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Hi John,

Not a big deal, but it may be related to the mouse behaviour.

I notice that sometimes when I click on the waterfall, the KiWi doesn't tune to that frequency, but it remains on an existing frequency. A second click is then required before it tunes correctly.

I have only noticed this over the past month or so, but it may have been like this for a while.

Regards,

Martin

An End Fed wire antenna is by it's nature not balanced, and they have a reputation as tending to be noise magnets. A wire dipole, loop or active loop are better options.

With your KiWi a lack of signal level seems to be the main issue. Even if there are few signals I would expect to be seeing more noise.

Is the loop antenna (I assume an MLA-30) powered correctly ?

If it is an ML-30 have you experimented with the two gain controls (one in the bias tee, the other in the loop amplifier) ?

Regards,

Martin

Unbalanced antennas are prone to noise pickup on the feed line.

Use a balanced antenna if you can, as this will provide better results.

Concentrate on the Signal to Noise Ratio rather than absolute signal strength.

A good transmit antenna is not necessarily a good receive antenna. Antenna efficiency is important on transmit, but much less so when only used for receive.

Site an antenna for the lowest noise level rather than the strongest signals.

With receive systems, it is the Signal to Noise Ratio that matters. As long as the antenna gain / sensitivity is sufficient to raise the receiver noise floor by 6dB relative to a screened 50 ohm load, then you can't improve the antenna performance any further, other than by increasing the directivity.

Directivity increases the gain in the required direction, but more importantly reduces gain in unwanted directions, including noise sources. If you have much more than 6dB increase in noise floor, you are eating away at your receiver's dynamic range, and this is especially important with wideband receivers such as the KiWi.

Owen Duffy (one of my heroes) introduced the concept of Signal to Noise Degradation, and he has many posts on the subject.

https://owenduffy.net/blog/?p=30632

ITU noise curves and required receiver noise figure. For reference, the KiWi NF is around 14dB, which is adequate at 30MHz.

https://owenduffy.net/blog/?p=15700

As you can see, a very high noise figure receiver is adequate at 1MHz, which is why electrically short active antennas can still work well at such low frequencies.

Regards,

Martin

The GPS puck is designed to mounted on a car, so it has to be siting to a metal surface in order to have an adequate ground plane, and function correctly.

It doesn't need to be anything sophisticated, and something like a biscuit tin, or similar, is fine.

Almost anything will do, but it does help improve the polar diagram and overall sensitivity.

Regards,

Martin

In my linear supplies, I had to swap conventional silicon rectifiers for Schottky types, as the 1.6 voltage drop and 3A + forward current was producing about 5 w of heat.

The downside of Schottky types, is that they have faster switching times, and as a result, they can produce additional RF interference, unless extra R & C snubbing components are added.

Regards,

Martin