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NCPACKET: Repeater sites

While putting nodes at great sites is perfectly reasonable, whoever is promoting that idea might want to have a pretty complete understanding of what is involved. Many repeater sites are not particularly happy with adding several transceivers and antennas, and will initially balk at the idea. Furthermore, they won't be really happy with frequent visits to get the system working.

Not everything about a TARPN network at a repeater site is bad news, once we have a great grip on what equipment is required. All of the radios can be simplex and can be protected with a pass cavity filter. Repeater sites love cavity filters. The radios we can use will almost always be commercial land-mobile surplus 2-way radios which also have great repeater-site credability. Considering that each radio only has to talk to one other station, the antennas can each be a small directional or small dipole antenna. The radios can be on less used spectrum, on different bands than the other customers, or perhaps 10s of megahertz away from other customers. TARPNs don't need to be on 2meters, especially at good sites.

Some of the antennas can be low on a hill-top repeater tower, possibly not on the tower at all. For instance, some of the link partners may be in line-of-site of the bottom of the tower. Pick your link partners well. Maybe one hill out to the south-west, one hill out to the east, another to the north, and then two stations within a couple of miles of the site?

If you are going to try to get a node placed at a repeater site, try to pick a site which allows direct and unsupervised ham access, i.e. a ham site, and try to be an expert at building and operating TARPN nodes before you go further than tendering the subject. You definitely do NOT want to request access, to start installing, before building and installing a few hamshack class node sites, with similar radios and path-losses involved, and acheiving retry rates under 3% sustained. You will also want to build your repeater site with at least 3 links, preferably 4 or 5. Consider 220mhz, 425mhz, and 900mhz radios because these are on less-popular spectrum at a typical repeater site.

Some repeater sites are ok with auxiliary masts and even having a separately secured radio cabinet outside the owner's security fence.

Repeater sites don't like coax with wire shielding because this creates an unnecessarily high noise floor due to close proximity to multiple on-the-air transmitters. You'll want to use Heliax.

Repeater sites, as a rule, will not tollerate frequency agility. Proposed frequencies are run through an application which hunts out potential mixing products between other transmitters which are close by. Mixing products would jam receivers at the site, potentially resulting in service disruption, leading to loss of business. You'll have to expose the frequencies used and wait for the site owner to get back to you. Choose wisely because changing things without permission, for other than justifiable chaotic life and death emergency purposes, will put your equipment out on the street.

Maybe the first rule for putting packet radio at a repeater site is to attract somebody to the local packet community who already has equipment at desirable sites. Make sure anybody who advocates for you has a pretty solid understanding of the reasons for dedicated links and exclusively ham-radio linking.

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