Tactical Repeater Experience?

[radioguy]

For some time now, our tactical repeater performance seems to be much less, coverage/range-wise, than others in our Wing.  According to what we're told, we should be getting much more practical performance than we're seeing, but we can't point to any particular problem.  All the obvious items have been checked... correct DC power, repeater RF output, duplexer condition, aircraft antenna, etc.

In order to better confirm what we've been led to believe is "normal", I'd appreciate the input of a larger audience, especially those with significant tactical repeater experience. What type of range should we be expecting?
 
...from a typical HIGHBIRD altitude to a base station(ie Mission Base)? 
...from a typical HIGHBIRD altitude to other ground stations (mobiles, handhelds)? 
...from a typical HIGHBIRD altitude to other aircraft at 1500-2000' AGL? 

Can anyone think of any known issues or "hidden" items that might be escaping our technical evaluations?

Any information could be helpful.  Thanks.

[tmgoethe]

A line of sight calculator should get you close on range. There is one here:

https://www.southwestantennas.com/calculator/line-of-sight

The connectors and coax often get damaged and sometimes antennas are as well. I would try to find someone to check the SWR on the AC antennas and verify that all is well in that regard. Putting a meter on the repeater like a Bird would give you power output and SWR.

[radioguy]

Hello tmgoethe,

Been there; Done that.

All the usual suspects have been checked... some more than once. The only parameter that I can't confirm is the actual receiver sensitivity of the PDR, although the repeater has been checked by a commercial shop not too long ago. 

The LOS calculators that I have checked suggest air-to-air ranges approaching 200 miles and air-to-ground station ranges around 100 miles.  We're seeing far, far less.

I was hoping to get some responses from other tactical repeater/HIGHBIRD users reporting actual results, but your suggestions are appreciated.  Thanks.

[JayCraswell]

Do you know what altitude your highbird was flying at? At 10,000 ft I did some experimenting using an HT from the back seat and was talking simplex to stations all over the place (Some in a different state) and they all had great signals.  One of my customers of rehabbed 5300s talked from Alabama to the international space station when I was hearing it over Minnesota and well out to sea. I've got an MP4 from him that is pretty cool.

[radioguy]

This question still remains, so I'm bumping this thread to see if I can get any more input on this subject.  Thanks in advance.

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For some time now, our tactical repeater performance seems to be much less, coverage/range-wise, than others in our Wing.  According to what we're told, we should be getting much more practical performance than we're seeing, but we can't point to any particular problem.  All the obvious items have been checked... correct DC power, repeater RF output, duplexer condition, aircraft antenna, etc.

In order to better confirm what we've been led to believe is "normal", I'd appreciate the input of a larger audience, especially those with significant tactical repeater experience. What type of range should we be expecting? 
 
...from a typical HIGHBIRD altitude to a base station(ie Mission Base)?
...from a typical HIGHBIRD altitude to other ground stations (mobiles, handhelds)?
...from a typical HIGHBIRD altitude to lower aircraft at 1500-2000' AGL?

Can anyone think of any known issues or "hidden" items that might be escaping our technical evaluations?

Any information could be helpful.  Thanks.

[Fubar]

Wow, given all the troubleshooting you've done, it's hard to imagine there's anything else to try. When you say it's not performing as people think it should, what kind of performance are you getting?

One idea is to swap repeaters with another aircraft and see if there is a noticeable difference for either aircraft. It could help narrow down if the focus should be on the aircraft or the repeater itself.

[Craswell]

Bench testing is all well and good but I think switching the repeater off and getting some signal reports from ground stations from the Air Craft radio (Or a handheld in the back) versus the repeater will give you the answer you really need.  If there is radio chatter from the Aircraft on Aviation band (or the FM on a different channel) it will swamp the repeaters input so that would be one thing to insure is not the problem.  The line of site calculator is very accurate. I don't know the numbers off my head but the ISS (Space Station) is a couple hundred miles up (If directly overhead) and Alabama to Minnesota?? I'll have to get the MP4 of the CAP member using a member owned 5300 Mobile to talk to one of the astronauts.  Clear as a bell btw. VHF does a pretty great job for anything line of sight. Have you checked the SWR of the Aircraft's repeater antenna?  Is there maybe a damaged coax cable or loose connector or (The antenna Rod fell off) 

[radioguy]

Thanks for all of the comments thus far.  As to the SWR of the repeater antenna on the aircraft, the measured SWR (with an analyzer) was slightly above 2:1, as I recall.  After checking the specs for the antenna, however, the SWR design criteria is listed as 3:1 or better. 

In the time since my most recent post, we've had the opportunity to fly the repeater in another aircraft and the results were essentially the same.  At this point, about the only thing left to check is the actual measured sensitivity of the receiver in the repeater, both direct and through the duplexer.  However, this will likely require professional equipment and expertise (read: money!), so it may or may not happen.

[arajca]

You don't mention whether you reported it to the NTC or if you entered a case in CEMS. Have you?

[Craswell]

If the front end got too much overload from the Aircrafts FM it may have blown the preamp stage so I think your checking it out with a signal generator is an excellent next step. See if your wing has a Wing Engineer and maybe ask the Comm officer if they have someone who does radio repair for work (Or is a very talented amateur) I'm willing to be someone in your wing could give it a quick test for how sensitive it is and report back. If you have TA (Talk Around) set up on one of your radios you could bring that up with you and plug into the repeater antenna for some signal reports then switch over the the portapeater and see if there is any significant change. You may have already answered this but what altitude is your high bird flying at? One experiment not maybe of super great value but could give you a good idea of practical range without having to have a bunch of ground stations but get ahold of the repeater directory for your state and see how many you can reach from say 10,000 ft.  It should be quite a few.  *You may need to look at nearby wings to test this experiment as your range should be considerable. If you need a copy of the directory send me your email (And CAP ID please so I know your actually in CAP) and I'll send you my latest and greatest.  *Also looking for some input in my practical guide to radio and feedback on my universal code plug.  Hope you get it fixed!  Best Regards (505)333-9301 refurbatron@gmx.com

[Craswell]

I ran the previously mentioned line of site / useful range calculator and the results I got were a radius of 122 - 141 Miles.
Or in other words your in the center of a ring of stations that can go through your high bird that is 244 - 282 Miles.  *Assuming your doing figure 8s at 10k ft.  If your just loafing along at 1000 AGL your radius is 38-44 miles and your flying inside a practical ring of 76 to 88 miles.  *Which is not bad.  One ponders the fact that power off state wide only a few high birds could give one unbreakable channel (As long as their are runways and fuel and mobile or portable radios on battery or generator)  Some of these advanced trunking systems are maybe a bit too complex and I often wonder if during a "really bad day" we could provide communications for our Police/Fire folks that would work when all the ultra modern gizmos get overloaded or some major part of it gets damaged.  Maybe a mission worth talking about?  In my area trunking locked up when too many people turned their radios on all at once in a mass casualty event.  *Not even all talking.  Just too many on at once on one group *Note all second hand so I don't know for sure but considering what happened in Oakland/SF quake when everyone tried to make a cell call at once? They don't design these things for 100% users using them at once.  *Maybe they do now but I highly doubt it.

[radioguy]

You don't mention whether you reported it to the NTC or if you entered a case in CEMS. Have you?

NTC has seen this tactical repeater two times (or maybe three) in years past.  Currently, they list it as "Not Supported", just like many of our older assets.

[radioguy]

One experiment not maybe of super great value but could give you a good idea of practical range without having to have a bunch of ground stations but get ahold of the repeater directory for your state and see how many you can reach from say 10,000 ft.

Not a bad suggestion, but remember that this is a tactical repeater - and repeaters can't talk to repeaters.  In addition, this particular model is a single-channel / 10-watt-only configuration.

You may have already answered this but what altitude is your high bird flying at?

We typically fly our highbird at 6-9,000 ft., depending.

[Craswell]

6 to 9k should give you a huge repeater footprint. I was asked in an email about the difference between FM (or more accurately NBFM) versus P25 because I said P25 was better. Forgetting line of site airborne repeaters but say ground to ground communications where signals are degraded and bounced around the first time I had this shown was we had a Net Control trying to use a Mag Mount Mobile Antenna on his bathtub.  We were on FM and catching words here and there and even with cans (Headphones) on I couldn't pick up what the NCS was saying.  Our former Wing Commander informed us that we were all to go to the repeater on its P25 channel and I admit I scoffed at this suggestion.  Digital is always worse then analog right? Well... If the Digital Signal was just a pure block of audio data I think it probably would be worse but the people who created the P25 format made room for a lot of ECC data.  Error correcting code. I knew of this from the early computer days where we had 12 Drams for 8 bits (which would only need 8 Drams) The idea was that if any single bit of the 8 was "bad" the ECC controller using the extra 4 bits would correct the memory.  It was quite a demo to take a plyers and pull a ram chip from each row and have the machine run perfectly. And so with P25 and its ECC data you can take a useless FM signal and end up with a P25 Voice channel that is mostly "perfect"  Digital Audio always sounding more real. Like in the room real.  Sure a block would sometimes have so many errors in one section that ECC could not fix it but I believe P25 Forward Error Correction can handle some blocks that are pretty close to being perfect and still have some audio.  Kudos to whoever took this idea and applied it to radio.

One case where we were tasked with search for a man who had threatened suicide and all our operations were on FM. The local Sheriff took me aside to tell me that the local news (AM Radio?) guys were clearly listening to us and making up some incorrect assumptions / conclusions that didn't help matters. He knew enough about our equipment to suggest we change channels *Unannounced over the air.  And we only use P25. FM scanners tuned to P25 (I had to check this myself) sounds pretty much like radio static. Now P25 scanners were not as popular then but as the sheriff told me without knowing the frequency it was hard to zero in on what frequency we were on listening to FM.  And as I think everyone knows we can only do encryption with P25 so for a really secure connection that is the way to go.

Does anyone remember (or did anyone else have) check phrases for things like (Don't laugh) "The eagle has landed" if we had a Save.  There were some other ones like naming channels Charlie Uno for CC1

Back to the repeater in the aircraft I typically only use low power if there is a highbird to make the batteries last a little longer.  And in the VAN 50 Watts?  Yikes you can have perfect reception using FM with the space station (I will find that MP4 its pretty cool)

[Fubar]

Does anyone remember (or did anyone else have) check phrases for things like (Don't laugh) "The eagle has landed" if we had a Save.  There were some other ones like naming channels Charlie Uno for CC1

Perhaps this wasn't the rule when you were involved in that search, but to make sure members today understand using code words is no longer allowed:

1.6.1. Code Words, Codes, and Ciphers. Locally-created CAP codes, code words, and ciphers are not authorized (see 2.12.10). In the past it was a practice within CAP to assign "code words" to various mission events, such as "target found" in the belief that doing so would conceal these events from an undesired listener. This practice violates long-standing DOD policy and is seldom effective.