09 January 2015

Homebrew Attenuator Measurements contd

It was interesting to measure the insertion loss and maximum attenuator accuracy over a wider frequency range.

The BIG attenuator has a maximum attenuation of 68dB.
The Copper attenuator has a maximum attenuation of 71dB.

As for the previous measurements I used the HP 8657B as the 'standard' against which to compare.

I also used a 0dBm input level for the 71dB (copper attenuator) and 68dB (Big attenuator) measurements in order to move the measurements comfortably up from the lower end of the Power Meter measuring capability. The Power Meter in fact showed a consistent slope ranging from 20.5mV/dB for 1.6MHz to 19.69 mV/dB at 450 MHz. Quite cool for a homebrew power meter!

Reference the following links:

68dB slope calculation

Insertion Loss Measurements

Maximum Attenuation Measurements

In conclusion both attenuators show significant insertion loss and maximum attenuator errors for the 148MHz, 224MHz and 450MHz measurements.

'BIG' Attenuator

'Copper' Attenuator

Homebrew Attenuator Measurements contd/

Today I characterized another attenuator recently acquired and known as the 'BIG' attenuator on this blog. The performance of this attenuator over the HF frequency band is not as good as the 'copper' attenuator (results shown in the previous blog). The worst case measurement was on one of the 20dB pads at +1.06dB error. Although this unit is solidly constructed, I assume that the fact that it does not have shielded compartments between each attenuator must degrade performance over the frequency range. Perhaps also the switches used are not as good as slide switches for this application.

The shown measurements in fact are optimistic since they do not include insertion loss. I performed separate insertion loss measurements which are shown in the next blog.

As a part of these measurements I also characterized the slope of the Power Meter.

In conclusion, the attenuator certainly is useful for many functions at HF. Also the use of 1/4 Watt resistors will allow use in higher power applications.

The following links

Measured Attenuation

Pi network resistor values and calculations

Slope Calculations

07 January 2015

Homebrew Attenuator Measurements

I recently acquired a homebrew attenuator (called the copper attenuator in this blog). The construction is modeled in line with the QST article of September 1982 titled "A Step Attenuator You Can Build" by Bob Shriner WA0UZO and Paul Pagel N1FB although the named attenuator pad values were different.

On opening up the unit I was mystified by the values used for four of the PADS. The parallel and series values appeared to have been transposed in error. I reworked these values using standard nearest value resistors.

The switches are in excellent condition with no signs of wear. As can be seen from the linked spreadsheets below, I tested the attenuator over the HF frequency range only. A maximum of 0.1dB insertion loss was observed at 28MHz.

The worst case error observed was +0.4dB for the 16dB PAD.

With all PADS switched in to yield a maximum attenuation of 71dB the maximum error was 0.8dB at 10MHz.

Click on the link below for details of the measurements made. To return to this page please use the back button.
Attenuator Measurements

Click on the link below for details of the resistor Pi Network Values. To return to this page please use the back button.
Pi Network Resistor Values, dB(calculated), Return Loss (calculated)