G8JNJ

A question for the signal theory experts (Preamplifier gain)

G8JNJ

September 2019

>
>broadband magnetic loop, digital mode, there was no obvious advantage beyond about 3db (lowest) increase in noise floor
>

That's highly likely.

Glenn was spot on with his previous statement.

>… (more)
> It is more difficult to approach propagated and galactic noise floors with a small antenna, whether loop or dipole. It may not even be possible at mid-upper HF given typical >site signal levels and available active devices
>

With your loops and LZ1AQ amplifier, I suspect that the antenna performance is likely to be about 10dB worse than the sensitivity required to hear the galactic noise floor on the upper HF bands, so as soon as you see the noise from the amplifier raising the KiWi noise floor, you won't really notice any further improvement.

Very few (if any) 1m diameter active loops are capable of hearing down to the galactic noise floor on these frequencies, so it's not that you are doing anything wrong, it's just the laws of physics constraining things. There have been many previous threads on this subject if you wish to trawl back through them.

This is one of my gripes about Youtube videos where folks compare different receivers, but are using something like a Wellbrook loop as the antenna. In most cases the antenna is the limiting factor and not the actual receiver. In fact I despair about the trend with amateur transceivers where folks seem to gravitate towards equipment with very large dynamic range figures, whereas in all likelihood they will never be able to take advantage of it, because they are using compromise antennas in noisy urban environments. If you take a look at a lot of the KiWi's that are on line, many of them are struggling to achieve 20 or 30 dB dynamic range (max signal level to noise floor) for these reasons, so having a receiver capable of >120dB dynamic range is pointless.

I got close to achieving maximum sensitivity by using a combination of my TC2M broadband vertical, followed by a DXE-RPA1 copy 13dB low noise pre-amp and then a passive amplitude slope equaliser and selective BC band notches. By doing this I could have much greater RF gain on the HF bands, but roll it off on the LF bands where the natural noise floor was already higher than the KiWi baseline noise figure of somewhere around 14dB. However even this was not good enough to hear emissions from Jupiter at around 20MHz, which is what I was hoping for.

Regards,

Martin - G8JNJ (less)

A question for the signal theory experts (Preamplifier gain)

G8JNJ

September 2019

>
>broadband magnetic loop, digital mode, there was no obvious advantage beyond about 3db (lowest) increase in noise floor
>

That's highly likely.

Glenn was spot on with his previous statement.

>… (more)
> It is more difficult to approach propagated and galactic noise floors with a small antenna, whether loop or dipole. It may not even be possible at mid-upper HF given typical >site signal levels and available active devices
>

With your loops and LZ1AQ amplifier, I suspect that the antenna performance is likely to be about 10dB worse than the sensitivity required to hear the galactic noise floor on the upper HF bands, so as soon as you see the noise from the amplifier raising the KiWi noise floor, you won't really notice any further improvement.

Very few (if any) 1m diameter active loops are capable of hearing down to the galactic noise floor on these frequencies, so it's not that you are doing anything wrong, it's just the laws of physics constraining things. There have been many previous threads on this subject if you wish to trawl back through them.

This is one of my gripes about Youtube videos where folks compare different receivers, but are using something like a Wellbrook loop as the antenna. In most cases the antenna is the limiting factor and not the actual receiver. In fact I despair about the trend with amateur transceivers where folks seem to gravitate towards equipment with very large dynamic range figures, whereas in all likelihood they will never be able to take advantage of it, because they are using compromise antennas in noisy urban environments. If you take a look at a lot of the KiWi's that are on line, many of them are struggling to achieve 20 or 30 dB dynamic range (max signal level to noise floor) for these reasons, so having a receiver capable of >120dB dynamic range is pointless.

I got close to achieving maximum sensitivity by using a combination of my TC2M broadband vertical, followed by a DXE-RPA1 copy 13dB low noise pre-amp and then a passive amplitude slope equaliser and selective BC band notches. By doing this I could have much greater RF gain on the HF bands, but roll it off on the LF bands where the natural noise floor was already higher than the KiWi baseline noise figure of somewhere around 14dB. However even this was not good enough to hear emissions from Jupiter at around 20MHz, which is what I was hoping for.

Regards,

Martin - G8JNJ (less)

Need to attenuate LW 252 Khz

G8JNJ

August 2019

Hi Mark,

Here's a simple notch that should do the trick and give you a 20dB deep notch on 252KHz.

It's just a series tuned circuit wired across the antenna feed into the KiWi.

You may need to fine tune… (more)

Channel Button

G8JNJ

August 2019

Hi Stu,

This is an interesting idea, but it looks a bit cumbersome (if I understand what you are proposing correctly).

I wonder if another method would be to allow users to navigate by 'stepping'… (more)

W/F and SND Bad Params

G8JNJ

August 2019

Hi Glen,

I was able to enter these commands directly via the KiWi admin console page.

I don't know if this is possible, but the responses I got back seem to indicate that it worked OK.

Regards,

Martin - G8JNJ

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G8JNJ

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A question for the signal theory experts (Preamplifier gain)

A question for the signal theory experts (Preamplifier gain)

Need to attenuate LW 252 Khz

Channel Button

W/F and SND Bad Params