of at least 5DBm.?

Modulator out put -17dbm... crystal filter -4db.... 21dbm into the 12mhz if (gain of 18db)
netting - -3dbm into the 12 to 45mhz mixer or 7 db over driven.? So we back off the mix 7db
to adjust it but carrier leakage doesn't go down.? IF the IF gain was 11DB the input to the mixer
would be exactly -10dbm as we should.....

Now the 12-45mhz mixer has been happy we go into the crystal filter at -17dbm and it has
about 4db loss so we are back down to -12dbm out of the mixer and filter.? The 45mhz amp
runs about 13db to 16db as 3904s are kinda weak at 45mhz.? However we only need
11db to drive the next mixer and we have more so we over drive it and get crud out.
Likely the cleaner radios have really weak 3904s delivering lower gain.

Simply put once again there is way too much IF gain in the transmit path.? The result
is performance degradation as no good comes from over drive.

The yabut...? when you do that, you then really see how the power amp gain falls
off above 10mhz.

That is the story.? Its not what I'd like to see or wishful thinking.? For transmit?
you do not need much IF gain as the balanced modulator generally has a lot
of output and most crystal filters do not have a lot of loss.? Add to that most
mixers are not tolerant of overdrive they rebel by putting the excess power
into producing even more spurs.

Allison

Have you reduced the gain levels of the drivers to the 12MHz and 45MHz filter in Tx mode to reduce the mixer input levels and seen the effect on the spurs ?

Looks like the 3 mixer clock inputs from the Raduino are set up with a 50 ohm to 50 ohm, 6dB attenuation pad.

73 Kees K5BCQ

Reach is a function of antenna, and the weirdness of the heavens, etc. etc. etc.? All of 10w.? And so many of you have gone really far. I am but a grasshopper.

But it might be fun to get other distance records?? I was pleasantly surprised to see this.

IF the resistors got hot they had to see a lot of RF power like the IRG510 oscillating.

to test them I use a light bulb (12V up to 1A) and drive the gate with? 0 to 5V
At 5V the light should be full on.? IF the gate is grounded to source and the lamp
lights check to see if there is a Source to drain short.

Allison

Likely has RX and no or very low TX.

Allison

Jim,

what the screen trying to say?? Save us squinting at them. ;)

That and feeding at L4 put the? 33-34mhz LPF in the picture and it can be a bit lumpy.
If you want to see the bare amp then after L1 and you have to break the connection.
Cutting the trace is easy as a wire jumper is the fix.

Allison