THanks for the Google Reference Phil.  My design is based on the Military designs of teh MK-2551 and MK-2900 portable grounding system which has been tested repeatedly by the military for static, High Discharge and lightning ground resistance on many different soil conditions.  One of those reports which relied on is attached here:

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA277285

Being mobile and not knowing what soil conditions I am going to come across, results will of course vary, and it is better to err on the side of safety as we mentioned above, but this is the best easy install and extract system I could find at the time.  Blue Sky masts uses this design in their portable mast grounding systems. Is it perfect, no, far from it. You seem very knowledgeable in this area and I would welcome hearing any other design suggestions you might be aware of which are portable and effective.

Phil, How would I measure that resistance?  Would copper cables rather than stainless improve it?  Or are suggesting I have to go  deeper?  Deep is a problem obviously since this is protable and has to be installed reasonably quickly and taken out reasonable quickly.

Phil, Even with that ground, we still shut down radio ops if storms are very nearby, even if we have teams in the field. We try to stay on the air until all teams are in or under cover, but sometimes we just have to shut down radio ops with a final message to the teams and come back when the storm passes.  I don't totally trust the lightning ground setup I use but it does give me a bit of security as we are calling the teams back in.

Lee

WB6BYU, Thanks for the reply.  How far I am willing to go depends on two things, Money and Portability/ease of setup and take down. Transporting a full 4 or 6 pack of full size two meter cans will likely be over the top.  I am looking for something portable. I do not want to attenuate too much, because we typically operate in the woods and signals are already low power and often faint for APRS. Any suggestions which meet these needs?

Phil, I will read the article.  Thanks.  As for grounding, I described it quickly above but basically it is a fairly expedient lightning ground I learned about in an Army Field Antenna Manual. The coax from the antenna, comes down to Copper Plate in a NEMA box with and ICE arrester mounted on it. The plate is attached to two 2" copper straps running down to a stainless saddle clamp at the base of the mast (about 18"). From there, four one quarter inch Stainless Steel rope cables run for 25 in four equal directions. These cables lay on the ground (bare ground if possible). Each of these cables are bonded with bronze bonding clamps to 5 equally spaced 18" copper clad ground rods spaced 5 feet apart along each cable. That makes 360" inches of ground rods spread over 100ft of cable.  I have never tested it with real lightning but I put my faith in the US Army I guess.  Does it sound adequate?

Thanks Phil.  I do not think they are tunable.  They are 2Mhz wide and look to be pre-tuned to 145Mhz.  My frequency for APRS is 144.390Mhz  If I don't transmit vhf on the top antenna below 146Mhz, this should be OK. I will keep looking for a tunable one, however. IS 100db some sort of goal.  I can only find one at this price so I was thinking 50db would be good.

As for grounding, I do not always ground it.  However I do frequently.  We live and work in Central Florida.  We have a great deal of lightning and I have witnessed some pretty unusual lightning behavior here.  Clear sky above,Clouds only on the distant horizon, and lightning bolt hit a palm tree outside my house and took out some electronics in the house,  Many others.  So if there is any chance of lightning in the greater area of operation that day, I ground it.

Phil,  Will This sort of band pass filter do the trick?  I think I can get one for $100.

http://www.dci.ca/pdf/DCI-145-2H.pdf

N4CR, Great Info for me to consider. Using RG-214 for the APRS antenna is no problem and probably a very good idea. I will have to further into Bans Pass filters. Perhaps there are some designs out there to build a small unit which will suffice. Or , if I am lucky I might find something in the used market.  If I bought another mast, it is my understanding that the antenna would have to be located potentially hundreds of feet apart. Any idea what a reasonable distance apart might be if the receiver is listening on 144.390 and the transmitter is roughly 147Mhz?

Getting another mast is certainly cheaper than many options, if I can have them located within a reasonable distance of our Command post.  I guess I am being a bit lazy by not wanting to have to erect, guy, and ground two masts, each time we setup, and then break it all down again.  However, I might just be lazy enough to choose and electrically engineered solution, rather than a mechanical one.

Tisha, Thank you again for the reply. The x50A is a collinear as you describe. Since the Antenna which will be place on the mast beneath it will only be a receive only antenna, is the radiation pattern of the second antenna even an issue?  You are right about the concerns of the mast in the field.  Wind will be factor.  The mast is a simple 3" aluminum sectional mast. Wind will likely spin the pvc arm to a downwind position, but since each section spins fairly freely, only restricted by the friction of the connecting joins the corkscrew into the ground is not a concern.  The mast also sits on 12 inch pad to prevent ground peneration. However I think I can guy the arm to maintain a down wind position.  The second antenna will be a collinear vertical as well but a shorter one, an X30a. It should have a fairly low wind cross section.  

If no one else has additional advice I will try this configuration and see what kind of results I achieve. I will report back when I have completed this.

Lee

Very clearly explained!!  Thank you!  I can certainly try ferrite beads.  I can also try to offset from the mast by Putting the two antennas on PVC Arms.  How far from the mast would they have to be? When ti comes to vertical stacking, do the two antennas have to be DIRECTLY above each other (each on the same length arm) or can the one on top be directly on the top of the mast and the one on the bottom (receive only) of the stack be offset by maybe 18-24 inches.  Offsetting both to the same side of the mast may cause come pinching in the Mast raising mechanism but I think I can work around it with helpers on the guys lines while raising and lowering.

Lee

Thanks for the reply. IF there is little risk of damaging the APRS Receiver on 144.390 then I am going to simply try the APRS Receive only antenna 15-20' below the Dual Band Transceiver antenna at the top of the mast (45'). A missed packet here and there will likely not make a difference.  Can you explain a bit more about how one goes about achieving "good decoupling of the coax and Mast"?  Does it require High Q filters, shielded cable of some kind?  special grounding. The mast is grounded well per military specs on most sites it is used. The Coax is Belden 9913 run through a IEC lightning arrestor which is grounded to the Milspec Grounding array.  The grounding is 4 quarter inch stainless steel cables, 25' long each, laid on the ground level, each with 5, equally spaced, 15-18" deep copper clad grounding rods, bonded with Bronze clamps.

Lee

Thanks for the repsonse. I wouldn't even know where to begin with NEC modeling. Any suggestions on an easy way to do this without learning all the electrical engineering to populate such programs. As for Common Mode Isolation of feedlines and Mast. how is this best achieved.  I did say I was a total amateur about antenna theory and the tools required.

Lee

Thanks for replying, Tisha. What you describe in your 4th paragraph, so much more clearly than I did, is what  I hope to accomplish. The  Diamond X50a is a vertically polarized dual band antenna. I was considering a similar antenna for the Receive Only APRS antenna (though maybe not as big and not dual band).  I was planing on mounting it as you describe, but 20' below the top antenna. Since the APRS receive only Antenna will only be on 144.390 Mhz, and the Crossband antenna will be on 146 +- Mhz and 444+- Mhz my question is, how much interference or intermod could I expect and how could I filter/compensate for that?

Also, which antenna would be better placed on top.  The Crossband, or the APRS Receive only antenna? I am leaning toward the Crossband.

Lee
 

I manage comms for a regional Search and Rescue group.  Being a highly trained but All volunteer organization, comms can be quite challenging  given the LOW budgets we have to work with.  I currently run  a 40FT portable tower with  Diamond X50s at the top.  This antenna services simplex or crossband voice. I feed a Kenwood TM-D710A. Typically, we run simplex on one side of the radio (either UHF or VHF) and I run APRS receive on the other.  We track our Teams live using APRS.  

Recently, we have found more and more applications for Crossband, and thus both sides of the 710a are being used and I can't track APRS. Thus I have added an old TD7a as an APRS receiver-only to connect to the PC tracking software.  

My question is antenna config.  Are there any devices which would allow me to continue to use just the one X50 Antenna to feed the receive of both radios, AND still transmit on either band?  My Guess is no.  Thus I am considering a second, receive only antenna for the APRS receive.  The real question is can I mount both antennas on the same mast and not get too much interference?  I know that is very much frequency based.  We typically use UHF simplex for voice, or crossband UHF and VHF simplex. Thus Typically transmit is only UHF.  My thinking is that I leave the X50 on the top of the mast at roughly 45' on center, and then mount the receive APRS ONLY (144.390) at 20 Ft on a 24 inch arm offset from the mast.  Is this sufficient separation to not blow out the APRS Receiver?  I typically transmit at 15 Watts, but have gone to 50 watts in some areas.  

OK I am a rank amateur in antenna theory so please be kind.  Any help would be appreciated?

Lee
KJ4KLM

Wouldn't the same shock risk be there in the gator cases when mounting the radios to the shelves in the case?  I would think so unless you want to purchase the military grade rack mount cases with shock mounts. Those are much larger and heavier and much more expensive.  Also, when considering the gator cases, their footprint on the table is just as large or larger than the Pelican 1550.

 I am in the later stages of an almost identical project to the original poster and am wrestling with many of the same mounting issues.  I am using the identical radios you are using, TS-480SAT and a TM-D710A. I have a Samlex 1235, RigRunner, PwrGuard, Super PwrGate, all under the custom cut panel. The panel is custom cut to move all the radio ports to the surface so they are accessible for paddle, computer hookup, Antenna hookup, headphones, Microphones, and for bridging the two radio for cross band between HF and V/Uhf.  As for the head I have designed a cavity and 16x 4 opening in the panel. There is an aluminum plate which covers this opening and screws on with thumbscrews at each end.  The radio heads are mounted on this panel. For storage this panel comes off and I flip over the panel and mount it over the opening with the heads down inside the case, and secured with the thumb screws. For operation I flip the panel  the other way up and screw it down with the same thumb screws and have the heads right there at the front of of the case. I have surplus gas springs to hold the lid up at a 90 degree angle and keep it from flopping down on the heads and damaging them.  I have a magnetic white board mounted on the top for notes, tracking teams,  with a Powerwerx LED light for night operation mounted above it. I have a dual time clock mounted in the upper right hand corner of the whiteboard.  For the cooling issue, I have two 12v fans, One blowing into the cavity beneath the panel, and one drawing out. The air inside is exchanged about once every 4 seconds. The temperature is monitored/displayed and the fans are controlled by a digital controller from Coolerguys.com.

I have purchased and dry fitted most all the components except the panel and am trying to decide how to mount the hardware to the bottom of the case.  The fit is quite tight and to allow airflow I need to keep certain stacked components with space above and below.  Thus there is really no clearance left for any shock padding on the bottom of the case.  This does concern me a bit when it comes to shock protection.  I would love to see pictures of your ultimate solution and layout under the panel.

So VE2DC,  I am passable with a soldering iron, but have no knowledge of the parts etc, I am no electrical engineer, and have no real testing equipment other than a good multi meter. If  you think that qualifies me to attempt this I am game to try.  I can't really wreck this much further and if I do, it was free. 

First, I really don't know what parts to replace.  I have downloaded the Service manual on this radio and (as you would expect) there was no part labeled "VHF Final" .  So can you or anyone tell me what parts I am looking for?  KA5IPF said the part was $46.  Thus I assume he must know what "The Part" is I need to try to fix this?  Someone else suggested that some of the other parts feeding "the final" might be bad which may have led to the the final being blown.  What are these parts which might have led to this and how do I test them?

Any elmers have some help on these questions before I jump into trying to fix it myself?

Lee