Thursday, November 19, 2009

Medium Wave Trans-Pacific DX

   Here is a Youtube video I made of station JOUB 774Khz, 500KW, Akita, Japan being received at my QTH in King Salmon, Ca. This was recorded at around 3:00AM, and the signal was Q-5, very good copy for a Medium Wave radio station 4775 mi. away. The program is an English lesson on the educational NHK-2 network.

   Note that other Asian stations are being received, although much weaker. Their frequencies are offset from the domestic stations due to the 9Khz channel spacing used in Asia. Some of the stations are too close to domestic signals to be copied, although strong hetrodynes can be heard.

   JOUB on 774Khz is the strongest of the Asian super power stations at 500KW. It's frequency makes it easy to copy through the heavy QRM  from the "local" stations. This is the first frequency to try for TPDX.

Here is a list of Asian super power stations in order of your chances of receiving them:

1) JOUB-774 Akita, Japan (500 KW) This northern-Japan powerhouse broadcasts the national NHK2 network program, and is the most frequently reported first TP in North America. Parallel to 693 and 828

2) JOIB-747 Sapporo, Japan (500 KW) Depending on your local QRM situation, this booming station can be a better bet than JOUB. Carries the national NHK1 program with many foreign language lessons, // 594.

3) JOBB-828 Osaka, Japan (300 KW) Usually makes an appearance when the above two show up, but southern Japan location can have different propagation. NHK 2 program parallel to 693 and 774

4) JOAK-594 Tokyo, Japan (300 KW) Not in the same league as the big three, but can be surprisingly strong during propagation peaks. NHK1 program parallel to JOIB-747

5) JOAB-693 Tokyo, Japan (500 KW) Doesn’t have the booming signal of the above, but easy to log when propagation is right. One of the more challenging Japanese stations.

6) HLCA-972 Dangjin, S. Korea (1500 KW) Has different propagation than Japan, and can really boom in when peaks favor Korea. Somewhat more seasonal than Japan, September and October are best

7) HLAZ-1566 Jeju, S. Korea (250 KW) Commonly used to check upper-band TP propagation, this religious broadcaster can boom in when upper band is strong. Carries Japanese-language religious programs frequently

8) VOA-1575 Ban Rasom, Thailand (1000 KW) Probably the most distant common TP, this station typically carries news programs in SE Asia languages. Very seasonal, with propagation best around equinox periods

9) JOIK-567 Sapporo, Japan (100 KW) The chances of logging this one are slim to none (unless you are right on the ocean shore)

I have seen the carriers from all the stations on the list. They can be seen on the spectrum display long before they can be heard. This is HLAZ-1566 Jeju, S. Korea (250 KW). VOA-1575 Ban Rasom, Thailand (1000 KW) can also be seen. 
   Also note the digital "HD" carrier on the 1550 signal. The FCC is very obviously paid off or completely stupid to allow this to happen to the AM band. Unbelieveable... if you caused this much QRM on 75 meters you would be getting death threats... Not only does the digital carrier trash adjacent trashes its own analog signal. I don't get it... there is NO guard band, it bumps up right against the adjacent channel carrier. Click photo for better view.

Monday, November 16, 2009

Bench testing power tubes

Here I am testing a pair of 4-65A's that I bought off ebay. One was good, one the vacuum leaked out, or the air leaked in depending on your point of view. Below is the good one running at full 65 watt input, 650V @100ma. I like this picture so much I am going to use it as the title picture for my blog.

Here is a shot of the test setup. The Heathkit power supply is for screen and bias. The plate supply is to the left and can supply up to 1KV, controlled by the variac. This same setup was used to thest the big RCA 7213 shown further down this blog.

Here is the bad one. The filament was about half brighteness due to air in the tube conducting the heat away. Unfortunately it burned out before I could get a good shot of it. The milky look is smoke inside the tube. (Click the picture for a larger view.) You can see it swirling around near the bottom of the plate.

All glass power tubes without a flashed getter are prone to gas when not used for long periods of time. In this type tube the plate is the getter. High temperature operation of the Tantalum plate cleans up any gas
in the tube by chemical reaction. It is important to rotate your spares to keep them cleaned up and gas free.

Thursday, November 12, 2009

HF propagation prediction tools

The Austrailian government has a REALLY nice set of free Web based HF prediction tools. Check them out at: IPS Radio and Space Services. Below is a screen capture of an HAP (Hourly Area Prediction) plot that shows the usable frequencies centered on N. California. This plot covers 4-9PM (UTC -8 time zone). It shows what we already know, 75 is good in the early evening. After 5PM 75 "goes long" and 160 is the place to be. Note that at 8PM even 160 goes long and there is no short skip at all.

Monday, November 9, 2009

Collins 30S-1 (SK) Almost

The Collins 30S-1 amp I acquired from Mac, W6FCS bit the dust a while back. It always had an intermittent problem with dropping off line. At first it seemed that it was a control logic problem. Finally one day it happened... an arcing sound, blown fuses, and a terrific smell. The power transformer was arcing to ground. I tried putting the transformer on a board to lift it above ground. It worked... on the CW position. It was still a no go in the SSB position though. New transformers are available from what used to be Peter Dahl... for $650 plus shipping. Not a happening deal anytime soon. It occured to me that a pair of HV transformers I had bought off ebay might just work. They fit, and the voltage with the secondaries in series was just right. So I set about installing them and a new bridge rectifier in the space occupied by the old transformer and tube sockets.

Here is a shot of my son Isaac who was a big help on the project. Isaac did most of the wiring, and we had a good time together working on the amp.

Here is a shot of the new transformers and rectifiers. I reused as many of the original parts as possible, including the terminals and end insulators from the wires. I used the inner conductor from RG-8 as the new HV wires. The rectifiers are from the old channel 6 analog transmitter.

I had to add a seperate screen transformer. A 120 to 240 isolation transformer from the old channel 6 transmitter was perfect for this application.

Here it is ready for testing. The HP meter says it outputs just about 1KW, all it was designed to do. The HV is exactly 3000 just as it originally was, along with 200V on the screen.

The camera flash makes it look like it's on... it's not. I only had the HV up with the cover on.

Well surfs up, so I need to go put on my wet suit and wax my board.

The waves were really beautiful this weekend here in King Salmon.

Wednesday, November 4, 2009

Don't try this trick at home

Here I am testing a couple of RCA 7213 power tetrodes. These are 1500W plate dissapation tubes which will give 1350W output at 1200Mhz, CCS. They are speced for SSB linear service. The Heathkit supply is for screen and bias. The variac and transformer provides plate HV. This was an emission test conducted at 750V. The tubes had better than 1A of emission which is the max plate current per the spec sheet.

Here is a close up of the tube and socket. The socket came from a CH 6 analog TV transmitter that I had the extreme pleasure to help dismantle. This socket was from the visual driver stage which used a similar tube, the 8792 which is impossible to find used and cost about 8K new. The 7213 seems to be common and cheap as it was used in airport navagation systems. The two I have were $10 on ebay for both. They are both good and matched almost exactly although they were made about 8 years apart.

It took about 4 hours to clean and polish the socket and to cut new mylar bypass rings. This socket is setup for grounded grid with bypass rings on both grids. This is the screen ring, the control grid ring is underneath and looks identical complete with the .01 caps. The  mylar rings are cut from 3 mil sheet which has an insulation rating of 21KV! I don't believe it could do that in a real world situation, but I know it takes 1500V no problem. Anyway look to hear this on the air someday.

A Plumbers delight receiving loop for 75 Meters

Here is another shielded loop antenna I built to help with the grow house noise on 75 meters. I call this type of construction "plumbers delight" becaue it is built entirely from the plumbing department of your local hardware store. It works a little better than the shielded loopstick described below. Being outdoors it gets a better signal and is farther away from AC wiring and noise sources in your house. It is fixed tuned for the AM window and basically impossible to retune without opening up the box. It is now sealed with silicone and is still clamped in the vise. The nulls are very sharp and can greatly reduce noise coming from a fixed source.

It is constructed from 1/2" aluminum tubing a couple of compression fittings and a brass T. One of the compression fittins is for 5/8" tubing. A short piece of plastic tubing is slipped over the aluminum tubing to insulate it. The loop is one turn of #14 wire 2.5' in dia.

Here is a close up of the insulated end. A plastic ferrule would be better but they are hard to find here behind the Redwood Curtain.

The T is supported by a copper sweat fitting that has been silver soldered to a brass plate and screwed to the top of a cast box.

The loop is tuned with about 400pf  and matched to 50 ohms by two 4:1 broadband RF transformers cascaded for a 16:1 impedance ratio. These are mounted inside the box.

This antenna for most will be easier to build than the shielded loopstick. It has a much lower output due to no preamp, but my old NC-303 has plenty of gain so it really does not matter. As long as you can hear noise when the antenna is connected, thats all the gain you need.