Month: March 2021

Comment on KN5L on balun CMRR – two wire line example

The article Comment on KN5L on balun CMRR dealt with model and measurement of John’s coaxial choke in fixture, dealt with first because it is a simpler model. This article builds on that and models the balun wound with a pair of wires.

Above is the subject balun in fixture.

John’s schematic shows the balun as coupled coils, but that does not capture the transmission line transformation that occurs in the actual device. Again the test fixture is used without explanation. Continue reading Comment on KN5L on balun CMRR – two wire line example

Last update: 1st April, 2021, 6:46 AM

Comment on KN5L on balun CMRR – coax example

One of the ham fashions of proposed solutions to characterising a balun is to find the Common Mode Rejection Ratio (a term carried over from other applications, eg voltage driven operational amplifiers).

(Anaren 2005) explains a method of finding balun CMRR. Anaren gives a definition of CMRR:

Common Mode Rejection Ratio is defined and the ratio between the differential mode insertion loss/gain versus the common mode signal loss or gain.

Note that in a passive system, CMRR (or CMR) in dB will usually be positive, and the larger the better. You might even think that the plain English meaning of the words Common Mode Rejection Ratio would suggest that a large ratio (or high +ve dB value) would mean most rejection, goodness. Such a meaning would be quite consistent with that of CMRR (CMR) applied to operation amplifiers (for a very long time).

Anaren does not mention applying the CMRR statistic to antenna systems. I have commented elsewhere on the lack of utility of CMRR in analysing common antenna systems.

Then immediately after the above definition, they give a formula which implies the inverse:

\(CMRR=\frac{S_{1c}}{S_{1d}}\) and goodness would be a tiny fractional value, or a small (-ve) dB value.

John, KN5L, has published his own solution to balun characterisation in some online forums. Continue reading Comment on KN5L on balun CMRR – coax example

Last update: 13th May, 2024, 10:10 AM

Baofeng BF-T1 (BF-9100) – initial impressions

I purchased two inexpensive Baofeng BF-T1 UHF portables (hand-helds) for use around the yard.

Key features:

  • LiIon pouch single cell battery that may be obtainable longer than proprietary batteries;
  • micro USB charger interface, internal charge / battery management;
  • programmable with CHIRP (channel table only);
  • chanellised operation, lockable keypad;
  • CTCSS support;
  • integrated antenna;
  • small and lightweight (110g with belt clip);
  • inexpensive.

The radio has been in the market for more than three years, so one might hope that design issues have been fixed in ‘mature’ product. Continue reading Baofeng BF-T1 (BF-9100) – initial impressions

Last update: 6th April, 2021, 12:44 PM

Comparing sensitivity figures of an AM receiver and SSB receiver

Receiver sensitivity is commonly given as some signal level, say in µV, for a given Signal to Noise ratio (S/N), say 10dB. For AM, the depth of sinusoidal modulation is also given, and it is usually 30%. In fact these are power ratios in the context of and some nominal reference receiver input impedance.

In fact what is commonly measured is Signal + Noise to Noise ratio, and of course this ratio is one of powers. For this reason, specifications often give (S+N)/N.

This article discusses those metrics in the context of ‘conventional’ receivers and introduces the key role of assumed bandwidth through the concept of Equivalent Noise Bandwidth..

Let’s consider the raw S/N ratio of an ideal AM detector and ideal SSB detector.

Raw Signal/Noise

AM

 

Above is a diagram of the various vector components of an AM signal with random noise, shown at the ‘instant’ of a modulation ‘valley’. The black vector represents the carrier (1V), the two blue vectors are counter rotating vectors of each of the sideband components, in this case with modulation depth 30%, and the red vector is 0.095V of random noise rotating on the end of the carrier + sideband components. Continue reading Comparing sensitivity figures of an AM receiver and SSB receiver

Last update: 28th March, 2021, 6:03 AM

Low power Guanella 1:1 balun with low Insertion VSWR using a Fair-rite 2×2631540002 – measurement of Zcm

Low power Guanella 1:1 balun with low Insertion VSWR using a pair of Fair-rite 2631540002 suppression sleeves – design workup presented a desk design of a low power balun. This article presents measurement of common mode impedance Zcm of a prototype using a nanoVNA.

Above is the prototype 2631540002×2 wound with 3.5t of RG316. Continue reading Low power Guanella 1:1 balun with low Insertion VSWR using a Fair-rite 2×2631540002 – measurement of Zcm

Last update: 22nd March, 2021, 5:39 PM

Low power Guanella 1:1 balun with low Insertion VSWR using a Fair-rite 2843009902 binocular – measurement of Zcm

Low power Guanella 1:1 balun with low Insertion VSWR using a Fair-rite 2843009902 binocular – design workup presented a desk design of a low power balun. This article presents measurement of common mode impedance Zcm of a prototype using a nanoVNA.

Above is the prototype 2843009902 binocular wound with 3.5t of RG316. Continue reading Low power Guanella 1:1 balun with low Insertion VSWR using a Fair-rite 2843009902 binocular – measurement of Zcm

Last update: 22nd March, 2021, 8:43 AM

Baofeng BF-F8HP battery and charging experience

The Baofeng BF-F8HP is a U/V portable FM transceiver. The battery supplied is labelled BL-5 and rated at 2800mAh.

Of course it is supplied with a Chinese power supply that does not comply with Australian Standards, and is illegal to sell in Australia, even second hand by a non-business seller.

It seems common that Baofeng portables use a charger cradle that is powered from nominally 10VDC. The question arises as to the maximum input voltage. Continue reading Baofeng BF-F8HP battery and charging experience

Last update: 21st March, 2021, 10:58 AM

Baofeng GT-5TP battery and charging experience

The Baofeng GT-5TP appears to be a UV-82 derivative… there are many such derivatives. The battery supplied is labelled BL-8 and rated at 2000mAh. It seems that Baofeng makes two incompatible batteries labelled BL-8, a slightly different (but incompatible) BL-8 battery is used on the UV-82.

Of course it is supplied with a Chinese power supply that does not comply with Australian Standards, and is illegal to sell in Australia, even second hand by an end user.

It seems common that Baofeng portables use a charger cradle that is powered from nominally 10VDC. The question arises as to the maximum input voltage. Continue reading Baofeng GT-5TP battery and charging experience

Last update: 20th March, 2021, 9:27 AM

Low power Guanella 1:1 balun with low Insertion VSWR using a Fair-rite 2843009902 binocular – design workup

The article Low power Guanella 1:1 balun with low Insertion VSWR using a pair of Jaycar LF1260 suppression sleeves describes a current balun with low Insertion VSWR for operation at modest power levels. The design was based on Jaycar LF1260 cores which are readily available in Australia.

This article presents the workup of a balun with similar design objectives using a low cost Fair-rite 2843009902 binocular core (BN43-7051).

Above, a pic of the core. Continue reading Low power Guanella 1:1 balun with low Insertion VSWR using a Fair-rite 2843009902 binocular – design workup

Last update: 8th January, 2022, 6:12 AM

Review of MXITA SMA-8 #2

The MXITA SMA-8 is a low cost torque wrench for 8mm, specifically for SMA connectors. It has an adjustable calibration, supplied at 1Nm but easily adjusted down to 0.6Nm to suit common brass SMA connectors, especially of doubtful quality.

I bought this after seeing several recommendations on a nanoVNA forum.

Above is the factory pic of the SMA-8. Continue reading Review of MXITA SMA-8 #2

Last update: 19th March, 2021, 6:29 PM