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Low-Band VHF
A Neglected Resource
by Erik Bayer AF6EF
Low Band VHF.... A Neglected Resource
The public service radio systems are all trying to move off the frequencies from 30-50 Mhz and are crowding into high-band 150-170 Mhz with closer channel spacing. The reason is strong interference when ionospheric skip propagation brings another station 1000 miles away right on the same channel the local agency is using, ruining and confusing communications for both. However, we radio amateurs are not locked into specific channels, so we can move frequency and keep right on communicating.
The low band is much better at getting through forests and over mountain terrain than high band within about a 30 mile radius. Amateurs have also neglected this resource in their emcoms toolkit in favor of using more repeaters and more technology on line-of-sight frequencies. That requires placing relay stations on ridge tops or having repeaters/digipeaters available. 28 Mhz antennas are simple, and most all HF transceivers have 28 Mhz SSB. Many newer rigs have 10 MHz SSB capability.
In Butte County we need both line-of-sight and rough terrain communications ability. The public service agencies especially need our help deep in the canyons of the Feather River country. Did you know that 70 percent of Butte County land area is in mountainous terrain? Hams naturally think all we need is 80 and 40 meters in that situation, but think about it....you have to get a clear frequency and hold a clear frequency. Those bands are better suited for longer range of 100 or 200 miles than 25 miles. So, how best do we use the low VHF bands of 10 and 6 meters?
Much experimentation can be done using the new sound card digital modes that allow weak signals to cut through the noise on low band. Many hams already have radio equipment for 10 meters and 6 meters, but there is not much activity since we are in the low part of the sunspot cycle. Let's give it a go and see what can be done! Maybe compare with signals on 2 meter SSB digital modes from same remote locations and see which works the best.
Radios Available:
All the newer multi-band multi-modes by Kenwood, Yaesu, and Icom will work. For those on a low budget, get an RCI 2950dx or 2970dx for 10 meters, or a Uniden HR2510, or a Radio Shack 10 m rig. I have an Alinco DX70TH that I bought used for $425.00 on E-Bay which has 6 meters on it. If you plan to use any 6 or 10 meter repeaters get a 100 watt output on FM as you would have to be line of sight with the repeater to use low power. Ten-Tec has an all-mode VHF rig called the 6N2 with 20 watt output on 6 and 2 meter bands.
Sound Card Interface:
- West Mountain Radio Rigblaster (www.westmountainradio.com) available through AES
- MFJ available through AES
- Tigertronics (www.tigertronics.com)
- Tigertronics has USB sound built in the interface, which solves Linux sound problems with some laptops.
Practical Antennas for Local Work:
Although the DXers all use horizontal antennas, local communication should be done with verticals. That way we can use simple whips on mobiles instead of halos or other cumbersome structures. Also, a low vertical puts out a good ground wave, which is what we want.
- Base station antenna should be rugged, weatherproof, a DC grounded design, which is safer, and low reception noise. A beam facing the mountains would be desirable.
- Mobile whips for 10 meters can be a good CB antenna shortened for 28 Mhz. Use one with a large, efficient loading coil or use a full quarter-wave.
- Mobile whips for 6 meters: If you have a coil type 2 meter 5/8 wave, like a Larson, it will work fine on 6 meters as a loaded quarter-wave without any cutting.
- Half-wave vertical j-pole www.cebik.com
- Commercial vertical, 1/2 wave or 5/8 wave
- 3 element vertical yagi (Put the gamma match bar up; maybe that will reduce interaction with the mast.)
- Vertical Quad
-
Cushcraft AR-10, AR-6 Ringo Vertical available from AES, R and L Electronics, HRO http://www.cushcraft.com
-
MACO Vertical available from R and L Electronics http://www.majestic-comm.com/profile.htm
-
Half-wave j-pole that breaks down in sections
-
Half-square wire antenna with tails 8 ft off the ground
-
Moxon Rectangle beam...vertical of course.
- Bruce array vertical curtain
- Elongated wire quad loop
Remember your challenge is quiet reception. So, if you use an open-ended antenna, put a 100mh RF choke across it on 10 meters so noise is shorted before it gets to your radio.
Mode Resources
SSB:
- 10 Meter frequencies 28.3-28.4 MHz, if too busy, general class 28.6-28.675 MHz.
- 6 Meter frequencies 50.2-50.6
- FM: Local Repeaters
- KC6USM Magalia 51.940 - 114.8 Tone
- N0EDS Clear Lake 51.960 - 114.8 Tone
- WD6AXM Grass Valley 52.600 -151.4 Tone
- PSK,MFSK: (narrow band modes)
- 28.070-28.120, 50.290, 50.350-50.375
Software:
Windows
- Digipan www.digipan.net
- NBEMS www.w1hkj.com (download macros for NBEMS)
- IZ8BLY Stream http://xoomer.alice.it/aporcino/Stream/index.htm
Linux
- Fldigi (Digipup live CD) www.w1hkj.com
- gmfsk (In Ubuntu 5.10 and above)
SSTV:
Frequencies
- 28.677,680,683 is legal in all SSB portion of band.
- 50.680, 50.3-50.6 all mode portion
Packet:
Frequencies
- 28.110? see www.n0ary.org
- 50.6-50.8 20 Khz channels except 50.680 SSTV
Software:
- AGW Packet,AGW Term www.elcom.gr/sv2agw
Challenges We Face
Skip Interference
When the band opens up we can QSY to a less busy portion and avoid the DX windows for local operation.
Local noise
Power line noise is a big limitation on reception. Try to locate sources of local noise, and if they can't be eliminated, try to site the antenna to avoid the noise. More on that in antennas.
Solar noise
Events on the sun make a frying noise similar to power line noise; it is worst when the gain pattern of the antenna is facing the sun, least when sun is down or directly overhead on a half wave vertical antenna. We can use a directional antenna facing away from the sun and toward our desired station, turn up the power, or go to a narrow band mode to punch through. Local operations will not be assuming a clear channel at all times, and when stations are on standby to pass traffic, periodic checks will have to be made to maintain communications when working in weak signal conditions.
Preparing For Action:
Sound card interfaces, everyone have and learn the same software, learn your radio, practice in the field so we know what will work from various locations. Get nearby groups in on the project... Chico, Yuba-Sutter, Plumas. Set up rugged antennas at base stations that will be there in case of need, and have practice sessions that involve the new technician licensees.