Thursday, December 20, 2007
Wednesday, December 19, 2007
Monday, November 26, 2007
I found this to be a big help. The QF-1 effectively eliminated the CW audio image (ie. a readable signal each side of zero beat) common in receivers that don't have a crystal filter. Eliminatling the audio image eliminated half the QRM on the band.
Wednesday, November 21, 2007
http://www.io.com/~nielw/nat_list/nc57.htm for more information.
My set had been already gone through by a previous owner, recapped and aligned. This set includes an extra dial string in the bandspread tuning assembly to overcome slipping. While this radio generally worked it also would go dead once and a while for no apparent reason. Close inspection revealed a cracked solder connection on a filament pin of the 6H6 detector. Resoldering this connection fixed the problem.
Properly aligned, the calibration was excellent and sensitivity good but this radio is still only one step removed from a simple SWL receiver. Mechanical and electrical stability is marginal, especially above 40 mtrs. It was no surprise that SSB and CW signals easily overloaded the receiver and BFO. Operation with the BFO requires running the AF gain wide open and controlling volume with the RF gain control. I did like the positive feel of the main tuning. While National used a failure prone dial string for bandspread tuning, main tuning uses a gear/pinch wheel mechanism.
Three years after introducing the NC-57 National came out with the NC-125. Under the covers this "new" receiver was simply a NC-57 with the internal speaker replaced by an S-meter and Select-O-Ject audio filter. Both of these features were available as options on the NC-57. National also replaced the round dials with slide rule dials. Unfortunately National took a step backwards by using slip prone dial strings on both the bandspread and main tuning. The Select-O-Ject feature, while unique, does nothing to remove the audio image. I believe a Q-multiplier similar to the Heathkit QF-1 would have been more useful.
I acquired a tilt base with my NC-57. Besides tilting the radio front for easier reading, this also allows a ham to add extra station controls and some accessories without cluttering up the shack. High on my list is a 1MHz crystal calibrator to help set the main tuning for repeatable bandspread calibration over each ham band.
I plan to use my NC-57 on 80 and 40 with one of my early novice transmitters.
Sunday, October 28, 2007
On October 26 I finally had a chance to do some more K1/QRP operating. This time while on a trip to Austin, TX. The weather was great: sunny and about 75. My antenna was again a 67' (full wavelength on 20 mtrs) endfed wire . The operating position was on second floor balcony. I ended up running my antenna up to eaves above me and then sloping down to a fence along side the yard. My clear view was to the east and I was on top of a bluff over looking Lake Travis.
A few minutes before noon I had a QSO started with KC9AWL, Len, in Palm Coast, FL on 14.057. He gave me a 559 but when I noted how deep the QSB/fades were I knew we were in trouble. Len turned it over to me but, evidently, the band went south and he lost me. I never heard him a second time.
Within ten minutes I had another QSO going on 14.057, this time with WA9FZP, Phil, in Racine, WI. This enjoyable QSO lasted about 1/2 hour with 559-569 signals the entire time.
Sunday, August 26, 2007
Tests on 40 meters have been a little disappointing. The 815 runs at only 35%-40% effeciency into a 50 ohm load. 50 watts input gives only about 20 watts out. (whoops! I checked my Drake watt meter agains a Bird. Turns out that the Drake watt meter is reading way low. The Bird says I'm putting out about 30 watts. This is about the power output I expected.) Also the transmitter is not real forgiving. If misadjusted, it goes into self oscillation or generates a trashy sounding signal.
This one will go to the back of the shelf. (but after discovering the watt meter error, only while it waits for a power supply)
Friday, July 6, 2007
Tuesday, June 26, 2007
Monday, June 25, 2007
On the 815 transmitter front it needs a better regulated suppy for both the 815 screen and the oscillator plate. The dropping resistors have to go.
Monday, May 28, 2007
I have a working 815 transmitter. Unfortunately I had to "glue" a capacitor on to the side of the chassis to do it. Key to getting the final to work into a variety of loads is some sort of antenna tuner. Adding a capacitor into the grounded side of the output link does just that. The added capacitor does output loading . Tune up now amounts dipping the final with C2 and increasing/decreasing the loading with the added output link capacitor. Typical operation is 50 watts input and 35 watts out.
Eventually the loading capacitor will be hidden behind a front panel.
Friday, May 25, 2007
On the homebrew 815 transmitter front I've been trying to get the final coil wound so that the transmitter delivers full output to a 50 ohm load. At this point I'm about to add an outboard antenna tuner to my project list.
Monday, May 7, 2007
I've powered my new transmitter up on 40 meters.
For use during this test phase I built an adapter to allow the use of B&W 5 pin JVL transmitter coils instead of winding coils on my National coil forms. I'm also temporarily connecting the bias and voltage dropping resistor networks to the back 12 terminal barrier strip. This way I can easily play with the resistor values to get the right voltages.
The transmitter loads up to 40 watts input and 30 watts output with no sign of self oscillation
I've still problems, though. The 815 screen current won't come down. It appears to draw around 60 mA rather than 15. High screen current causes the screen dissipation to be exceeded, maybe damaging the 815. Right now I'm looking for another 815 to compare readings with.
Sunday, May 6, 2007
I aquired another radio last week. This one I "won" through ebay. The pictures posted on ebay showed a fairly ughly set with three mis-matched dials. The layout, though, suggested the "Three Tube Regenerative Receiver of Unusual Performance" by George Grammer and written up in the January 1933 issue of QST.
I bid and the gamble paid off. Underneath the flaking paint front panel and cabinet was a fairly nicely done version of George Grammer's design.
George grammer's original article was more than another construction project. He spent a large part of the article talking about features of good regen receiver design before describing "a practical receiver". This receiver includes a tuned RF stage and general coverage/bandspread tuning. Bandspread tuning is via the drum dial at the left after the detector and RF stage bandset capacitors are set. The receiver showed up in the ARRL handbooks through 1937.
Wednesday, April 25, 2007
L1 of my transmitter calls for ten turns on a 1" coil form spaced over 7/8". I had the form and the wire I needed. Winding spaced turns, though, takes a trick. I first wound the ten turn coil on the form, tightening the wire as much as possible. The turns were not even. It was not pretty. I then wound another "coil" (the red wire) forcing evenything to space out evenly over the 7/8". This I heavily coated with clear fingernail polish. After the fingernail polish had dryed I removed the red spacer coil and recoated with fingernail polish.
Monday, April 23, 2007
We spent the weekend in Decorah, IA and on Saturday and Sunday I had some spare time for hamming. I used my K1 with a 67' endfed wire up in the tree above the campsite. With the K1's built-in antenna tuner it loaded up on 40, 30 and 20. Sunday afternoon at 3:00 I did finally did have a QSO with Ken, WA8REI/4. He was on the Appalachian Trail at Newfound Gap, NC near Gatlinburg, TN. We were on 14.060, both running battery/5 watt power into end fed wire antennas. With some amount of QSB, signals were around 579. For the bottom of the sunspot cycle I was pretty happy.
See more examples of my QRP operating at http://www.io.com/~nielw/qrp/QRP_Stn.htm
Monday, April 9, 2007
I've finally committed to a layout and mounted the major parts. From left to right along the front is the xtal (with B directly above it) C1 and C2. Left to right on top is 6V6, L2/L3, 815 and L4. RFC2 is mounted upright behind the 815 and L4. I elevated L2/L3 so that it could be mounted directly above C1. The toggle switch on top of the chassis in the right front corner is to short out L1 when not multipling in the tri-tet oscillator. The extra space along the back is reserved for whatever is needed to get the screen and oscillator voltages right. The spotting switch will probably go in the space between C1 and C2 with a cathode current meter mounted directly above it (if I add a front panel).
Saturday, April 7, 2007
Thursday, April 5, 2007
"It's an easy way to obtain high- and low-B+ voltage sources. In fact, there's more than one way to skin a cat... center tapped or non-center tapped transformer using a fullwave doubler. In both cases, the output voltages differ by a factor of 2. The doubler, aside from needing a transformer with only a single secondary winding, has the advantage that the output voltage is 2.828 RMS instead of only 1.414 RMS. So, your secondary can be 177VRMS instead of 354VRMS. Practically speaking, because of resistance losses, the voltage would be somewhat lower under load. And of course, you'd still need whatever VA rating, so the transformer size/weight would be the same.
With either topology, you'll have a significantly lower low-B+, and should you decide to use a regulator, will not have to dissipate as much power in the series resistor."
Wednesday, April 4, 2007
Tuesday, April 3, 2007
The first Tuesday of the month is informal meeting day at W0IBM, Rochester, MN. ( see http://www.w0ibm.org/ ) I took along my K1 as show and tell. 20 wasn't real active but I hooked up to the W0IBM three element yagi and managed a contact with George, KF4UCC, in Chesapeake, VA.
On the 815 transmitter front I've done a rough layout to help orient tube sockets and studied the dimensions a bit more. It still looks like it will fit. I'm just about ready put the drill to that virgin chassis.
Wednesday, March 28, 2007
Sunday, March 25, 2007
To add a spotting switch to the 815 transmitter I'll try a DPDT switch connected in the cathode circuits of both the oscillator and the final. In the "spot" position it will key the oscillator just as the key and also open the cathode-to-ground connection on the 815. The crystal oscillator should operate normally letting me locate myself in the band but I'll not have 50 watts of RF overloading my receiver.
Thursday, March 22, 2007
Wednesday, March 21, 2007
Tuesday, March 20, 2007
Monday, March 19, 2007
I'm to the point of starting to layout my 815 transmitter. Here are a couple of figures from the 1943 ARRL handbook describing this transmitter along with a picture of my preliminary layout. My chassis is 3"x 8"x12" so I have a little more room. Good thing, since I didn't have the small size variable caps called out in the original design. I'm also allowing room for a VR150 (seen on the back left corner) in case the oscillator stage needs regulated B+ for stability. The original design used only 3.5MHz crytals to cover 80, 40 and 20. I'm going to use 3.5 MHz crystals on 80, 7MHz crystals on 40 and 7MHz crystals on 20. This leads to one change. I'm adding a switch across L1/C3. This will be used to short out the cathode coil/cap when I'm running the tri-tet oscillator straight through.