Help with a HAM Operator and regulations

I just received this email from a HAM operator in our county. It appears he has actually gone out and located most of our towers. He knows much more than I do about radio, which he has attemted to demostrate here, and the FCC rules. Before I respond to him, I need some input from you guys! Sorry, but its a little long…


Any news on the new fiber backbone? Other than some late night dropouts and some slow downs, it’s been doing pretty good lately. Knock on wood?

Also wanted to touch base with you on another topic. Are your wireless AP’s Motorola Canopy? I know you’re using 900 MHz part 15 gear, but not sure who made it.

Reason I ask is 902-928 MHz is a ham radio band. Hams are licensed users, secondary to US Govt and Part 18 licensed users. The hams MAINLY use the following two areas of the band:

#1 - 902-903.2 MHz - horizontally polarized, fixed stations using very directional links with very high ERP’s (kilowatt plus is common).

#2 - 927-928 MHz - usually vertically polarized, both mobile and fixed stations. Hams are using this region more and more for FM voice and digital data links. Transmit powers is usually in the 5-30 watt range to omni antennas of various gain figures.3 digit ERP levels are pretty common.

Local area ham radio usage of the 927-928 region is set to increase considerably this fall and up into next year as a local ham radio FSK data network is deployed at sites near Dry Ridge, Williamstown, Jonesville, and Owenton. FM voice usage of this region is also increasing. Obviously there is some potential there for harmful interference to/from your WISP operations and thus why I wanted to touch base with you on this topic.

If you have Canopy AP’s operating with a channel center at or above 924 MHz (one of the defaults for Canopy ?) interference is likely. If you could adjust that channel center down to 923 should keep the frequency hopping out of the 927-928 region and prevent most interference issues. I think this change can even be done remotely?

I haven’t checked the Jonesville tower, but I do hear strong frequency hopping signals in the 927 region from the Stewartsville, Dry Ridge, Sipple Road and Humes Ridge towers. These are the towers most likely to cause or suffer interference problems from nearby ham radio operations in the 927 MHz region. The Hilltop site could be another problem site, but I haven’t checked any further. With the high power 929 MHz paging stations around Dry Ridge and Williamstown, moving those down 1 MHz might also help the receiver front ends on your AP’s.

Regarding the 902-903 region of the band? AP’s with a channel center of 906 MHz or below could easily see interference. The interference would likely be very intermittent. Since very high transmit ERPs and horizontally polarized ham radio signals are involved, the interference to the AP could be severe.
Adjustment of 906 MHz channel centers up to 907 MHz would be an option for your system.

With both of these channel center adjustments (906 to 907 and 924 to 923) in place, you should still have 3 full bandwidth, non-overlapping channels for each tower site. I think all your sites have 3 AP’s in place, so this should work out fine for your system.

I think working together, both the local ham radio operations and the City’s WISP operations can coexist with minimal or no harmful interference issues.
I’d be glad to meet or talk with you regarding any questions or help you may need on this matter.

Jeff Thomas
(ham callsign WA4ZKO)

HAM Operators are licensed users of the band. Another blunder by the FCC to allow unlicensed use of the band as well as licensed HAM.

Fortunately you have a guy who seems very willing to work with you and I would encourage you to be diplomatic. As a licensed operator he gets priority. He is asking you make a little room at the top and bottom of the band which is not unreasonable.

I would do some testing by turning off AP’s and having him check for interference. If he is seeing FHSS, it may be someone else or he maybe mistaking the GPS sync transmission signature of the Canopy for FHSS. It’s a good idea to be sure before re-arranging the network.

If it is you, you may also be able to do some channel re-assignments so that your 915 channels are pointing at his transmitters and your 906 and 924 channels are pointing away.

I dont know if youve ever talked to a hammie up close and personal, these guys live for rf. Theyll make an antenna out of a spool of thread coated in solder, and tied to a pocan and wrapped around a dog bone, and talk to a guy in china and the folks up running on the colbert treadmill on the international space station. If youre not super RF savvy, you will walk away fromt he conversation wondering how the hell you are dealing in RF with such little knowledge.

Theyre also a testy lot, so definely maintain a friendly diplomatic relation, or if they chose to they could hose your noise floor (though they wont cause most of them have a true respect for RF in general, in their life order of importamce is God, Flag, RF, Family). If hes a subscriber, I wouldnt recomend offering up too much info on your network. Also dont give in to his request immediately, or else you run a high risk of him feeling he has some ownership of your network, and next thing you know hes showing up at your office with the new layout for your network.

That being said, the man has some pretty good points, working together with competing frequency users is better than working against, as the latter will most always end in a lose lose situation, and cost alot of money. But take into account, exery time you make a concession, that takes away one option you have in the event of other issues arising.

I would like to point something out about Canopy: Center frequencies of 907 and 915 ARE overlapping. The same for 915 and 923. You only have three non overlapping frequencies if you use 906, 915, and 924. No other combination works.

This is exactly why I never deploy 3x 120deg or 6x60 sectors. For full 360 degree coverage I use either 1x 360 omni or 4x 90deg sectors only using two frequencies. This allows for coordination with other operators and only uses 1 or 2 channels. If what he says will be occuring in your area I would prepare to move to one of these configurations if you have not already.

I would also like to mention that in my area HAMs use the center 914-917 for Video transmissions. I believe they can use up to 50 Watts or more for these systems. I would suggest using a 4x 90 system with center channels of 908 and 922. This would allow you to avoid all HAM frequencies.

- Matt

mattmann72 wrote:
I would also like to mention that in my area HAMs use the center 914-917 for Video transmissions. I believe they can use up to 50 Watts or more for these systems.

Actually, under Part 97 rules, we're allowed to operate with up to 1500W PEP into the antenna, with certain geographic exceptions here in the US. This is why I'm not running any 900MHz canopy anywhere in my systems, because my amateur operations will drastically interfere with same. :)

On completely separate note, I've got an extremely loud spurious signal being generated by the 5.2SM on my tower, right at 144.150MHz. I have confirmed this by powering down the unit. It is definitely much louder than 40dB lower than the primary carrier signal, and thus in violation of FCC emission limits under its type acceptance. What's the best way about fighting this battle with Motorola?

That sounds like the Ethernet. Are you using shielded cable?

jwcn wrote:
That sounds like the Ethernet. Are you using shielded cable?

Yes, shielded cable. The ethernet signal runs at 100MHz, so that's not it. It's interesting that the interference is not present when the radio first powers up, but only becomes noticeable once the SM links up with the AP. I have been able to confirm this by powering down the AP for a period of time. Thus, it appears to be a spur only when the unit is linked. RF mixer problem, maybe?