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August 2009

 

29 August 2009

I've made a few small changes to the Z10040B Norton amplifier printed circuit  board and the current version is rev 02. I've updated the instruction manual to reflect the PCB changes. The new manual may be downloaded here or from my Documents page or via the link at the Z10040 page.

 

25 August 2009

I've started work on an article for QEX concerning capacitor selection for various purposes. One part of the article involves measured capacitor Q to determine the capacitor type suitability for filters or carrying RF current. While I have a reasonably complete selection of modern through hole and surface mount parts either on hand or on order, I thought it would  be useful to include the old stand-by, the molded mica as a historical comparison. I believe these are long since out of production, but still show up in surplus and in builder's junk boxes.

I've searched my collection of old micas, and found it rather short. What I would like is one or two WW II era "postage stamp" as well as the (1950's and 60's) smaller rectangular molded mica capacitors in roughly the following values:

33 pF
100 pF
330 pF

These are the value of the modern ceramic, dipped silvered mica and film capacitors I've selected as measurement candidates based on the range of values common in HF radio projects.

If any reader has spare old-style micas in roughly these values, and would care to have it used in my project, please drop me a note. I'll cover your postage and the reasonable value of the parts.

At the moment, my plans are to analyze:

  • General purpose dipped silvered mica (through hole epoxy case)
  • Surface mount mica for  RF use
  • NP0 ceramic - general purpose (through hole and surface mount)
  • NP0 ceramic high-Q RF option (surface mount only)
  • PET film
  • PP film
  • PPS film

Any others I should include?

I've tried to get both surface mount and through hole parts, but not all dielectrics are readily available in all styles. And I would like to stick to parts that are within the typical builder's budget, as well as my budget for purchasing parts. Some of these parts approach $5.00 in single lot quantities which was my more-or-less arbitrary cutoff point as something that might be justifiable to used in an amateur radio project, recognizing that this level of price will have to be supported by extraordinary performance. Or, more likely, the parts in question being available on the surplus market. I've decided not to include parts that are cost-justified only when found on the surplus market because their availability is so hit and miss, although, of course, that's a great way to find a few high performance odds and ends that otherwise would not be used.

I know film capacitors are not usually recommended to be used above a MHz or so,  but thought they would be useful as a comparison.

I've also found a high-Q RF version through hole dipped silvered mica in CDE's catalog but can't find a supplier without a rather high minimum order quantity.

The article is likely to be some time in completion as I have many more aspects to cover. And, following the old adage that "a day in the library is worth a month in the laboratory" I've given the Burke Center branch of the Fairfax County Public Library a workout in obtaining books via Inter-library loan.
 

24 August 2009

I've added a comparison of measured data versus predicted for the simple three-element inductor model at Self-resonant frequency of Inductors.

 

23 August 2009

A question was recently posed on the Agilent equipment mailing list asking why a particular Agilent LCR meter showed an inductor with "negative inductance."

The short answer to the question is that above the self-resonant frequency of an inductor, it "looks like" a capacitor and since capacitance is negative inductance, it all makes perfect sense. Although short and correct, a more detailed discussion may be useful to those encountering for the first time the self-resonant frequency of an inductor.

I've added a page dealing with self-resonant frequency of inductors at Self-resonant frequency of Inductors.

 

22 August 2009

Accompanying my Z1501C active antenna kit is a DC power coupler to inject DC power over the coaxial cable to power the remote antenna (or a remote Z10040A or B Norton amplifier). I received the first run of printed circuit boards for the Z1203A DC power coupler Thursday and I built one this afternoon.

A few parts mount on the connectors (input RF and input DC) and hence don't appear on the PCB, but the photo  below shows a Z1203A completed PCB.

I will measure the insertion loss as a function of frequency tomorrow, but the prototype showed useful performance over the 30 KHz - 30 MHz spectrum plus some.

One feature in both the Z10040A and B Norton amplifiers and the Z1501C active antenna is a remote relay to disconnect the input when the amplifier power is removed. The Z1203A DC power coupler complements this feature with remote DC switching. Applying a positive DC voltage to a control input (or, by moving a jumper, grounding the control input) will shut down the coupler's output voltage and enable an active voltage "pull down" circuit. The purpose of this is to allow a transceiver's keying line to remove power from a remote Z10040A/B amplifier or Z1501C active antenna when transmitting. The active pull down circuit will speed up the remote disconnect relay's action by shunting  the disconnected DC power bus with a low value resistor, speeding up discharge of high value bypass capacitors in the remote amplifier or active antenna.

Although I have the Z1501C and Z1203A printed circuit boards on hand, I am waiting on the antenna bracket and Z1203A enclosure before releasing these kits. I hope the kits will be available before the end of September.

I built the board  with 3-pin headers but the kit will use wires soldered to the pads.

As usual with my kits, the board is double sided, silk screened and solder masked. The Z1203A kit will include a custom enclosure, finished in black powder coat paint with silk screen legends. The connectors are BNC (remote antenna/amplifier), RCA (control), 5.5/2.1 mm (DC power) and isolated BNC (to receiver). A DC power indicator LED is also provided.

The maximum current the Z1203A can pass to the remote antenna/amplifier is 200 mA. The Z1203A is for receiver use only and is not intended to be connected to a transmitter or other source of RF power > 100 mW.

 

Z1203A DC Power Coupler PCB

 
17 August 2009

Thanks to Tom, KM5H, I've had the opportunity to look at a Silicon Labs Si500 one-time programmable frequency "synthesizer on a chip"�details at The Curious Case of the Warbling Si500

The Si500 is undoubtedly satisfactory when used as a clock in a digital circuit. However, it is unsatisfactory when used as an oscillator in an amateur radio transmitter or receiver. The problem is short and intermediate term instability, to the point where I regard the Si500 as unusable.

 

11 August 2009

I've added a photo to my page on home made "Q-Dope" to show  the stratification of my mixture after a month or so of the bottle standing idle. Click here to view the modified page.

Whatever the un-dissolvable chalky color residue is, it has no material effect upon the electrical or mechanical properties of the coil retaining compound.

 

07 August 2009

I've added a new page Power Supply Noise with observations on noise in several inexpensive "wall wart" power supplies as well as four laboratory-type bench supplies.

 

02 August 2009

The "classic" book on ferrites is Snelling (Soft ferrites: properties and applications (2nd Ed.) by E. C Snelling)

Snelling's book is well worth reading if you have more than a passing interest in ferrites, but the price tag is in the stratosphere. When I looked a couple years ago, Amazon had one copy of the first edition listed at $395 and another copy of the first edition for $450, but no 2nd editions. I obtained a copy by inter-library loan a few years ago and photocopied a few key references.

A reader recently let me know that there's now a "lower cost" paperback edition of Snelling's book. It's $160, which is better than $395, but still out of range for me. Check Amazon.com under the title to find the paperback edition.

 

02 August 2009

I've been working on completing development of several new kits, although my rate of progress is slower than I might wish.

I've also added a new piece of test equipment to my shop, an HP 4192A impedance analyzer, circa 1982. The 4192A is still a very desirable piece of equipment, and fills a gap between vector network analyzers and RLC bridges. It measures impedance, or RLC values, between 5 Hz and 13 MHz. More usefully, it can accurately measure impedances (complex values, R and jX) into the hundreds of kilo ohm range. Vector network analyzers are not well suited for impedance measurement when the device under test presents an impedance below a few ohms or above a kilo ohm or so.

One feature of the 4192A is a built-in DC bias source. The plot below, with data collected by the 4192A operating under computer control over the GPIB interface, shows the variance in capacity with DC bias voltage for a typical bypass capacitor using Z5U ceramic dielectric. I've written about this before at Capacitor Voltage Change and the 4192A makes collecting this data much easier. I'm contemplating an article for submission to QEX looking at some lesser known capacitor issues and the 4192A will be quite useful in that effort.
 

 
02 August 2009

As usual, I've moved the July 2009 updates to an archive page, reachable by clicking here or via the navigation table at the top center of this page.