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Hi

This morning I had an hour to spare so I switched on the μbitx and there was good propagation on 18 MHz.
So I switched on the Drake R8 to compare the signals.

The R8 agc was set to off as the μbitx does not have agc, preamp off as the μbitx does not have an RF amplifier, and the bandwidth set to 2.3 kHz.

I swapped the antenna between the two sets several times and made a video which I uploaded on youtube.

In the video you may notice some difference on the digital readputs because I had initially not set the two sets on exactly the same frequency during the video , but later on I set both on the same frequency and they both tallied 100%.

As regards sensitivity both appeared to be approximately the same with the R8 having a slight edge on the μbitx and obviously greater audio output of the R8 which was set at approximately half way while the μbitx volume was full on.

Those wanting more audio could get one of the cheap available amplifiers such as

1x 2x18W TDA2030A 2.0 Double Track TDA2030A Audio Amplifier Board Module X4Z5 US $5.27

PAM8403 2 Channel USB Power Audio Amplifier Module Board 3Wx2 Volume Control US$1.59

5pcs PAM8403 Miniature Digital USB Power Amplifier Board 2.5V - 5V US$2.67

15W TDA7297 Dual-Channel Amplifier Board For Arduino US$3.92 US$1.63 via Air Parcel Registe

3Pcs TDA2030 TDA2030A Audio Amplifier Module US$3.70 US$1.59 via Air Parcel Register

Enjoy

Regards?

Lawrence

#64313

Lawrence

Good data!? Please notice that sensitivity relates to our ability to copy a signal in the background (and rig supplied) noise -- not how much audio the receiver can pump into the air.? yes I perceive you already agree.?

how a receiver changes with preamp on and off does vary with how gain is built into the receiver.? a receiver can be 'gain limited' - meaning more gain would improve sensitivity or 'noise limited' - which you can guess means more gain does not improve sensitivity.?

depending upon our latitude, season etc. the background noise does vary.? at lower HF there is more noise in the atmosphere than our receivers can make, this only changes at the upper part of the spectrum.? in a quiet area with little man-made noise it will be interesting to compare the uBITX to receivers having a preamp on 28 MHz.? I am expecting only a small difference, less than one S-unit maybe.

likely many already know this, but QRN is propagated via the ionosphere - often from tropical regions.? cool stuff!

73 Curt

#64322

Agree.

That's why I set the R8 without a preamp like the μbitx.

Re more audio on the R8 it was to explain on the different audio levels between the two receivers and a hint for those who would like more audio but with headphones should be ok on marginal signals.
As you said noise is the limiting factor on the lower frequencies and adding an amplifier will not only boost the signal but also the background noise.
However, it may, in relatively quiet locations, give a better copy as it may override the receiver internally generated noise and other losses within the receiver.
it would be interesting if someone who may have changed the receiver first 45 MHz IF section with hotter / lower noise transistors to report on the result.

Regards

Lawrence

Show quoted text

On Fri, Jan 25, 2019 at 12:24 AM Curt via Groups.Io <wb8yyy=[email protected]> wrote:

Lawrence

Good data!? Please notice that sensitivity relates to our ability to copy a signal in the background (and rig supplied) noise -- not how much audio the receiver can pump into the air.? yes I perceive you already agree.?

how a receiver changes with preamp on and off does vary with how gain is built into the receiver.? a receiver can be 'gain limited' - meaning more gain would improve sensitivity or 'noise limited' - which you can guess means more gain does not improve sensitivity.?

depending upon our latitude, season etc. the background noise does vary.? at lower HF there is more noise in the atmosphere than our receivers can make, this only changes at the upper part of the spectrum.? in a quiet area with little man-made noise it will be interesting to compare the uBITX to receivers having a preamp on 28 MHz.? I am expecting only a small difference, less than one S-unit maybe.

likely many already know this, but QRN is propagated via the ionosphere - often from tropical regions.? cool stuff!

73 Curt

#64324

Exactly it is sensitive enough as tabletops or portables (degen 1103, Sangean 909 etc). The difference may be in other characteristics, like blocking, the presence of BPF, signal handling, but as for sensitivity it is very hard to find a real deaf one if everything is functioning well.

Show quoted text

Il 25/gen/2019 09:12, "Lawrence Galea" <9h1avlaw@...> ha scritto:

Agree.
That's why I set the R8 without a preamp like the μbitx.
Re more audio on the R8 it was to explain on the different audio levels between the two receivers and a hint for those who would like more audio but with headphones should be ok on marginal signals.
As you said noise is the limiting factor on the lower frequencies and adding an amplifier will not only boost the signal but also the background noise.
However, it may, in relatively quiet locations, give a better copy as it may override the receiver internally generated noise and other losses within the receiver.
it would be interesting if someone who may have changed the receiver first 45 MHz IF section with hotter / lower noise transistors to report on the result.
Regards
Lawrence

On Fri, Jan 25, 2019 at 12:24 AM Curt via Groups.Io <wb8yyy=[email protected]> wrote:
Lawrence

Good data!? Please notice that sensitivity relates to our ability to copy a signal in the background (and rig supplied) noise -- not how much audio the receiver can pump into the air.? yes I perceive you already agree.?

how a receiver changes with preamp on and off does vary with how gain is built into the receiver.? a receiver can be 'gain limited' - meaning more gain would improve sensitivity or 'noise limited' - which you can guess means more gain does not improve sensitivity.?

depending upon our latitude, season etc. the background noise does vary.? at lower HF there is more noise in the atmosphere than our receivers can make, this only changes at the upper part of the spectrum.? in a quiet area with little man-made noise it will be interesting to compare the uBITX to receivers having a preamp on 28 MHz.? I am expecting only a small difference, less than one S-unit maybe.

likely many already know this, but QRN is propagated via the ionosphere - often from tropical regions.? cool stuff!

73 Curt

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