Old Spark (But Thankfully Not Forever)

For the last couple of weeks I have been plagued by noise on the HF bands.  In spite of being in a very built-up area of Northern Virginia,  I usually have low noise levels.  But for the last couple of weeks I've had intermittent but frequent arcing noise.  It sounded like classic power line arcing. 

My 17 meter Moxon antenna provided a clue as to where it was coming from:  As I spun the antenna around, the noise was always a lot stronger to the North-North West.

On Wednesday morning on the way to work I noticed that the fire department and the power utility were working frantically on a pole about a mile from our house.  It had obviously been on fire -- it was still smoking when we went past.

When I got home I was pleasantly surprised to find the arcing noise gone.  It took me a few minutes to make the connection -- yes, the smoking power pole was to my North-North West. 

OBVIOUSLY THE RADIO GODS CAME TO MY ASSISTANCE!

This was a good demonstration of the fine front-to-back characteristic of the Moxon antenna.  And a reminder of what radio signals sounded like in the days of spark. 

The 9CS transmitter (from http://www.ontheshortwaves.com/EarlyAmateur.html)

  

Bryan KV4ZS's "Let's Build Something" Direct Conversion Receiver

Bryan: 

 

I think it sounds great!  There is nothing really wrong with it -- that is what 40 meters sounds like!   Sure there is static.  And those whistles you hear near the top of the band are the carriers from shortwave broadcast stations.  You might have a little hum, but that should disappear once you get it all packaged in a metal box.   Congratulations Bryan!  You have done something that very few hams have done:  You have built a receiver. 73  Bill N2CQR

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Hi Bryan,

 

First let me congratulate you. That is one fine build and you may actually have absolutely nothing wrong!!!!!! I really must applaud your “squares”. They look like they were made on a CNC machine. Bravo!!!

 

You are operating the LBS without an RF amplifier and as such you are trying to make up the gain in the audio amp. I would say that the results you are hearing are very consistent with the DCR without an RF amp. Get the RF amps stage working and then run your test –you will find with the RF amp that at the gain setting you have for the video will be room filling. It actually sounds pretty good. You might also try connecting a 1 NF across the audio trimmer pot as that will cut down on the “hiss’ sound.

 

Concentrate on the RF amp stage and then re-run your test –you will see the difference.

 

Great build – very nice job.

 

73’s

Pete N6QW

 

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Very nice!

 

Sounds pretty good to me in terms of noise – that’s what a direct conversion receiver sounds like (they tend to be very wide in terms of reception – static is normal... Welcome the world without noise reduction and DSP!!).  DCR’s – because they are not run through a narrow IF filter – allow a very broad range of signals to get to the audio stage. So, for example, if you tune that around during a CW contest, you’ll hear a LOT of signals at the same time – versus only one or two at a time, once you have this run through the 4.9152 crystal filter. That’s the nature of the beast.

 

The 1nf across the audio trimmer definitely will help with reducing the hiss, although I must say my Kenwood receivers all have a similar amount of hiss and I prefer my radios with more, not less, noise (it lets me know what the band conditions are like...). I have noticed on my builds, however, that if you have a very, very high pitch WHINE on the other hand, that tends to be a bad solder joint or bad capacitor somewhere – probably on a capacitor – introducing an offset into your RF someplace it shouldn’t. What that looks like on an oscilloscope is the audio signal will have a large DC offset versus ground – almost always a bad solder joint on a capacitor—or a bad/broken capacitor--somewhere in the audio amplifier. That’s the same problem you get when you try to record audio sometimes from an external source (TV, radio, CD player) on your computer – DC voltage offset on the audio line. Kind of like what you might have heard on a stereo if you ever tried to switch to a channel where the input was hanging open.

 

Ben

KK6FUT

Alan Wolke in the Dinosaur Den (Video)

Very cool.  But it makes me sad that my Tek 465 broke (and I can't fix it!).

Jac's Homebrew Receiver (video)

 

Jac (KA1WI) and I spoke on 40 meters on June 29th.  I told him about the BITX -- he said he liked the idea of building something and pledged to start melting solder.  This week I got this message and video from him.  Good going Jac!  That was fast! I think we all know who designed the IF amp:  Wes W7ZOI.   As for the DS/PLL, I recommend you take a look at the Si5351 with an Arduino microcontroller.

Hi Bill,

 

I started in July building a receiver with the available parts I had collected over many years. Finally today the receiver is working more or less to my satisfaction. Here is a brief description. 

 

I am using a set of crystall filters from an old Atlas 350XL, 5.595 is the IF frequency and the filters  have independent USB and LSB plus CW 500 Hz filter. The radio set is a single conversion type. A DBM at the front end and as product detector. Keeping the BFO signal from leaking is a challenge but I managed by carefully matching the three ports of the DBM used as product detector. Matching the IF filters impedance was another challenge. Following the DBM there is a LNA amplifier using a 2N3866 and I am trying another LNA with a discontinued Siemens BFT66 transistor with a very low noise figure. I have some experience with those and they can be amazingly quite. 

 

The IF amp is a hybrid cascode with three stages and AGC that I found in the internet designed by a well known  OM, the design works very well it is easy to make and is very stable despite its nearly 70 dB of wide band gain. The AGC range is close to 100dB . . .

 

The front end has 6 BPF covering from 1.5 to 30 Mhz all switched by relays. This unit I got from an old German receiver. 

 

The VFO or 1st LO is a DDS unit I had played with years ago. From N3ZI is far from perfection but it does the job when the bands are alive and well. The alternative to the simple DDS are complicated. I wish there were more DDS PLL kits available. It can take a long time to get a full synthesizer satisfactorally working. 

 

The set is made of mechanical parts from a Tektronix main frame instrument, there are many parts of different shapes that can be attached together in a crazy way but certainly very functionally. There is the IF amplifier and the Product Detector BFO enclosed in two brass silver plated boxes, both also recovered from some surplus ages ago. The DDS is one of the sides on the chassis without any shielding.

 

The IF filters and the front end are going to be attached to the rear of the chassis by just adding brackets etc., you get the idea. I am glad the video is acceptable.  

 

I thought it will interest you know that at age 70 is also possible to roll your own, despite having to check every solder joint since my eye sight is the biggest  problem 

 

I have other projects, another receiver with an IF of 9 mHz with SSB and AM filters using another type of high gain IF amp. 

 

Best 73’s de 

Jac
 

First Ever SSB Homebrew to Homebrew Contact by N2CQR. With...

2322 miles.  3737 kilometers

Pete Juliano and I were talking on Skype yesterday evening.  He was regaling me with tales of the wonders of his new beam antenna.  He mentioned that he was working a lot of East Coast stations... Wait a minute, I thought, I'm an East Coast station.  And I have a 20 meter rig sitting right in front of me.  "Meet me on 14.190 Pete!"   It took me a minute or so to get the rig connected to the CCI amplifier and the 20 meter dipole.  By the time I got everything fired up, there was a station on the frequency.  I thought we'd lost the spot.  But no!  I realized it was Pete calling me. 

This was extremely cool.  Pete was using his ZIA rig with the brand new beam.  I was on my VFO BITX20.  And I was using the CCI amp that Pete had coached me on (he taught me how to tap the holes for the heat sink).

This was the first time I had ever contacted another homebrew SSB station -- and the first time Pete and I had spoken on the air.  THE RADIO GODS WANTED THIS ONE TO HAPPEN! 

I recorded the QSO:

http://soldersmoke.com/n6qwn2cqr.mp3

I will ask Pete to provide more detail regarding the California end of this QSO in the comment section below.  Did you have your amplifier on Pete?