Building a Bucket Ham Repeater

by ALC

 

Like you, I’ve been reading about the problems Rourke has been having getting his homemade radio repeater working recently.  Owning only a single Baofeng I wasn’t able to do any testing to offer any advice.  I have been tinkering with my own repeater solution for the past month or so though, but you could say I cheated right from the start and bought a dual band handheld that already had a repeater function built-in.  Most of my tinkering with it has been in testing and building the supporting infrastructure around it to make it more reliable and useful in a SHTF situation.  My plan for deploying this was geared towards a bugout to the woods or to an off-grid BOL where you’d need a radio repeater that was simple to setup, easy to remove or relocate, and that didn’t require much maintenance to keep it functioning.  I tried to keep the cost to a bare minimum, and, where possible, to use items other survivalists might already have available.  Consider this just a working prototype, and one that would greatly benefit from some better packaging.  But while it may be one ugly dog, it can do some pretty neat tricks.

 

So what is it, you ask?  The “Bucket Repeater” is a battery powered cross-band VHF/UHF repeater in a weather proof enclosure that can operate unattended for a week or more, and be remotely activated or deactivated from miles away as needed.

 

OK, but what’s it good for, and why would I want to build one?  Potentially it has a number of uses, but two that might be the most desirable are to increase the operating range of your other radios, and/or to allow users with radios that don’t share a common frequency to still have two-way communication.

 

It’s important to note that this is a cross-band repeater, and different from conventional police/ham repeaters that many might be more familiar with.  Conventional repeaters have an input frequency and an output frequency, call them “A” and “B”.  Anything received on the “A” frequency is retransmitted on the “B” frequency, and the A and B frequencies are both in the same band (VHF or UHF, for example).  Cross-band repeaters are different.  Their “A” and “B” frequencies MUST be in different bands (one in the 136-174Mhz range and the other in the 400-480MHz range for our purposes here), and they can transmit on both bands.  Anything received on the A frequency is retransmitted on the B frequency, AND anything received on B is retransmitted on A as well.  In short, if a signal is received on one, it goes out the other.  Repeaters and cross-band repeaters each have their own benefits and limitations, just noting some of the differences so you can make sure this will do what you want it to.

how to bug in

 

So how do you build it?  Well here’s one method, starting with what you’ll need:

 

  • 5-6 gallon pail w/lid
  • 12V battery (any that will fit really, but batteries are heavy, and tree branches do bend and break.  I chose a “Group U1” lawn/garden type)
  • Paint (to paint the bucket), and save the paint can lid (see below).
  • Silicone caulk or glue
  • Slingshot (optional)
  • Rope and string (optional)

Total cost: about $200 if you buy everything new.

 

Hopefully the pictures below are self-explanatory.  As just a general overview, all I’ve done is drill a hole in the bucket for the antenna coax to fit through. Caulked the paint can lid to the bucket lid for the magnetic mount antenna to stick to.  Wired the power for the radio from the battery (using the 12v radio adapter and the battery clamp/cigarette lighter adapter).  Put the battery and the radio in the bucket, ran the antenna cable through the hole into the bucket, attached the antenna cable using the SMA to SO-239 adapter, snapped the bucket lid on tight, stuck the antenna on the paint can lid, and raised the bucket up a tree with the help of the slingshot and the string.

 

Here’s the pieces:

 

pic_1

 

They all store pretty nicely in the bucket (have to bend the antenna just a bit) with some room to spare:

 

pic_2

 

 

To help get the bucket as high as possible, shoot the nut with the string attached over a tree branch using the slingshot.  Then tie the other end of the string to the rope, and the other end of the rope to the bucket handle.  Ensure all the connections are snug and that everything in the bucket is positioned so it won’t come loose while the bucket is hoisted, or in heavy winds.  Make sure everything is working correctly while it’s still on the ground.  Then pull the string until the rope is over the branch and back down to you, and then pull the rope to hoist the bucket up.

 

pic_3

 

Usually it takes (me, anyway) a couple tries to get the string over the branch you want.  Sometimes the string gets tangled and needs to be cut, note the extra string from a failed attempt in the foreground of the pic below, so pack extra string and nuts.  Eventually though:

 

pic_4

 

A few notes and a couple thoughts about the PX-UV973, and cross-band repeater use in general.

 

1) A short review on the PX-UV973 first – The cross-band repeater function of the PX-UV973 is just that, one function available on the radio.  When the repeater is “OFF”, the radio operates basically the same as any other dual band transceiver.  Unlike most other dual band radios which are “dual watch” only however, the PX-UV973 has full duplex operation (with some limitations).  With duplex mode “ON”, you can not only receive two transmissions at the same time (both are heard through the speaker or headphone simultaneously), but you can also receive while transmitting, like a telephone.  Its transmit frequency range is 136-174MHz and 400-480MHz, it has 128 memory channels, and can receive FM (broadcast band) radio stations.  It doesn’t have a LED flashlight, but does have a voice inversion scrambler with 8 different settings when some communications security is desired.  It also has a DTMF decoder, the last 6 DTMF tones received are decoded (0-9, #, *, and A-D) and displayed on the LCD screen.  There’s a couple stun options available as well, more on that in #3 below.

 

As I mentioned, I own a Baofeng UV-5R and also a couple different Puxing models (the PX-UV973 and the PX-777+), and I prefer the Puxings in most respects.  The PX-UV973 is twice the cost of the Baofeng though, so that might not be surprising.  The encoder knob on the top (next to the power/volume knob) makes programming the radio and changing frequencies much easier than the “up/down” buttons on the Baofeng IMO.  The programming seems more intuitive to me as well.  The case and controls are what you’d expect from a commercial radio.  The one drawback, and it’s a big one, is the battery/charger.  The radio itself gets 5 stars from me, but the standard battery/charger rates 1 star.  Its only a 1200mAH battery, good for maybe 36 hours of light use, and if you forget to remove it from the charger after it’s done charging it will cook the battery in a day or two.  I would not recommend purchasing this radio if your intent is to use it with the standard battery and charger it comes with.  I haven’t even bothered to test how long the standard battery lasts while using the radio in cross-band repeater mode, “not very long” is my guess though, and is the reason I suggest the 12v adapter and a much larger battery.

 

2) The free programming software for the PX-UV973 is fairly easy to understand if you’ve used other programming software before, although it can be tedious to program channels since it doesn’t allow importing any other file type, nor even allow cutting & pasting into the fields.  Chirp doesn’t support it (yet) either, so you’re pretty much stuck typing everything in by hand the first time you use it.  It uses the same programming cable and Windows device driver as the Baofeng/Wouxon.

 

3) In the “DTMF” section of the programming software you’ll find the “TX Stun”, “Cancel TX Stun”, “RX/TX Stun”, and “Cancel RX/TX Stun” entry fields.  If you’re not familiar with how “stun” works on a radio, it’s a code that you select that can be sent from a different radio to disable function(s) on this radio.  For the PX-UV973, the stun options allow disabling the transmitter (TX) and/or the receiver (RX) functions.  I’d suggest entering a unique (8-character) value in each of the four stun fields since they allow you to remotely control the radio.  If desired, and if your other radios support it, add the 2 codes for “TX Stun” and “Cancel TX Stun” into your DTMF autodial list on your other radios so you don’t need to memorize them.  This allows designated members of your group to quickly and easily send the DTMF tones to activate and deactivate the transmit ability of the PX-UV973 remotely, which might be required if it malfunctions, or if someone else determines the frequency and CTCSS/DCS setting you’re using and begins using your repeater.  You might not want to program the “RX/TX Stun” and “Cancel RX/TX Stun” values into your other radios autodial list however, but keep those 2 master codes completely private instead.  This is a kind of failsafe, where you can deactivate both the receive and transmit of the PX-UV973 remotely in the event it’s stolen or otherwise compromised.  And should one of your other radios be compromised, they won’t have access to those master codes stored in the autodial list either.  A last note on stunning the PX-UV973, once stunned the only way to reactivate it is to send the Cancel Stun code or reprogram it via the software.

 

4) What’s not entirely clear in the manual is that the cross-band repeater function only works when the radio is in the “frequency mode” of operation.  This is a little tricky to describe, but you change between the different modes of operation with the “VFO/MR” button on the radio.  If you want to manually enter the frequencies to cross-band between, just enter frequency mode and set the A and B frequencies manually for it to work.

 

If on the other hand you want to cross-band between 2 channels you already have stored in memory, then you’ll need to start in “channel mode” on “A”, tune to the memory channel you wish, then press the “VFO/MR” button to change the “A” side to the “frequency mode” of operation.  Then press the “A/B” button to switch to the “B” side, and repeat the above.  Hope that makes sense.  If you did leave the “A” side in channel mode and the “B” side in frequency mode, then anything received on A will get retransmitted out the B frequency – but something received on B will not be transmitted out the A frequency.  In effect this makes it uni-directional cross-banding, A –> B, but not B –> A.  Depending on your plan for deploying it, this might be desirable.

 

5) The Tram 1185 antenna is designed for use in the 2m and 70cm amateur bands (140-144MHz and 430-450MHz).  I tested it straight out of the box, no adjustments, and the SWR readings on a couple different frequency pairs outside those ranges never went above 2.0 on my meter.  YMMV however.

 

6) On range – Don’t expect to hoist it up a tree and start getting miraculously increased distance.  VHF/UHF is basically line of sight between the antennas, but with a lot of caveats.  There’s some line of sight calculators on the web to get an estimate of what you MIGHT be able to achieve, but the 5 (or 4) watt output of the radio will also be a limiting factor as will the sensitivity of the receiving radio.  If you use the calculators to get an estimate, remember that you want to enter the values for the height of your transmitter (5′ – 6′ for a handheld) and the height of the bucket repeater antenna.  Then, theoretically and everything else being equal, you’d be able to communicate with someone the same distance away on the opposite side of the bucket repeater from you.  Realistically, where it might have the most value is in situations where you need to communicate over a nearby hill or other obstruction, or if you need maybe an extra mile or two of additional range over flat terrain.

 

7) On bridging different radio equipment – Consider a TEOTWAWKI/WROL event where you need interoperability between different types of radio equipment.  Maybe you’re setting up a neighborhood watch and when you take inventory of what radio gear you and your neighbors have, you find there’s 1 marine band radio, 4 FRS/GMRS radios, 2 mobile/base VHF amateur radios (with MARS/CAP mods), a couple of dual band handhelds, and you have a bucket repeater.  No problem!  Set the bucket repeater to cross-band between a marine band frequency and a GMRS frequency, and now every radio has the ability for two-way communication with every other radio in the group (either directly, or via the bucket repeater).

 

8) For setting up a quick cross-band repeater system using 2 or more dual band radios and a bucket repeater, select an appropriate frequency in both the 136-174MHz and 400-480MHz ranges and choose a CTCSS/DCS code to use.  Set your dual band radios to use these frequencies/codes in the A and B displays, and set them to monitor for activity on both A and B.  For the UV-5R, that’s the “TDR (Dual Watch / Dual Reception)” mode.  It doesn’t matter which channel, A or B, that you set as the primary or which one you transmit on.

 

On the PX-UV973, set the A and B display to these same frequencies and CTCSS/DCS codes.  Remember to set both A and B to “frequency mode”.  In the menu, set “RPT” (repeater) to “ON”.

 

If you’ve set it up correctly, then when one radio transmits all the others will receive it either on the same frequency or via the retransmission from the bucket repeater on the other frequency (since you’re monitoring both for activity).  Which of the two frequencies each operator chooses to transmit on really doesn’t matter since, again, everyone is monitoring both frequencies anyway.

 

9) If you’ve read this far and are considering building one, you might be wondering how long it will run before needing to recharge the battery.  The answer depends on too many unknowns to give any accurate answer.  How many amp-hours is the battery, how well does it hold a charge, what’s the temperature outside, and how often and for how long each day will it be transmitting?  There’s probably more variables I missed, and in honesty I haven’t tested how long my system would function between charges either.  I have been thinking how I might add a small solar panel to mine though…

 

That’s it, hope you enjoyed the read and found something useful.  And please, if you decide to try this be very careful with the programming and configuration – and don’t do anything stupid.

 

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 The post above was an entry into the ModernSurvivalOnline.com Survival & Preparedness Guest Post Contest which from through December 31st.


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5 Comments

  1. Interesting —
    But you do have a very inefficient antenna. A vertical whip is only one half of the antenna — to operate efficiently, it needs a 1/4 wave ground plane underneath it. The paint can lid is fine for sticking the magnet on, but it doesn’t even come close to 1/4 wave in size on 2 meters –the required size for a good 1/4 wave ground plane on 2 mtrs is approximately 38 inches in dia.

  2. I was thinking the same thing. I have used filing cabinets, tops of cars, metal roofs etc. A common trash can lid will work or you could make a vertical dipole and hang it from the bottom of the bucket.

  3. Off subject, but I have a couple of radios, hand and mobile. Is there a periodic net we can participate in? Is there a preferred frequency on which we might make new friends?

  4. I’ve gotten noticeable improvement using a 19″ section of stranded copper wire as a rat-tail on my Baofeng for 2m, attached to the one of the case screws on the back of the unit. Never tried it with the Puxing, and never when it’s attached and using 70cm at all, but the Puxing does have a metal screw which holds the mic/speaker rubber weather flap in place and presumably is attached to the metal case internally. Or, some “coat hanger” radials attached to the paint can lid maybe.

  5. Nice looking idea. I’d offer that a roll-up J-Pole antenna (ex: N9TAX) could work well too and take up less (vertical)room in the bucket. The Roll-up could be hung from the bottom of the bucket for clearance as it was raised. Thanks for sharing!

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