Ripples in the Ether

Audio Amplifier Guts

As I mentioned in a previous post a few days ago, I found a nice 2 watt mono audio amplifier board that’s a perfect addition to give speaker capability to a receiver with headphone output. I purchased four of these bad boys since they were so inexpensive (and I was paying for shipping from Hong Kong, so might as well order in bulk). I figured a good test would be to build up a bench amplifier so I could have the convenience of listening to any of my homebrewed phones-only receivers/transceivers (most of them) on speaker.

To the right, you can see the pleasing results of this little project. I had a nice Ten-Tec TPC-17 that turned out to be a perfect enclosure. The 1/8″ input connector is on the left, a power LED in the middle, and a mute switch on the right (the amplifier board has an active low mute line which works extremely well). I created a speaker grille drill template in Inkscape for the 3″ speaker bolted to the top lid of the enclosure (if there’s any demand for this file, I can post it here). The actual 1″ x 1″ audio amp board is on the left and a small 7805 voltage regulator board on the right.

AF Amp on the Bench

Here’s the enclosure all buttoned up for use. You can see that the speaker grille is a bit ugly, but it works well enough. There is no power switch, since the quiescent current is so low that there’s no problem in leaving it powered up. Tonight I hooked it up to my VRX-1 (with a rock on 7030) and listened to the wide-open band with the DX contest in full swing. The audio quality was quite nice; better than I remember it when testing it out in the open on the workbench. I’m guessing this is because the speaker was properly mounted instead of having the magnet rattling against the bench. Even though it’s a simple project, it’s a great addition to the shack that makes me wonder why I didn’t do this earlier. Yeah, I could have purchased a set of amplified PC speakers, but that just didn’t seem appropriate. Besides, the amp in the Ten-Tec enclosure looks spiffy next to all of the other similar looking equipment in my shack.

Update

I got a bit bored tonight, so I took a video to demonstrate the amplifier working with the VRX-1. Yes, I know there’s nothing to really look at, but the audio is a bit interesting.

I’ve noted with quite a bit of interest the recent surge of comments on QRP-L favoring a QRP exodus up from 7030/7040 kHz to [part of] the old Novice watering hole of 7100 to 7125 kHz. The esteemed Arnie Coro, CO2KK seems to have ignited the fire with this post to the reflector:

Dear amigos :
The 40 meters band changed last year … when the worldwide assignment for ITU Regions I, II and III was finally made totally compatible for the first 200 kiloHertz. According to what we have learned here, this was a difficult to work out agreement, but at the end
thanks to the presence of radio amateurs sitting as members of many of
the nation’s delegations attending the ITU WARC… it became a reality…
So, now we have the 7100 to 7200 segment for radio amateurs exclusive use. My understanding is that the US FCC decided to expand the 40 meter phone band down to 7125 kiloHertz…
That leaves the segment from 7100 to 7125 kiloHertz quite useable for CW…
My suggestion is to start using 7105 or 7110 kiloHertz as the QRP
meeting frequency, replacing 7030 and 7040 kiloHertz that are under so much QRM, especially from digital modes. I agree that many stations have already equipment with crystals for either 7030 or
7040 kHz… but for those of us with VFO capability, enjoying the much
more clear channels between 7105 and 7110 kHz opens up the possibility of many more QRM free QSO’s…
My observations carried on during the past several days confirm that
that segment of 40 meters right next to 7100 is clear much of the time  !
Let’s give it a try !!!

73 and DX
Arnie Coro
CO2KK

The positive response to Arnie’s call to action was immensely gratifying to me. In addition to all of the reflector replies, there have also been some ham bloggers taking up the topic. I’ve long been a fan of this little slice of bandwidth, but at times it has been hard to scare up contacts there. In the last couple of years, SKCC has probably been making the most extensive use of the sub-band, which has increased the traffic there a fair amount and has brought more attention to the frequencies as a place to have a nice, relaxed CW QSO.

Not to long ago, I dreamed about ways to help increase the use of these frequencies, and even started chatting with a few other hams about ways to spark some interest. However, like a whole lot of my ideas, they never get off the launchpad since I just don’t have the time to invest in all of them. After having a few unpleasant encounters with RTTY contesters running me off 40 meter frequencies last weekend, I’m even more determined to help promote 7100-7125 as a QRP (and general CW) safe spot.

I’ve become inspired enough that I’ve decided to take a new design for a minimalistic superhet rig that I’m working on and adapt it to operate on these frequencies. If there’s any interest in it, I might even take a crack at offering it as a kit for purchase. Long live 40 meter QRP!

This weekend, I’ve been participating in the SKCC Weekend Sprint when I get the opportunity in between other obligations. At about 0900 local, I heard F6HKA on 20 meters coming in pretty well with a very fluttery signal. As you can see on the azimuth map for my QTH, the path to France goes right over Greenland, so it’s not a huge stretch to assume that the unique signal quality is due to auroral effects from the increasingly active Sun.

After about an hour of trying, I finally managed to snag a QSO with Bert using 5 watts! A great day for QRP!

F6HKA-1811-14-Feb-2010-14046.mp3

Take a listen to this QSO which was recorded a bit before I made my contact with F6HKA. You can definitely hear the watery, fluttery sound of his signal.

Sure Electronics EUA2005 Audio Amplifer Lash-Up

Lately, I’ve found that eBay has been one of the best ways to beef up my junk box with inexpensive electronics components (eBay Stores are my preference, the auctions often aren’t that great). I purchased a nice SMD resistor/cap assortment from a company called Sure Electronics and found that they have some other goodies that might be of interest to the homebrewer. One of those is a tiny little (about 1″ x 1″) 2 watt mono audio amplifier based on the EUA2005 IC. The spec sheet states that the IC output power is 1.5 watts, so the manufacturer might be fibbing a bit on their specs. Regardless, it’s enough power to drive a 3″ speaker to a decent volume for shack listening. The IC has a maximum V_CC of 6 V, so I had to create voltage regulator to step my 12 V bench supply down to 5 V using a 7805. The audio quality is definitely what I would call “communications” grade, but the price is great: $2.22 for a 2-pack. One word of warning: your order is shipped from Hong Kong, so expect about 2-3 weeks for your order to arrive.

For those working on W8DIZ’s frequency counter project in QQ, they also have a Atmel STK500 in-circuit programmer clone for a very inexpensive price. I haven’t had a chance to try mine out yet, but if it works as advertised it’s well worth the price (I have no reason to believe that it won’t work, but if doesn’t, I will update this post).

The usual disclaimer applies: I’m not associated with the company in any way, just a satisfied customer.

I’m very pleased to report the first (to my knowledge) completed Willamette transceiver which was born in Europe. Vincenzo, IZ5GVP sent along to me a couple of photos of his very nicely constructed Willamette. He reports that it works well and that he’s considering modifying it to operate on the 30 meter band. Three cheers for Vincenzo!