Amateur Radio – Page 60

Vacuum capacitors – construction implications for Q

Vacuum capacitors are used for high end applications that require high voltage withstand and low loss.

Though they are called capacitors, and simple analyses treat them as a capacitance with some small equivalent series resistance (ESR), there is more to it.

Above is a view (courtesy of N4MQ) looking into one side of a vacuum capacitor. It consists of an outer cup, and a series of 5 inner cups progressively smaller in diameter. The other side of the capacitor has a similar structure but the cups site in the middle of the spaces between cups in the first side.
Continue reading Vacuum capacitors – construction implications for Q

Last update: 19th January, 2018, 9:38 AM

60dBm.com 0.1-3000MHz Return Loss Bridge

This article is an expose of the internals of a 60dbm.com 0.1-3000MHz Return Loss Bridge available on eBay for around $17 incl post.

Above, the 60dbm.com Return Loss Bridge. Continue reading 60dBm.com 0.1-3000MHz Return Loss Bridge

Last update: 20th November, 2019, 6:31 AM

Baofeng charger DC-DC converter

One of the insane things about some Baofeng hand held radios is that the charger cradle requires 10V DC, and malfunctions on car battery voltage.

The cigarette light adapter that came with a Baofeng GT-3TP was simply a pass through device and the charger did not work properly using the adapter plugged into a car.

The charger cradle electronics should include electronics to charge properly from a car, preferably from 10-16V. The implementation is a half-baked idea.

To solve the problem I have made an adapter cable using a small buck DC-DC converter off eBay (~$2), the converter is adjusted to 10V out.

I have used an Anderson Power Pole connector to suit my power distribution, you could use a cigarette lighter plug or some other plug to suit your needs. The output connector is a 2.5mm DC plug. Continue reading Baofeng charger DC-DC converter

Last update: 17th January, 2018, 12:27 PM

Chinese no-name 1-1000MHz Return Loss Bridge

This article is an expose of the internals of a common Chinese no-name 1-1000MHz Return Loss Bridge available on eBay for around $65 incl post.

Above is the exterior of the device. Specs are sparse: P<23dBm, Directivity>35dB. Continue reading Chinese no-name 1-1000MHz Return Loss Bridge

Last update: 11th January, 2018, 6:00 AM

Do we sound like a bunch of chooks or what?

Though ham radio enthusiasts often rail against CBers, with the eflux of time, it is more difficult to distinguish between the two.

From Innovantennas website, a caption to a pic of one of their antennas explains:

The 10-54MHz LDPA directional antenna at K4ANP. Sadly, Len caught one of the elements and vent it during installation but SWR 1:1.4 thorughout.

The emphasis of the SWR value is mine. They, as antenna ‘professionals’, do not seem to understand the concept of SWR, and that by definition it is a ratio of greater than unity, ie the big number goes first. In fact if they just rationalised the ratio and expressed it as SWR=1.4 it would be briefer, clearer and more importantly, actually correct.

Little wonder hams not really understand what they are buying acquire bad learning from those who might provide accurate information.

Last update: 10th January, 2018, 10:28 AM

Review of inexpensive QRP ATU kit from eBay

This article is a review of an inexpensive QRP ATU kit sold widely on eBay and possibly other online stores.

Above is the seller’s pic of the kit. Continue reading Review of inexpensive QRP ATU kit from eBay

Last update: 21st October, 2020, 4:09 PM

Where do µ’ and µ” come from?

Lets say we measure the impedance of a 1t wind on a FT240 size core to have Z=13.6+j19.1Ω @ 7.31MHz.

But it has a resistive component, it is not an ideal or lossless inductor.

Nevertheless, we can consider that Z=j*2*pi*f*L, and since Z is complex, a complex values is implied for L. Continue reading Where do µ’ and µ” come from?

Last update: 9th January, 2018, 10:29 AM

Baofeng GT-5TP – first impressions

This article documents an initial checkout of a Baofeng GT-5TP.

Above is the GT-5TP with its supplied antenna. Continue reading Baofeng GT-5TP – first impressions

Last update: 19th January, 2018, 10:26 AM

End Fed Half Wave matching transformer – 80-20m

A prototype broadband transformer for a End Fed Half Wave operated at fundamental and first, second, and third harmonic is presented.

The transformer comprises a 32t of 0.65mm enamelled copper winding on a FT240-43 ferrite core, tapped at 4t to be used as an autotransformer to step down a load impedance of around 3300Ω to around 50Ω. The winding layout is unconventional, most articles describing a similar transformer seem to have their root in a single design.
Continue reading End Fed Half Wave matching transformer – 80-20m

Last update: 23rd May, 2022, 2:36 PM

Line loss under standing waves – recommendation of dodgy tool on eHam

In a discussion about using a 40m centre fed half wave dipole on 80m, the matter of feed line loss came up and online expert KM1H offered:

Use this to help make up your mind. Add it to the normal coax loss. http://www.csgnetwork.com/vswrlosscalc.html

This is to suggest that the feed line loss under standing waves can be calculated with that calculator.

He then berates and demeans a participant for commenting on his recommendation, bluster is par for the course in these venues.

Calculator analysis

The calculator in question states this calculator is designed to give the efficiency loss of a given antenna, based on the input of VSWR (voltage standing wave ratio) and other subsequent factors.

This is a bit wishy washy, efficiency loss is not very clear. The usual meaning of efficiency is PowerOut/PowerIn, and the usual meaning of loss is PowerIn/PowerOut, both can be expresssed in dB: LossdB=10*log(Loss) and EfficiencydB=10*log(Efficiency). Continue reading Line loss under standing waves – recommendation of dodgy tool on eHam

Last update: 14th September, 2020, 8:05 PM