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AMRAD Active Whip Antenna

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Chris Russell

Thu Aug 02 2007, 03:12AM

... not Russel!
Registered Member #1 Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052

Hi all,

I just finished building a slighly modified version of the AMRAD active whip, and all I can say is wow. If anyone is looking for a good solid receive antenna, this is it.

Sensitivity is good down to 10kHz. My location is a bit noisy, but I can still make out the big VLF transmitters in Maine, North Dakota, Hawaii, Puerto Rico, the UK, France, and Italy. I'm sure SAQ will come in nicely on this antenna, so I am keeping my eyes peeled for announcements about upcoming transmissions. I haven't seen the Alpha stations yet, but that could be due to noise issues, or they may not be transmitting at all.

Sensitivity is great all the way up to 30MHz or so. I copied WWVH on 5MHz with no problem. I haven't given the HF end a really good workout yet, though, as I am working on some RFI issues.

For NDB DXing, you really can't beat it. For those who don't know, NDBs are non-directional beacons that operate from 200-500kHz or so, used for aeronautical navigation. The relatively low-powered stations transmit a morse code ID, and they're on 24/7, which makes them fun and challenging to listen for. Good code practice, too! At any rate, even though my location is fairly noisy, I did surprisingly well. With my loop antenna, I was lucky to pick out three or four beacons a night. Here is a list of the beacons I was able to copy with the whip over two nights, as well as their distance from me, in miles.

First night:
ML 230
NA 487
F8 180
RJ 305
YXK 250
YMW 365
SC 158
BUP 36
LNT 54
YY 258
BV 185
YLD 731 <-- not bad!
YFM 650
BH 33
FC 124
YPP 352
YLQ 263
BST 35
OLD 8 <-- no records broken there
YTF 287
UL 255
BG 11
BX 694
LRG 33

Second night, skipping previously heard beacons:
ZV 386
CLB 891 <-- powerful beacon in SC, easily copied most places, except here LRG is right on top of it
YKQ 649
DF 605
SB 602
MT 436
VO 483
YSK 923 <-- longest distance so far
YXR 564
UM 631
YUY 539
Y8 193
QI 146

If anyone is thinking of building this antenna, I can vouch for it. This is just an insane improvement over every other antenna I've ever used for VLF/LF/MF. If there's any interest, I can post pictures of the construction, as well as recordings/screencaps of various signals heard with the antenna.

Dave Marshall

Thu Aug 02 2007, 03:21AM

Registered Member #16 Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554

I'm definitely interested in all of the above. If its that effective I might just build a loaded vertical for 100Hz-10Khz and do an active whip for everything else.

Dave

Chris Russell

Thu Aug 02 2007, 03:35AM

... not Russel!
Registered Member #1 Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052

I think, in the interest of being organized, I'll start a project thread for it tomorrow, and keep the discussion about it here.

The only thing keeping it from working quite as well as it could all the way down to 0hz is the transformer. Adding more turns would get you down into the right frequency range, but it would send the otherwise astoundingly excellent HF/MF intermod performance right to hell. That would be a shame, because it's really great. In fact, the intermod performance of the antenna greatly exceeds the intermod performance of the FT-857's receiver.

Maybe some sort of relay could be used to switch back and forth from two different transformers.

I've attached the QST article detailing the active whip below.
]1186025702_1_FT29318_0109031.pdf[/file]

ShawnLG

Thu Aug 02 2007, 03:54AM

Registered Member #286 Joined: Mon Mar 06 2006, 04:52AM
Location:
Posts: 399

Nice Chris! I had tried to track NDB in the past with a home build longwave radio. I need to try this antenna out myself. By the way, have you pick up any LowFER beacons with your antenna?

My old NDB list:
388 khz NXX Willow Grove, PA,
363 Khz RNB Millville, NJ, 50W
336 Khz PV Atlantic city airport, NJ
254 Khz CAT Chatham, NJ
216 Khz CLB Carolina Beach Wilmington, NC, 400W
208 Khz UKT Pennridge airport OR Quakertown, PA
198 Khz DIW Dixon, NC, 2000W

Chris Russell

Thu Aug 02 2007, 04:27AM

... not Russel!
Registered Member #1 Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052

Wow, you just reminded me, I scrawled one more in the margins after wandering down where I didn't expect to see any beacons: DIW 849. Good to see there's some overlap in addition to CLB!

I'm going to try for lowfer beacons soon. Mostly I just wanted to confirm that the antenna was working properly, and that the batteries would power the circuit without any issues (I didn't build the 24V power supply, as I wanted the antenna to be portable, so it runs off of two 5AH lead acid batteries in series). Now that I'm confident that I can run the antenna overnight, I'll give the lowfers a shot.

I should note though that I did copy WD2XSH/17 from Marshfield, MA, on the new 505khz experimental band. Not too bad!

Dave Marshall

Thu Aug 02 2007, 05:25AM

Registered Member #16 Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554

Very interesting. I've got a 6' telescoping whip, and a bunch of 4' steel whips and ferrules from my now retired hamsticks that I can use. I'll have to order the parts when I get home.

So that entire chunk of copper pipe is the heatsink for the CP-666? Seems like since you have to run a power supply lead up to the thing anyway, a much more reasonable sink with a small fan might be more suitable. If the CP-666 does get that hot, Georgia summers that average heat indexes of 105F would probably be rough on it.

On a semi-related note: Shawn, why the heck aren't you a ham? You need to get licensed!

dAVE

Chris Russell

Thu Aug 02 2007, 06:39AM

... not Russel!
Registered Member #1 Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052

The CP666 doesn't get all that hot. If you look at the schematic and the adjustment instructions, you'll see that when in operation, 24V is applied, 53mA of current flows. That's 5.3V across the 100 ohm resistor, and 18.7V across the CP666, thus causing a dissipation of about a watt. In my case, I am supplying more like 27V (dropping slowly to about 24V) to the CP666, so my dissipation is a tad higher. A standard TO-5 heatsink can dissipate a watt, but it will rise something like 80C over ambient. The CP666 is rated to 200C (linear and tough, at least you get what you pay for), so it could probably handle it just fine... but when you're shelling out $14 for a JFET, you might as well make sure it's going to last a lifetime.

Even the author of the article admits the copper pipe is a bit extreme:

Note that off-the-shelf TO-5 heat sinks can't handle the heat as they are too lightweight. I had to go to a home brew heat sink to get the delta T (temperature rise) down where I wanted it especially inside the PVC pipe. This thing will work in the middle of Saudi Arabia now.

For my design, I put a TO-5 heatsink on the transistor, then clamped a TO-220 heatsink on top of the whole thing. Total temperature rise above ambient is minor, maybe 1-2 degrees C, with 1.18W dissipation. If you're going with the PVC pipe, might as well follow the design they've supplied, as it's known to work in all environments. My enclosure is a bit roomier, and though I probably could put a fan in, it's jut not needed. I was also worried that a fan might generate noise, either by capacitively coupling noise to the gate of the JFET, or by introducing noise into the power supply.

Oh, and you don't run a power supply lead to it. The power is supplied through the coax. Keeps it simple.

For the whip itself, I am using one of the many whips I got with my hamstick with the antenna. It measures just an inch shy of four feet (about 1.2 meters). I don't think going any longer than that would be of much help, as the limiting factor for LF seems to be atmospheric noise. However, if you wanted to improve VLF response, using a wider whip would increase the input capacitance of the antenna. The telescoping whip would be a neat idea; you could shorten the whip quickly if a strong signal was causing overload.

Chris Russell

Mon Aug 06 2007, 02:11AM

... not Russel!
Registered Member #1 Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052

Just a quick addition, here's a recording I made at about 0155UTC on 189khz. The source is a longwave broadcast station in Iceland. Not too bad!
]1186366276_1_FT29318_pianoman-189khz.mp3[/file]

ShawnLG

Tue Nov 17 2009, 08:59PM

Registered Member #286 Joined: Mon Mar 06 2006, 04:52AM
Location:
Posts: 399

Last night, I have picked up 26 NDBs. I only used 20ft of wire connected to a Kenwood TS-430S which is then feed through a PC running Spectran.

216khz CLB Carolina Beach, NC USA 15db
272khz YQA Muskoka, ON, Canada 10db
278khz NM Matagami, QC Canada 15db
326khz FC Fredericton NB, Canada 10db
329khz YHN Hornepayne, ON Canada 10db
332khz YFM La Grande-4 QC Canada 15db
335khz YLD Chapleau, ON Canada 18db
340khz YY MONT-JOLI, QC CANADA 20db
341khz YYU Kapuskasing, ON Canda 10db
344khz JA Jacksonville, FL USA 7db
360khz PN Port Menier, QC Canada 20db
362khz SB Sudbury, ON Canada 15db
363khz RNB Millville, NJ USA 20db
366khz YMW Maniwaki QC, Canada 20db
369khz TT Trenton, NJ USA
377khz YRR Ottawa-Freely, ON Canada 10db
378khz RJ Roberval, QC Canada 10db
382khz LQ Boston, MA USA 10db
390khz JT Stephenville, NL Canada 10db
391khz DDP San Juan, PR Puerto Rico 20db
392khz ML Monroe, LA USA 15db
407khz ZHU Montreal, QC Canada 10db
415khz CBC Cayman Brac, Cayman Islands 7db
419khz RYS Detroit, MI USA 5db
516khz YWA Petawawa, ON canada 15db
520khz F9 Miramichi, NB Canada 16db

Proud Mary

Tue Nov 17 2009, 09:45PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Hi Chris,

the best distance I ever got in non-amateur service was between my sledge station GVPZ on the pack ice north of Nordauslandet, Svalbard, Norway, straight across the North Pole to sledge station GRFA on Elleslere Island, Canada.

My xmitter was a Racal Syncal 1W LP, 4W HP SSB manpack, operating in the Intermediate Frequency (2MHz - 2.5MHz) band by courtesy of the Norwegian Ministry of Justice and the Sysselmann pÃ¥ Svalbard (roughly, the Governor-Generalship) of Svalbard.

The antenna was a 6m whip with guy ropes fixed to the top of an iceberg, and the earth submerged directly into the sea at the foot of the berg (a very very dangerous place!!!!)

This was better than 1000 miles per watt, since the deep-frozen NiCd batteries were unable to produce enough power on "High Power" (4W) so the traffic took place with 1W RT LSB. Curiously, I could barely hear Svalbard Radio in Longyearbyen, only a few hundred miles away across mountains, ice-caps, and glaciers) but I guess we were half way across the skip distance.

I guess that if conditions had deteriorated, we could have got even further on W/T, because the 1W from my end was perfectly intelligible at Ranulph Fiennes' end in Canada.

We stayed in contact nightlly for about ten days as we made our way round Nordaustlandet (The North-East Land) a great glaciated island to the North East of Spitsbergen, when one day the communications just stopped. The sky waves had turned against us,
but it was the most exciting radio contact I have ever had.

Nordauslandet is a mysterious place, grave-yard of hundreds of ships since walrus and whaling times, graveyard of the Balloonist Andre, and of Roald Amundsen himself, the fittest place for him to vanish beyond Antarctica. In summer, where the beach is free of ice,
you can see the skulls and crosses of Russian trappers of hundreds of years ago, ships' spars from the 19th century, logs floated free from Siberia, fragments of lost ships, all kinds of ammunition and explosives, and Nazi weather stations from World War II.

It is written up with photos of polar bears &c in Short Wave Magazine of August 1989, when I lived my life as a man, and I will always be happy to send a copy of the article and pictures to anyone who is interested in the HF elements of the history of the Minotaur,

Stella X

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