HF Antenna For EMA Tower

csimpson911

Member
Joined
Dec 25, 2014
Messages
6
Location
East Central Mississippi
I'm assisting with designs for a new emergency management building that will have a 150' tower on-site. We are looking to place a HF antenna on the tower and want it to cover the 20, 40 & 80m bands. I need some advice for an antenna to be placed on the tower that has very high wind resistance. The communications company that is designing the tower needs to know what type of HF antenna we will be placing on the tower so they can get the specs on the tower to us. Currently I am only licensed as a technician, studying to take my general this year....so I'm not proficient in HF antennas. Thanks for any help.
 

prcguy

Member
Joined
Jun 30, 2006
Messages
9,873
Location
So Cal - Richardson, TX - Tewksbury, MA
For state, county, city emergency management stuff you usually want regional comms on 40 and 80m, like within a 500mi circle. 20m is usually used as a DX band to access other parts of the country and you need an antenna that will do both things well.

With that a horizontal wire antenna is the antenna of choice using NVIS on 40 and 80m but it will also work ok DX on those bands. An ideal height would be horizontal roughly 32-35ft off the ground. This is the best compromise for 40 and 80m NVIS, plus its the first half wavelength up for 20m giving you a low angle takeoff for DX. You can choose a center fed dipole that covers those bands, or an 80m offset center fed dipole (OCFD) or a resonant end fed halfwave with an 80m low end cut off. All of these antennas are around 133ft long.

You can attach any of these to the tower at the proper height but you will need at least one other attachment point close to the same height with the end fed being the easiest and the OCFD being the second easiest and a center fed usually needs three attachment points to be secure in high winds.

If you are considering a vertical, you will loose comms out of ground wave range, or you will have a dead zone from about 50mi to several hundred miles and that's not good for an EMCOM antenna. A Yagi or directional is not very practical for 80m but a good idea for 20m. If the organization has two HF radios you could use a horizontal wire for 40/80 to one radio then a vertical that covers 20m or a small Yagi that covers 20m to the other radio for simultaneous operation.

For OCFD or resonant EFHW antennas, the best I know of are made by MyAntennas. I have many of them and you take them out of the box, hang them up and operate, no tuner needed. The model EFW-7510-2K is a newer model end fed that is modified to cover the 75m voice band or roughly 3.8 to 4.0MHz plus all other bands to 10m and usually with no tuner. The OFC-8010E-3K is the offset center fed version but its tuned more in the 3.6MHz range of 80m but there is a simple mod to change that to 3.8-4.0MHz.
 
Last edited:

csimpson911

Member
Joined
Dec 25, 2014
Messages
6
Location
East Central Mississippi
For state, county, city emergency management stuff you usually want regional comms on 40 and 80m, like within a 500mi circle. 20m is usually used as a DX band to access other parts of the country and you need an antenna that will do both things well.

With that a horizontal wire antenna is the antenna of choice using NVIS on 40 and 80m but it will also work ok DX on those bands. An ideal height would be horizontal roughly 32-35ft off the ground. This is the best compromise for 40 and 80m NVIS, plus its the first half wavelength up for 20m giving you a low angle takeoff for DX. You can choose a center fed dipole that covers those bands, or an 80m offset center fed dipole (OCFD) or a resonant end fed halfwave with an 80m low end cut off. All of these antennas are around 133ft long.

You can attach any of these to the tower at the proper height but you will need at least one other attachment point close to the same height with the end fed being the easiest and the OCFD being the second easiest and a center fed usually needs three attachment points to be secure in high winds.

If you are considering a vertical, you will loose comms out of ground wave range, or you will have a dead zone from about 50mi to several hundred miles and that's not good for an EMCOM antenna. A Yagi or directional is not very practical for 80m but a good idea for 20m. If the organization has two HF radios you could use a horizontal wire for 40/80 to one radio then a vertical that covers 20m or a small Yagi that covers 20m to the other radio for simultaneous operation.

For OCFD or resonant EFHW antennas, the best I know of are made by MyAntennas. I have many of them and you take them out of the box, hang them up and operate, no tuner needed. The model EFW-7510-2K is a newer model end fed that is modified to cover the 75m voice band or roughly 3.8 to 4.0MHz plus all other bands to 10m and usually with no tuner. The OFC-8010E-3K is the offset center fed version but its tuned more in the 3.6MHz range of 80m but there is a simple mod to change that to 3.8-4.0MHz.
Not what I was hoping to hear, but I definitely appreciate the information.
 

prcguy

Member
Joined
Jun 30, 2006
Messages
9,873
Location
So Cal - Richardson, TX - Tewksbury, MA
Every type of antenna has it purpose and sometimes your needs don't fit what you might have pictured you needed. Will the tower be guyed? If so you could possibly have one of the lower guy cables be custom installed with insulators so it has a 133ft section that spans an area 25-35ft off the ground, then just buy a MyAntennas transformer used with their end feds and attach to the insulated section of guy cable.

If the tower is free standing it will easily handle the pull of a wire antenna that is attached around the 32-35ft level, but you would need an attachment point 133ft away. If you are willing to accept a lower level of performance you could go with a 9:1 type transformer and there are various lengths of wire that kind of work ok across many bands. I believe 73ft is one of those lengths and that's a lot easier to find an attachment point at the far end. You would need a tuner.

Other companies like Chameleon use a 5:1 transformer and they have models like the Emcom II with about 60ft of wire and they work ok on 40m but will be down some on 20m and down a lot on 80m, but they do make contacts and do require a tuner. I have a couple of Chameleon antennas (CHA MPAS 100 and 500w) and have measured the degradation compared to a EFHW and OCFD and have kept my EFHWs and OCFDs up permanently because I would rather not give up any level of performance.

Not what I was hoping to hear, but I definitely appreciate the information.
 

ko6jw_2

Member
Premium Subscriber
Joined
May 18, 2008
Messages
1,049
Location
Santa Ynez, CA
You should consider adding 60m capability. These five channels are used for interoperability between amateur radio, FEMA and the military. In the present circumstances of fires in the West, hurricanes in the East and Gulf and the COVID-19 situation Channel 1 5330.5MHz is the primary voice channel and Channel 2 5345.5 for digital traffic. Our experience suggests a horizontal antenna. Verticals do not seem to perform well on 60m. We have successfully conducted tests with FEMA and military stations. A ham license is not required for EOC personnel.
 

ka3jjz

Wiki Admin Emeritus
Joined
Jul 22, 2002
Messages
23,109
Location
Bowie, Md.
It's very important to emphasize that hams are secondary on those channels; Fed Gov is primary. Mike
 

vagrant

ker-muhj-uhn
Joined
Nov 19, 2005
Messages
1,577
Location
California
Would using an OCFD as an inverted V, or an End Fed at a slope work well enough? That obviously eliminates the need for another tower to keep the wire horizontal. There will be less TX/RX gain between the two, but some testing with a single tower is easy enough before moving forward with another tower. Even better would be two OCFD wires that are perpendicular to each other and connect to a switch to improve TX/RX in a particular direction.
 

prcguy

Member
Joined
Jun 30, 2006
Messages
9,873
Location
So Cal - Richardson, TX - Tewksbury, MA
They work fine as inverted V or sloping. The key is to get the region of highest radiation at the right height for the job and my opinion is that's about 1/4 wavelength high on 40m so its got the most gain straight up and its not too high for NVIS and its also a good compromise for 80m NVIS and 20m DX. If the antenna sloped where one end was 10-20ft off the ground and the other end was 40-50ft and the high current point was about 32ft on 40m its fine.

At low heights like this its almost omni directional on NVIS and a little directional on DX but not enough to worry about. On 20m it will have a lot of nulls and gain lobes and its a good idea to map out those lobes and orient the antenna during installation to make best use of them for DX.

Would using an OCFD as an inverted V, or an End Fed at a slope work well enough? That obviously eliminates the need for another tower to keep the wire horizontal. There will be less TX/RX gain between the two, but some testing with a single tower is easy enough before moving forward with another tower. Even better would be two OCFD wires that are perpendicular to each other and connect to a switch to improve TX/RX in a particular direction.
 

ko6jw_2

Member
Premium Subscriber
Joined
May 18, 2008
Messages
1,049
Location
Santa Ynez, CA
It's very important to emphasize that hams are secondary on those channels; Fed Gov is primary. Mike
Under normal circumstances that is true. The point is that FEMA wants to have ARES utilize these interoperability channels when needed. They have drills quarterly to test this use with ham radio operators. The drills have involved making contacts with military bases around the country. That's why an EOC needs to include 60m.
 

popnokick

Member
Premium Subscriber
Joined
Mar 21, 2004
Messages
2,073
Location
Northeast PA
The OCFD and End-Fed Halfwave wire antennas both work on 60M with a tuner (which you should have for either antenna anyway).
 

csimpson911

Member
Joined
Dec 25, 2014
Messages
6
Location
East Central Mississippi
Every type of antenna has it purpose and sometimes your needs don't fit what you might have pictured you needed. Will the tower be guyed? If so you could possibly have one of the lower guy cables be custom installed with insulators so it has a 133ft section that spans an area 25-35ft off the ground, then just buy a MyAntennas transformer used with their end feds and attach to the insulated section of guy cable.

If the tower is free standing it will easily handle the pull of a wire antenna that is attached around the 32-35ft level, but you would need an attachment point 133ft away. If you are willing to accept a lower level of performance you could go with a 9:1 type transformer and there are various lengths of wire that kind of work ok across many bands. I believe 73ft is one of those lengths and that's a lot easier to find an attachment point at the far end. You would need a tuner.

Other companies like Chameleon use a 5:1 transformer and they have models like the Emcom II with about 60ft of wire and they work ok on 40m but will be down some on 20m and down a lot on 80m, but they do make contacts and do require a tuner. I have a couple of Chameleon antennas (CHA MPAS 100 and 500w) and have measured the degradation compared to a EFHW and OCFD and have kept my EFHWs and OCFDs up permanently because I would rather not give up any level of performance.
The tower will be guyed. The alternate SWIC for the state is a good friend and has suggested a horizontal antenna (multi band). I had thought about an inverted V, but wasn't sure about how well it would work trying to talk with the state EOC. They are 50-60 miles, as a crow flies, from our location. Also, was planning to use it as alternate communications for out-of-state communications for our USAR task force.
 

tweiss3

Member
Premium Subscriber
Joined
Apr 24, 2020
Messages
104
Location
Ohio
I actually really like this idea, and I never would have thought about it before. I have a MyAntennas EFHW 80-10 (the 200W version), and cannot say enough good things about their products performance, even if its not as high as it should be. It works at about 1.5 SWR without a tuner on all the bands as advertised, and works even better with a tuner. The reception results speak for themselves, so its transformer works really well.

Every type of antenna has it purpose and sometimes your needs don't fit what you might have pictured you needed. Will the tower be guyed? If so you could possibly have one of the lower guy cables be custom installed with insulators so it has a 133ft section that spans an area 25-35ft off the ground, then just buy a MyAntennas transformer used with their end feds and attach to the insulated section of guy cable.

If the tower is free standing it will easily handle the pull of a wire antenna that is attached around the 32-35ft level, but you would need an attachment point 133ft away. If you are willing to accept a lower level of performance you could go with a 9:1 type transformer and there are various lengths of wire that kind of work ok across many bands. I believe 73ft is one of those lengths and that's a lot easier to find an attachment point at the far end. You would need a tuner.

Other companies like Chameleon use a 5:1 transformer and they have models like the Emcom II with about 60ft of wire and they work ok on 40m but will be down some on 20m and down a lot on 80m, but they do make contacts and do require a tuner. I have a couple of Chameleon antennas (CHA MPAS 100 and 500w) and have measured the degradation compared to a EFHW and OCFD and have kept my EFHWs and OCFDs up permanently because I would rather not give up any level of performance.
 

popnokick

Member
Premium Subscriber
Joined
Mar 21, 2004
Messages
2,073
Location
Northeast PA
... but wasn't sure about how well it would work trying to talk with the state EOC. They are 50-60 miles, as a crow flies, from our location.
50-60 miles will almost always be achievable on some band with any of the multi-band antennas described by prcguy.... even installed at lower heights. Reaching the EOC should be a non-issue, barring an HF comms blackout from a solar eruption (an infrequent event).
 

AK9R

Lead Wiki Manager
Super Moderator
Joined
Jul 18, 2004
Messages
6,423
Location
Central Indiana
75m SSB or data can work at those distances (50-60 miles), but it can also be a bit frustrating depending on the antennas at both ends and local noise levels.

For that distance, 2m FM simplex will work if the antennas have a clear path between them. A 4-element Yagi at 100 feet on your tower pointed at the EOC might work pretty well. 6m FM simplex might be even better.

I agree with the previous statements that the 75-80m band will be a good bet for statewide coverage. I've been in nets in Indiana where we had pretty good communications over the length of the state (270 miles) on 75m. Yes, MS is a bit longer north-south than IN. OTOH, 40m propagation can be variable and you may find that you can't hear stations in-state, but out-of-state stations are clear.
 

csimpson911

Member
Joined
Dec 25, 2014
Messages
6
Location
East Central Mississippi
75m SSB or data can work at those distances (50-60 miles), but it can also be a bit frustrating depending on the antennas at both ends and local noise levels.

For that distance, 2m FM simplex will work if the antennas have a clear path between them. A 4-element Yagi at 100 feet on your tower pointed at the EOC might work pretty well. 6m FM simplex might be even better.

I agree with the previous statements that the 75-80m band will be a good bet for statewide coverage. I've been in nets in Indiana where we had pretty good communications over the length of the state (270 miles) on 75m. Yes, MS is a bit longer north-south than IN. OTOH, 40m propagation can be variable and you may find that you can't hear stations in-state, but out-of-state stations are clear.
Roger that
 

popnokick

Member
Premium Subscriber
Joined
Mar 21, 2004
Messages
2,073
Location
Northeast PA
The keys to communicating from the EMA will be 1) versatile, multi-band antenna(s), and 2) versatile, multi-band, multimode radio(s). 80M-6M minimum, with ability to go VHF / UHF a plus. You will have a very high probability of reaching EOC (and beyond) likely on more than one band / mode.
 

csimpson911

Member
Joined
Dec 25, 2014
Messages
6
Location
East Central Mississippi
The keys to communicating from the EMA will be 1) versatile, multi-band antenna(s), and 2) versatile, multi-band, multimode radio(s). 80M-6M minimum, with ability to go VHF / UHF a plus. You will have a very high probability of reaching EOC (and beyond) likely on more than one band / mode.
Roger, I was thinking about getting a HF/VHF/UHF rig. I would like to have situational awareness during hurricanes, for our area, with the state EOC, for teams deployed and as a back up comm set up.
 

wa8pyr

Technischer Guru
Lead Database Admin
Joined
Sep 22, 2002
Messages
5,134
Location
Ohio
I'm assisting with designs for a new emergency management building that will have a 150' tower on-site. We are looking to place a HF antenna on the tower and want it to cover the 20, 40 & 80m bands. I need some advice for an antenna to be placed on the tower that has very high wind resistance. The communications company that is designing the tower needs to know what type of HF antenna we will be placing on the tower so they can get the specs on the tower to us. Currently I am only licensed as a technician, studying to take my general this year....so I'm not proficient in HF antennas. Thanks for any help.
At our EOC we use an 80-10 OCFD wire antenna good for up to 500w. Works just fine.

You could install it with the center insulator on the tower and the end insulators tied off to a couple of guys, or to a building, whatever is handy.

Ditto to the comments about wanting to keep an NVIS footprint, so you don't want it 100 feet up; 30 feet or so is plenty.
 
Top