A single-transistor 16 dB gain RF amplifier

Here are two photos of an RF amplifier built by KE4ID using the popular bug construction. (Click on each image to enlarge.) The use of a readily-available metal box saves cost and provides a convenient ground plane to which components can be directly soldered for grounding and mechanical support. The circuit is based partly on designs published by KK7B in QST and in the ARRL book Experimental Methods in RF Design.

Jack loaned this amplifier to me for evaluation as an interface between a stand-alone Yaesu digital VFO and my Heathkit SB-104A transceiver. I'm in the process of breadboarding a similar unit for this function. The output of the Yaesu VFO needs to be boosted to 3 V p-p to match what the Heathkit internal VFO provides. An existing jack for an external VFO makes the connection to the Heathkit convenient. The goal is to obtain a more stable and precise frequency control than what is possible with the internal analog VFO.

Here is the schematic diagram.(Click to enlarge.)

Telephone Pioneer QSO Party - Results & Announcement

The Telephone Pioneer QSO Party web site now has the results and discussion for the 2011 event, which was held in October for the first time. Once again W4BXI was very close to N6TP's top score. W4AXO was also among the top participants.

The above web site will also soon include an announcement about the 2012 event, which will take place on October 20-21.

Bell Ringers at BirmingHAMfest

BirmingHAMfest
Sponsored by Birmingham Amateur Radio Club
March 3-4, 2012
Bell Ringers / TPARCA forum
Saturday, March 3, 10:00 am @ Divan Room, first floor
Members, friends, family welcome

SWR: Does it matter?

SWR and baluns were discussed during several of our recent morning QSOs. We combined personal experiences and many on-line references in order to better appreciate the topic.

• Understanding SWR by Example by K5DVW is a must-read article. (You can skip the Smith Chart section.) The article illustrates how transmission line loss can easily be a greater issue than SWR when trying to transfer maximum power to the antenna. 
• VSWR Myths includes a similar set of examples and goes on to discuss various common myths. 
• The Easy Way is a wordy article that also makes the case for non-resonant antennas and tuners to operate across multiple HF bands. Four topics covered in separate sections of the article are: Antennas of non-resonant length, Line attenuation,the Transmatch, and the Balun.

A few online calculators enable you to estimate the losses due to SWR:

• SWR Loss Calculator
• Types of Coax Cable and Line Loss
• Misunderstanding VSWR misleads - This article discusses some pitfalls of such calculators and provides a link to a more sophisticated calculator. Look for TWLLC on that page.

Many articles explore the use of baluns in all sorts of HF antennas:

• Choosing the Correct Balun by W8JI provides guidelines for several antenna types. An area of particular interest in our group discussions is the multi-band  dipole with balanced feeder. A table in this article includes recommended element and feed line dimensions. I found a second version of this article that has a copy of Table 1 with data for both 300-ohm and 450-ohm feeders.W8JI has lots of other content on his web site.
• Baluns in Antenna Systems by VK1OD analyzes several balun usage scenarios and compares their modeled behaviors, with conclusions for each. Other references are provided. The author's home page has links to lots of content.
• Baluns: What They Do and How They Do It by W7EL gives a detailed explanation, with sketches, of what issues a balun is intended to solve. The article includes the results of field experiments to support conclusions about balun use, but also with further questions. W7EL is the author of EZNEC software.

Finally, from G4NVH comes HF Balanced Transmitting Systems, a 75-page compilation of materials from various sources. See the table of contents and pick your favorite topics!


John

Visit to KB4LWT

Here are photos from Gary N4OLN's visit to Larry KB4LWT. The outdoor photos show some views of Larry's loop antenna.

Hunter Bandit Linear Refurb by N4MYT

Click here for a report from N4MYT about the power supply refurbishment of his Hunter Bandit linear amp.

Here are photos from W4BBW taken at this summer's reenactment festivities at Ider, AL.