Messages

31

Equipment / Re: The WW2 Radio Shack

« on: April 28, 2019, 1612 UTC »

This is really cool!
I wish you best of luck with your adventures in restoring such a site, and I look forward to reading your book.

32

Equipment / Re: General Coverage Comms rxer down to 20KHz?

« on: January 18, 2019, 0259 UTC »

If you don't want to spend the big money on a Watkins Johnson and government/military receivers like that, and don't mind an older design, I've been using a Bearcat DX-1000 for years.

This is where selective level meters can really shine, if you are ok with an analog dial. my rycom 3121 was 120 dollars shipped. I haven't personally played with the Bearcat DX-1000, but other some even cheaper radios, can preform well in the right condition. I have a tecsun PL-880, and although it only goes down to 100 khz, I was surprised how good it can be if one is careful to not overload  the front end. I bet there are many receivers out there that can do well with careful use. 

33

Longwave Loggings / Re: Northern California Winter NDB Logs

« on: January 14, 2019, 2252 UTC »

I am almost certain I heard the carrier for the dryden beacon, but can not confirm it because the sidetones are too weak. I have been trying to get that one for a while.

34

Longwave Loggings / Re: Northern California Winter NDB Logs

« on: January 13, 2019, 0719 UTC »

spent a good amount of time doing a full alignment on my Rycom 3121A selective voltmeter, so I decided to give the digital readout a rest for the day and tuned it around
I used the same transformer coupled passive antenna I use with my other radios, and to my surprise snagged some new ndbs. That 100 Hz xtal filter really is sharp
YXL 346 SIOUX LOOKOUT ON CAN
BBD 380 BRADY                     TX USA
YL    395   LYNN LAKE           MB CAN
YPO 401 PEAWANUCK         ON CAN
YHD 413 DRYDEN                  ON CAN

These plus many I have already heard with other radios

35

Equipment / Re: General Coverage Comms rxer down to 20KHz?

« on: January 05, 2019, 0253 UTC »

Maybe this isnt what you are looking for, but if you look long enough on ebay you can find a preamplifier for a lock in. These are usually made by stanford research or princeton applied research (eg&g PARc).
These often have a 1 to 10 MEGohm full differential input, and will really bring a rather VLF deaf receiver to life, as in many cases the poor performance of some receivers in that range is just because of their lack of sensitivity.

Beware bandwidth limitations though, some of these have an upper frequency of a kilohertz or less. many, however, will go up to a couple hundred kilohertz.

PS. there are also transimpedance models that have near zero input impedance, and a gain between 10 KV per amp or 1GV per amp. these are good for loops

36

Equipment / Re: General Coverage Comms rxer down to 20KHz?

« on: January 03, 2019, 2204 UTC »

The Analog Devices AD797 is a fantastic choice for LF and VLF preamps.

37

Equipment / Re: General Coverage Comms rxer down to 20KHz?

« on: December 28, 2018, 1713 UTC »

The wj8718, 8716 and 8718-a don't all say they will go that low, but they probably will.  My 8718 specifies 500 KHz as the bottom end, but will tune down to 15 or so

38

The RF Workbench / Re: Simple DSB TX

« on: December 21, 2018, 1835 UTC »

for 100W pep, you would have to drive the carrier port with about 500 watts....kinda lossy.

old microwave transmitters often had a 20 or 50 watt VHF transmitter going to a passive diode multiplier and filter for a watt or 2 of rf output. not efficient, but at a time when microwave devices were not very good, more reliable.

I think this might be a really good technique for a very low power high reliability transmitter, like a QRSS beacon. but that negates the need for dsb modulation.
 I bet the DSB modulation could be REALLY linear though, with careful design

39

Huh? / Re: If great scientists had logos

« on: December 20, 2018, 1622 UTC »

did you find that somewhere? or create it?
Fantastic!

40

General Radio Discussion / Re: Custom ferrites

« on: December 19, 2018, 1949 UTC »

Flat bars would probably be about the easiest shape to make.
My biggest disadvantage is that commercial ferrites are pressed in custom machined steel die to many tons of pressure per square centimeter, I do not have access to such equipment, and even if I did, The cost of making a new die for a custom shape would necessitate selling many thousands of parts in that shape.  I am going to use the older laboratory method of slipcasting in plaster of paris molds. The difficulty is in preparing a slip that is only 25 to 35 percent liquid (probably water or alcohol) in which the dense ferrite particles will not settle out.  I have done this before with silicate minerals, but never ferrite.

PS. I dont really like trade secrets, so I will gladly share any process details I find or methods I use, when I try this.
Feel free to pm me if you have questions/advice/criticisms

41

General Radio Discussion / Re: Custom ferrites

« on: December 19, 2018, 0113 UTC »

Unfortunately, the chemical composition for the types are not always so easy to find, my best bet would be to make the same shape until its characteristics match. A 2 inch binocular core is what I actually thought would be a good choice, I have looked for potcores too in that size, but they are fantastically expensive unless you want many of them.

42

General Radio Discussion / Custom ferrites

« on: December 18, 2018, 1716 UTC »

Sorry for the tease subject, but I think I may be on to something.

First, something about me. In my other life, I am a potter. I dig up mud from the ground, shape it, glaze it, and make tableware.
I have a serious interest in the design and use of industrial furnaces and kilns, vacuum firing, special materials ETC.
That being said, it would not be too long a road to tool up to make custom ferrite cores, and with luck I could be able to produce repeatable results on call within a year or two. 

So, what I am looking for is interest. Is there an interest in the radio and hobby electronics community for custom ferrites?
any shapes, sizes, frequency ranges that are difficult to get or heinously expensive?
Does anyone need anything that is not commercialy available?

if interest exists, I may seriously consider setting up to make custom shapes in small batches. if not feel free to tell me I am just letting my mind wander and that there is no point.
                         Thanks ---EC

43

Equipment / Re: General Coverage Comms rxer down to 20KHz?

« on: December 18, 2018, 1705 UTC »

If you use an active antenna or antenna preamplifier the low sensitivity may not be a problem, many such receivers just have a 6dB/octave roloff below a certain frequency, or a transformer that is designed to be lossy at lower frequencies to prevent overloading from static or broadcasts. the performance and selectivity should not suffer as long as you can get enough signal into the receiver.

There are also modifications listed online for many rigs, and improving LF performance may be as simple as removing an RC circuit or winding a new transformer, I however, understand if you would want to modify n expensive new radio. not so sure I would either.

(I have this problem, where I modify things that work perfectly and break them, most of my repair skills came from repairing stuff I broke)

44

Longwave Loggings / Re: Northern California Winter NDB Logs

« on: December 15, 2018, 0723 UTC »

New Ones for tonight. I did not scan the entire band, but otherwise propagation seems better than normal.
IP 201 Mobile AZ  USA
BY 212 Beachy SK CAN
ZAB 215 Edmonton AB CAN
YD 230 Smithers BC CAN
BVS 240 Skagit Bay WA USA
TH 244 Thompson MB CAN
YZE 245 Gore Bay ON CAN
ZYC 254 Calgary AB CAN

These and some of the usual suspects. I guess staying up an hour later has its benefits.
As Usual, 1972 analog receiver, 150Hz crystal filter, and a passive T antenna

45

Longwave Loggings / Re: Northern California Winter NDB Logs

« on: December 14, 2018, 1832 UTC »

Short listening session last night, snagged some new ones
QV 385 Yorkton SK CAN
GW 371 Kuujjuaraapik QC CAN
and heard SB 397 San Bernardino CA USA for the first time in a while.
These along with many repeats.