Survivalism & Self Sufficiency Topics > The HAM Radio Board

2200 meters and 630 meters now open to amateurs in the USA

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backwoods_engineer:
I'll start by listening.  My transceiver has a general coverage receiver that covers 472-479 kHz also.  I plan to build a Beverage receive antenna first.  (Good thing I'm buying some land soon).  There are some guys that plan to start transmitting soon on FT8 and JT65.

I'll have to build a power downconverter so I go down from (for example) 5.472 MHz to 0.472 MHz.  They say antenna efficiencies for reasonable heights on 630m are terrible, around 2%.

LodeRunner:

--- Quote from: Alan Georges on September 16, 2017, 07:28:21 AM ---Coming to a shack near you, October 16th:
https://swling.com/blog/2017/09/fcc-opens-630220-meters-october-16-pre-registration-required/

I'm staying out of that funhouse, but will look in the windows from time to time to see :wtf: they cook up.  Maybe a hardware mod to transmit on these bands with an FT-817?

--- End quote ---

Chicken.  We have a lot of fun on the BB blog.

And you'd be surprised what can be done on 630M, even with modest antennas - i.e. a G5RV or a 160M inverted-L.
You've gotta wind a loading coil, of course, but that's not rocket science.  And there's a number of kits for exciters and amplifiers, if you're not ready to build from scratch.
One I can recommend is the QRPLabs U3S - it does WSPR, QRSS, and CW on any band from 2200M to 2M, and can be set up for multiple bands - up to 6 with the [optional] 6BPF relay board, or whatever your DIY inclinations are.  Power output is about 1/4 watt below 30Mhz (with 5 volts on the final).  It can produce more RF output with 12V on the final, even more with 12V and an additional FET in the output stage...up to about 2 watts - this makes it a good stand-alone beacon for HF WSPR and as a QRP/CW rig, but 1/4~1/2 watt is plenty to drive my amp with.

FWIW, antenna efficiency isn't as bad as you think on 475Khz.  For a typical 'flattop G5RV' plus  a loading coil with good Q (i.e.about 300 or higher) and a decent set of ground radials, you could get as high as 7% to 9% efficiency.  With a 160M inverted-L and good groundplane, you could get as high as 10% to 12% efficient.

At 10% antenna efficiency, you still only need about 35 watts out of the amp to be at [the maximum allowed] 5 watts EIRP. (remember, the "I" stands for Isotropic)
There are no contesters, there are no stations with 2KW amps and 8-element arrays, and there are no appliance operators on 475Khz, so its easy to have fun and experiment.  And you'll be amazed how far 1 to 5 watts EIRP goes at night.  US/Australia and US/Japan contacts have already been made.  US/Europe contacts happen every night using CW, JT9, and other modes.  There's already a lot of activity. 
Tune in and check it out - you might decide to give it a try after all.

I bought a QRPLabs U3S kit and built it so I could get on the air quickly.  The kit is awesome, and the customer service was excellent.  The base transmitter kit is just $49 -- I spent $76 because I bought LowPass filters for several bands, plus a GPS module so I'd have integrated timesync and gridsquare data for WSPR - no laptop needed, the internal micro-controller does it all. 
Disclaimer:  I hold no financial or other pecuniary interest in QRPLabs - I am just really impressed with their product.

I built my own power amp on an old chunk of heatsink from an ancient stereo amplifier - I used a pair of [cheap] IRF-840s and about $20 worth of Mix #77 ferite material - two FB-77-1024 "beads" for the output tranny, and an FT-140-77 for the DC input choke  (ordered both the FETs and Ferites, plus the resistors and sundries I didn't have in the junk box from Mouser).  For about $50 I built an amp that will give 90 watts out for just over 1 watt input.  So only about 300mW drive is required to get me to the 35~40 watts output I need...  drive control is as simple as varying the voltage on the final transistor of the U3S kit.  About 6.5 volts gets me to exactly 5W EIRP (based on measured field strength).

My coil is about 200 feet of 12ga.solid [house wire] wound to 75 turns on a 12" sono-tube cardboard former (for cement piers).  Wire and Sonotube both bought at Lowes-Depot several years ago when I first started experimenting with LF/MF - cost about $40 all together.  Some folks will build a 'variometer' to make the coil adjustable so they can trim the antenna tuning easily.  I just use coil taps and get 'close enough', my setup works just fine.  And it's much simpler without having to build a variometer.

I'm receiving on my HF rig - an IC-746Pro - with a separate receive antenna, which is just a 500-foot loop of wire [on the ground] going into a 4:1 BALUN, then coax to the rig.  Theres no resonating or tuning the receive antenna, and no preamp is needed - It just works (this Loop-on-Ground antenna is also awesome for 160, 40, and 30 meters).


So there you have it.  For about $150 you can get on 475Khz and have a bunch of fun, and probably work some DX in the process.

Cheers,
Loderunner

LodeRunner:

--- Quote from: backwoods_engineer on September 25, 2017, 08:47:37 PM ---I'll start by listening.  My transceiver has a general coverage receiver that covers 472-479 kHz also.  I plan to build a Beverage receive antenna first.  (Good thing I'm buying some land soon).  There are some guys that plan to start transmitting soon on FT8 and JT65.

I'll have to build a power downconverter so I go down from (for example) 5.472 MHz to 0.472 MHz.  They say antenna efficiencies for reasonable heights on 630m are terrible, around 2%.

--- End quote ---

Before trying a "beverage", which is rather directional if it's long enough (1/2 wavelength is bare minimum - which is just over a thousand feet at 630M) try a loop antenna.  Get a 500ft. roll of 16ga or 14ga THHN stranded wire and lay it out on the ground in a roughly rectangular shape, 100'X150', or as close as you can get to that.  Feed with a 4:1 current BALUN and you're in business.  This antenna is also good for lower HF - 160~40 meters.

backwoods_engineer:

--- Quote from: LodeRunner on November 04, 2017, 02:23:46 AM ---Before trying a "beverage", which is rather directional if it's long enough (1/2 wavelength is bare minimum - which is just over a thousand feet at 630M) try a loop antenna.  Get a 500ft. roll of 16ga or 14ga THHN stranded wire and lay it out on the ground in a roughly rectangular shape, 100'X150', or as close as you can get to that.  Feed with a 4:1 current BALUN and you're in business.  This antenna is also good for lower HF - 160~40 meters.

--- End quote ---

Thanks for the advice.  I've got plenty of room now that I have 16 acres, and lots of trees.  I  might just try a loop.

LodeRunner:

--- Quote from: backwoods_engineer on November 09, 2017, 09:30:36 AM ---Thanks for the advice.  I've got plenty of room now that I have 16 acres, and lots of trees.  I  might just try a loop.

--- End quote ---

NP.  I've done a lot of modeling and experimentation with RX antennas over the last few years, and one thing I've learned is that a loop, on or very near the ground, is an excellent aperiodic (non-resonant) receive antenna for signals arriving at moderate angles.  Such a loop tends to work best where the circumference of the loop is 0.2 to 1.75 wavelengths (using Fmhz/1005 = 1wl in feet).  There's a 'dead spot' right around 2wl that results from a loop that length preferring signals *very* much off it's edge (i.e. arrival angles below 5 degrees) which are seriously attenuated when the loop is on the ground, or very low to the ground (and what isn't "low" in terms of wl, at 630M, right?).

With a 500 foot loop, you get a best-sensitivity range of 400Khz to 3.5Mhz.  The "dead spot" centered at "2 wavelengths" is at the top edge of 75 meters (3950~4020Khz depending on height and soil characteristics).  If you find it necessary to move that "dead spot" out of your way for 75M, trim 10~16 feet off the length of the wire, and that will push the "dead spot" up to about 4100Khz - but try it at 500Ft. first... you'll probably do just fine.
It might sound unusual, but I can actually transmit on 160M with my 500-foot Loop-on-Ground and easily make NVIS contacts.  A similarly provisioned 250-foot loop made an excellent NVIS transmit antenna for 80/75 meters here.  (I eliminated the 250-foot loop to make room for the 500-foot version)

Oh, and congrats on buying your rural property... let the fun begin  ;P

Cheers
/LR

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