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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

The gain control on the bias tee is a passive one, so it's probably best to set that for minimum attenuation and maximum signal levels anyway.

Then adjust the gain control on the loop amplifier board.

There is no point adding more gain than necessary in the loop amplifier, only to counteract it by applying attenuation later in the signal chain.

Ideally, you should aim for approximately 6dB increase in the KiWi noise floor at frequencies around 20 to 30MHz, when the antenna is powered.

Any more than this, and you will not improve the Signal To Noise Ratio, but you will be eating away at the receiver's dynamic range, and making it more prone to overload on strong signals.

A 6dB increase in noise floor, when the antenna is connected, is the "sweet spot" to aim for.

Regards,

Martin

This is a typical data sheet for the type of ceramic patch used in the small GPS puck.

https://datasheets.kyocera-avx.com/ethertronics/AVX-E_1001039.pdf

Note the 70x70mm PCB ground plane used in the measurement test setup.

The 30x30 PCB inside the puck is really just a bit too small, and the polar diagram and off-axis noise rejection is improved by having a larger ground plane below it.

Many of the external GPS antennas are basically just the guts of a puck, mounted on a larger ground plane, and inclosed in a waterproof housing.

Regards,

Martin

I watched one of Techmind's video's relating to the End feed antenna.

https://youtu.be/VYt3-jkBfaQ?feature=shared

Some things of note.

He is on the edge of rural farmland, so the noise floor will be lower than if he was in the middle of at typical UK housing estate, it is also likely that his utility services will be buried rather than being carried by overhead wires, which will further improve the noise floor.

He has installed the antenna in the best way possible, with the feed point located way from the property, and he has also installed a choking balun and separate RF ground, although this could be further improved. Ideally, he should also have incorporated some form of galvanic isolation, in order to reduce the risk of ground loops, or possible issues with UK wiring regulations and mains safety.

Regards,

Martin

I wouldn't trust a Chinese made torque wrench.

It's unlikely that the KiWi will be repeatedly connected and disconnected as much as some other equipment.

Slightly past hand tight is fine, and don't use a big adjustable wrench.

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

To be honest, I'm not surprised.

Many European based short wave broadcasters in the 31m / 9MHz band are massive signals during early evening / night time here in the UK, and we are not even in the target service area.

I have to reduce their level by 20dB using an external notch filter, otherwise the KiWi complains quite badly.

The Voice or Turkey on 9460kHz is particularly problematic, as it targets Europe.

If you want a further challenge, try using the HFDL extension on different frequencies, to receive aircraft and ground stations, these will give you a better idea of what your Kiwi and loop are actually capable of.

Regards,

Martin