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E-mail: Jack.Smith@cliftonlaboratories.com
 

 

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October 2010 Archives

 

23 October 2010

One of the revised printed circuit boards I mentioned a few days ago is a new kit, the Z10042AV Norton amplifier. You can read the instruction manual by clicking here or through the Z10042AV page.

I've had few requests for a Norton amplifier usable well into the VLF range, from 3-30 KHz. The Z10040B Norton amplifier has a lower -3 dB point around 60 KHz and the Z10042A improves this to 45 KHz.

The Z10042AV drops the lower -3 dB point to around 16 KHz. This should meet the requests for a lower -3 dB point.

Reducing the lower -3 dB point turned out to not be a simple task. Several seemingly simple changes are needed to move the lower corner frequency down:

  1. Feedback transformers T2 & T4 need more primary inductance
  2. RF choke impedance must be increased
  3. Input and output transformer magnetizing inductance must be increased

Modifications 1 and 3 are not too difficult.

Modification 1:The Z10042A Norton Amplifier uses a 1:11:4 transformer turns ratio for 12 dB nominal gain (11.4 dB realized in practice). Doubling all turns to 2:22:8 preserves the gain factor, but quadruples the primary inductance. The negative side of doubled turns is that the feedback transformers have increased turn-to-turn capacitance, which reduces the high frequency response, with an upper -3 dB point of 20 MHz, compared with 46 MHz typically seen in the Z10042A.

Modification 2: The Z10042A uses physically small 1mH shielded RF chokes, API Delevan's SDS-680 series. To improve low frequency performance, the emitter chokes should be 2.2mH and the collector chokes (at a higher impedance point than the emitter) should be 3.3 mH. Although SDS-680 series parts are available in both values, their inductance drop with DC current produces unsatisfactory results. Hence the Z10042AV uses Coilcraft LPS-6235 shielded chokes with a higher DC current rating. Since the LPS-6235 parts are physically larger than the SDS-680 inductors, I found it necessary to revise the PCB layout. While revising the layout, I made a few other changes to the board, including:

  • Almost all parts are now surface mount.
  • DC power is now provided with a female connector to avoid exposed DC pins
  • Modified DC power circuit to always use the 1mH isolation inductor whether power is provided over the coaxial output (duplex power) or directly.
  • Cleaned up a few untidy traces and pad locations and added silk screen connector information.

Modification 3: The input and output transformers are increased from 10 bifilar turns to 18 bifilar turns, more than tripling the magnetizing inductance.

The new PCB layout also is easier to build as it reduces parts crowding around Q1 and Q2 by moving more components to the bottom surface and revised trace routing.

The Z10042A has identical physical dimensions with the Z10042A and uses the same mounting holes. Hence it fits the custom powder coated enclosure developed for the Z10042A and Z10046A amplifiers.

The Z10042AV is the same price as the Z10042A and is available for immediate shipping.
 


Clifton Laboratories now has four amplifiers available for sale.
 

Amplifier

1 MHz Gain (dB)

Lower
 -3 dB

Upper
 -3 dB

Amplifier Type

Z10040B

11.1

61.0 KHz

46.6 MHz

Norton Amplifier; through hole design

Z10042A

11.2

45.1 KHz

46.0 MHz

Norton Amplifier, mostly surface mount design

Z10042AV

11.5

16.0 KHz

20.8 MHz

Norton Amplifier, almost all surface mount, with improved low frequency response.

Z10046A

23.7

28.6 KHz

61.8 MHz

Quad GaLi-74+ MMIC amplifiers in push-pull/parallel.

23 October 2010

 

16 October 2010

I've received the revised printed circuit boards mentioned on 04 October and have been busy building and verifying the layouts.

I've also started on a long delayed project, an antenna multi-coupler. In the best case, it's a month or more from being ready, but I hope to have it completed and orderable before the end of the year.

I've added a new page 19.8 KHz showing signal observations made by K8AQC in suburban Detroit of the Australian VLF station, NWC, operating on 19.8 KHz. Ron uses a Z1501D Active Antenna. The animated image at the web page shows nicely how the signal and noise varies over the observation period from 5 AM to 10 AM local (eastern time) observation period.

 

04 October 2010

As usual, the prior month's updates are moved to an archive page, reachable by clicking here or from the navigation box at the top of this page.

I've been busy working on some housekeeping chores with respect to my kits, making some changes to several of the printed circuit boards to better standardize on parts and taking advantage of things I've learned about board layout. No performance changes with the existing kits, but more a tidying up.