Radio setup for SAR

Discussion in 'Ham Radio Discussions' started by KM4SPU, Nov 9, 2018.

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  1. N3PM

    N3PM Ham Member QRZ Page

    The word "relay" is key here. Sometimes it's a real person relaying. Especially necessary if interoperability is problem.
    How are your incidents managed? Is freelancing allowed? Just curious.
    Mike N3PM
     
  2. W0PV

    W0PV Ham Member QRZ Page

    Ouch!

    Well at least you got to see how much big difference having a less loaded less lossy antenna can do for your signal needs.

    The fail on a tubing telescope whip mounted in that manner was of course quite predictable. Better to keep one of those around tucked away for backup if needed during more stationary ops.

    A non-collapsible full sized flexible whip made from Nitinol (see links in previous post) would be fixed frequency band but still hi-performance electrically and relatively indestructible if a bit more awkward to move around with or store.

    Good luck!
     
    Last edited: Feb 10, 2019
  3. KY5U

    KY5U Subscriber QRZ Page

    When I was a fire officer in charge, a set up like this worked. I clipped it to my fire coat high up so I could talk without removing it.

    F28B558A-5642-47DE-8635-5F02C1378B4A.jpeg
     
  4. W0PV

    W0PV Ham Member QRZ Page

    Mike, I am not sure what you mean by "freelancing" in this context. Please advise.

    I am not formally involved with SAR or ARES here at the moment. I am just an observer and offer help when it seems to be needed. Does that make me a "freelancer"?

    If so, then yes, freelancing does not seem to be rejected here, at least by the ARES or other ham groups. They take my checkin's and offers for relays, phone calls, or other services on an ad hoc basis, even when they are working together with other Public Service agencies, USCG, CAP, etc.

    73, John, WØPV
     
  5. N3PM

    N3PM Ham Member QRZ Page

    John, freelancing generally concerns team members or units that perform actions on their own without coordination from an incident commander. If an IC doesn't know where his teams or units are, or isn't updated on situation reports the whole focus shifts when units aren't accounted for. Sometimes a bonafide communications problem exists, sometimes not. I became used to 20 minute accountability checks with occasional "constant chatter" in more sensitive situations.
    Whether it's a 20 story building or 100 acres, personnnel accountability is most important. Everyone goes home at the end of the shift.
    Mike N3PM
     
    KY5U and W0PV like this.
  6. KM4SPU

    KM4SPU Ham Member QRZ Page

    Accountability is definitely key.
    • The first thing we do is sign in and the last thing we do is sign out. The Search Management Coordinator is always the last person to leave and makes sure everyone is accounted for. If you forget to sign out, they will try to reach you by cell. If that is unsuccessful, they will dispatch a police officer to do a wellness check on you.
    • In the interim, we have a dispatcher who keeps track of you in transit. You text them when you leave home, arrive at base, leave base, and get back home. If you've had a long day or a long drive, sometimes they check on you mid-travel or talk to you on the way home if its really late at night. They will make sure, you aren't too tired and will suggest sleeping before going home when applicable.
    • During the mission the radio operator keeps both a comm log and a team accountability log. Each time you call in an accountability check (usually every 60 minutes), or any other significant radio call, they will update your location on the form. If enough personnel exist at base, someone will also update your location on the master map (zoom in to see the details).
    • We have experimented with devices that passively track your position but base need internet for this to work. The state has a cache of them but I have only seen us use them in training.
    • In order to respond, or for that matter, be asked to respond by VDEM, you need to belong to a group who has a MOU with the state. To my knowledge, there are no groups who specialize in comms although there are certainly a few people people that know more the average bear. There are a few people who when they respond, tend to operate the radio a lot, but those few are by no means comms experts. Once in a blue moon I have seen either a mobile repeater in someone's truck positioned or relay person staged somewhere, but that is RARE. Task saturation is typically high so the incident would have to be pretty large for comms resources to deploy as many searches are resolved in the first few hours. Self dispatching is not allowed and will typically be turned away, although in a handful of situations, we have used emergent volunteers.
     
    KY5U likes this.
  7. N3PM

    N3PM Ham Member QRZ Page

    OK. Since you and your teams can be accounted for, task and location, then the loss of, or need for more communication is relatively small. As N5PAR suggested, cross banding on ham freqs is probably the simplest. This would require someone at the CP to be able to use both service's radios. Our system had an IC's aide, who usually had three radios hanging on him. (fire ground, dispatch, and emergency channel) This may have changed by now, it's been a while.
    The need for a person as a relay may include a tunnel, sub basements, anywheres a handheld just won't make it. In your case a steep hill radio shadow could give you hard time. (our firegrounds and emergency channels were simplex, not trunking)
    It seems un-radiolike to use a middleman but, one presentation on ham radio emergency comms I attended went as far as considering a "runner" be appointed, if the radio circuits didn't work.
    These situations are great for brainstorm training, followed by a couple of drills. You'd may be surprised at what solutions come out of left field.
    Stay Safe
    Mike N3PM
     
    KY5U likes this.
  8. KM4SPU

    KM4SPU Ham Member QRZ Page

    I emailed the guy who makes the Nitinol antenna and he said that to get their antennas to be the right length for 155 MHz I should cut off 1" from the top of their antenna. Does the length of my coax pigtail affect this in any way?
     
  9. N1BCG

    N1BCG Ham Member QRZ Page

    Probably not, but more importantly, an exact antenna length requires the rest of the antenna to be precise. This is unlikely given that the counterpoise (for what it’s worth) is the pigtail, the radio, an external mic cable, your arm if you hold it, and random coupling to your body and other metal objects.

    HT antennas are traditionally aweful, and more so with lower frequencies.

    Also, be careful cutting the end off a telescoping antenna. Eye injury potential...
     
  10. W0PV

    W0PV Ham Member QRZ Page

    Probably not too much.

    But there is a way to isolate and minimize the pigtail effect while also probably enhancing the antenna performance. Modify the typical 1/4 wave whip into a 1/2 wave dipole configuration by adding a fixed length tuned second half element.

    This can be seen on the video for the SAR antenna in post #66 as the orange mounting stem which contains a conductor inside (the coax pigtail goes to the yellow center). Instead making a rigid enclosure for it you could instead just add a wire and let it hang down as described on this web site.

    The whip and the wire together make a 1/2 wave dipole, which is a balanced antenna, therefore less prone to feed line issues, and best gain for performance. Both sides of a dipole are electrically the same length.

    To validate the advice given to you for cutting the whip to tune it for SAR, be aware there is a mathematical formula to determine the length based on the commonly taught rule of thumb 468/ mHz = length in feet for a half wave antenna.

    So for each 1/4 wave length half section, whip or wire, in inches, that algebraically transforms to 2808 / mHz = inches.

    If the whip is originally cut for 2 meter amateur band, or about 145 mHz, that would be 2808 / 145 = 19.37" To modify it for SAR band as requested, that's 2808 / 155 = 18.17", or 19.37 - 18.17 = about 1.25" shorter.

    But first verify how long the supplied whip actually is before cutting. Measure it. The point being the absolute length calculated for SAR should be 18.17"

    Of course in practice the best way to verify element(s) length plus feed line and mounting effects is by measuring the RF performance while transmitting. This is commonly done with an antenna analyzer or just a SWR bridge instrument workable at VHF frequencies. Most any ham club will have people that would be equipped and happy to assist you with that task.

    Be precise, at those frequencies a fraction of an inch does matter. If you make a "trailing wire" dipole, that wire element should be a length equal to the whip or for SAR 18.17". The trailing wire has the advantage of being more easily varied, trimmed or lengthened, if measurement indicates that fine tuning is desired. Slight asymmetries in length to obtain best measured results are OK.
     

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