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Hi All,

What is the consensus for a SMT replacement for the 2n3904?

I note the MMBT10 only has Vceo of 25 vs 40 for the 2n3n04.

I really do not want to tack leaded parts onto the board.

My latest ubitx is only getting 2w out on 15m, and i want to improve
the 45 Mhz transistors, and the tx drivers.

Rod KM6SN

I made the attached files for my own reference during work on my uBitx which I have now suspended. But I thought they might be helpful for those still engaged in trying to filter the radio with external LPF/BPF combinations. This was my uBitx with the filters completely removed so I could see what parameters would be needed for an external filter to work satisfactorily. There are four slides included. Here are my comments on each:

80,40,20 meter CW
- Power level set on each band individually to 5 watts
- Green display line represents the -43 dBc threshold
- Second harmonic on both 80 and 40 is somewhat problematic as are odd harmonics out to 13th

80,40,20 meter SSB
- Power level set on each band individually to 5 watts CW then 1 kHz tone input level adjusted to produce the same 5 watts
- Green display line represents the -43 dBc threshold
- Second harmonic on both 80 and 40 is somewhat problematic as are odd harmonics out to 9th

17, 15, 10 meter CW
- Power level set on each band individually to 2 watts
- Green display line represents the -43 dBc threshold
- Harmonics can all be removed with a simple 34 MHz LPF. The filter included in the uBitx is more than adequate

17, 15, 10 meter SSB
- Power level set on each band individually to 2 watts CW then 1 kHz tone input level adjusted to produce the same 2 watts
- Green display line represents the -43 dBc threshold
- 17 meter spurs represented by markers 1 and 2 are problematic because only a close spaced, single band BPF can be used to remove them.
- 15 meter spurs at the low end need to be addressed.
- A single filter cannot cover these bands because of the close spaced 17 meter spurs.
WA8TOD

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Ajay,

This was addressed in this thread but I probably don't blame you if you don't want to read through several hundred posts and comments to find it.

The EFHW antenna with the 49:1 transformer works reasonably well on any band where the wire itself is resonant. That is not due to the resonance so much as to the very high impedance presented by a resonant half wave and the consequent good match to the 49:1 transformer. The reason the MyAntennas antenna MAY ( I have not tested it but I understand what they have done) is the wire is supplied with a six turn coil that effectively lengthens the antenna on higher, harmonically related bands. I suspect therefore it presents a resonant load on 80, 40, 20, and 10 meters. On bands where the wire/coil combination is not resonant, 60, 30, 17, and 12 meters, the system will show a deceptively low VSWR due to losses in the now mismatched transformer. The antenna will perform but as much as 90% of your output power will be converted to heat on these bands rather than radiating.

The homebrew antenna/wire does not use the carefully engineered coil and is therefore resonant on only one band, if even that. So this antenna, as recommended on the FB group, completely relies upon losses in the transformer to produce artificially low VSWR while converting the majority of your power into heat. If the wire is carefully cut to half wave resonance on any one band the system will show reasonable losses. It will not work well on harmonically related bands because of the shortening effect of multiple half waves in series which moves the frequency of resonant harmonics higher than the normal integer multiples.

In both cases, the MyAntenna wire and the homebrew wire, a simple LC tuner represents a better solution than the transformer. Typical losses using a tuner are normally well under 1 dB or less than 5%. Typical losses using a 49:1 transformer with a resonant wire are 1-2 dB (10 - 20%). Typical losses using a 49:1 transformer on bands where the wire is not resonant can easily be 10 dB or 90%.

In all cases a tuner represents the best performance.?

WA8TOD

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Yeah, a mag loop will do a great job of attenuating not only the spurs or harmonics into oblivion----and almost that destination for your desired signal as well!!? ?I've seen efficiency figures of -10 dB.? ?

?

Hoping that's not true foryou.....

Gordon

Good job W4OP!

Indeed I think the threads here have been much more informative than the Facebook group and those magic videos.

Mike

I don't think this is IMD per se. It looks to me like harmonics of the modulating tone. Those harmonics could be present in the tone itself or they could be generated by non-linearities in the audio chain.

For IMD measurements you need two tones with the pair centered in your filter passband and the tones must not be harmonically related. The difference between one of the tones and its adjacent product tone is the figure of merit for IMD. Your span and RBW are ok although if you have a lower RBW, 30 or 10 Hz, you will get better resolution and may see some close in products that are covered up at 100 Hz.

W