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Wire Gauge VS Battery – Ham Radio

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  1. Sep 3, 2013 #1
    I have a 75w 2meter mobile transceiver (Yaesu FT-2900R – 13.8 volts DC, 15 Amp max draw, min draw is .3 A-.7 A ) that I would like to use in a camp type setup. The power source will be Two 12volt batteries (not dedicated) on a small enclosed utility trailer, which will be 20’-50’ away from the transceiver. The transceiver will be used mostly to monitor the channel (low power), with occasional transmitting. I have thought of several different ways to set this up, and there are pros and cons to each. Any thoughts on what would be a quality set-up, without wasting money would be appreciated. My main concern is that the transceiver does not like low voltages, and will reset if the batteries are not in good condition.

    Here I the options I am thinking of. The components are listed in order, with the first item listed being the one closest to the trailer batteries, and the last item being the transceiver.

    Option 1)
    a) 20’-50’ of Heavy Gauge Wire
    b) Transceiver

    Option 2)
    a) Battery Booster (MFJ-4416B - $150 - http://www.hamradio.com/detail.cfm?pid=H0-008745)
    b) 20’-50’ of Heavy/Light? Gauge Wire
    c) Transceiver

    Option 3)
    a) 20’-50’ of Heavy/Light? Gauge Wire
    b) Battery Booster
    c) Transceiver

    Option 4)
    a) 20’-50’ of Light Gauge Wire
    b) Third Battery
    c) Transceiver

    Option 5)
    a) 20’-50’ of Light Gauge Wire
    b) Third Battery
    c) Battery Booster
    d) Transceiver

    Option 6)
    a) Battery Booster
    b) 20’-50’ of Light Gauge Wire
    c) Third Battery
    d) Transceiver

    Option 7)
    a) 1,600 watt Inverter (Already Own This, and a 2,500 watt Inverter)
    b) 20’-50’ Standard A/C Extension Cord
    c) Power Supply (32 Amp - ALINCO DM-330MVT - $160 - http://www.hamradio.com/detail.cfm?pid=H0-003728)
    d) Transceiver

    Here are some of the pros/cons that I see. Option 1 seems like the standard installation; however, heavy wire gauge is expensive, difficult to work with, difficult to splice, difficult to roll-up, and to store; so I don’t really like this option (I am guessing this would need to be heavier than 8awg, and anything over 8awg I prefer not to work with.) I think when transmitting it will reset the transceiver with this installation as well. Options 4, 5, & 6 require another battery which is nice, because then I could use the transceiver and battery together as a stand-alone unit when needed; however, batteries are expensive and don’t last long, so this option seems like a maintenance issue (I could partially mitigate the maintenance issue by using a car jumper battery, since then it will have dual purpose, but I don’t think they are deep cycle, which would be bad for this installation.) Option 7 is nice because I would like to have a power supply. I would also be able to more easily move this setup to my house and use it as a base; however, this is not necessary. The downside to option 7 is that it seems inefficient to convert DC power to AC then back to DC, I am guessing this will be an additional drain on my batteries (but I do not know how much.) This would also mean I need to run the inverter continuously; which I would rather not, due to wear, and the noise from the inverter fan (since people might be sleeping in the trailer, though this concern is minimal.)

    QUESTIONS:
    1) What seems like the best installation option?
    2) What is an appropriate wire gauge?
    3) What would be an appropriate Third battery size and type?
     
  2. jcsd
  3. Sep 5, 2013 #2

    Baluncore

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    Ham Radio is supposed to be experimental. You are clearly over-thinking the problem.
    Use what you have available now. If it fails, get heavier gauge wire from a scrap yard.
     
  4. Sep 5, 2013 #3

    berkeman

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    As long as you are okay with the cost, I'd go with Option #3 and put the Battery Booster at the transceiver.
     
  5. Sep 5, 2013 #4

    davenn

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    you are going to get a dreadful voltage drop over that sort of length of cable
    I wouldn't even be considering anything more than a few feet, 8 to 10 at the shear most

    Take the radio to the batteries or the batteries to the radio
    going from my own and other operator's experiences, anything other than that and you are likely to be very disappointed

    on my transceiver gear I keep all power feeds to less than 10 ft and they ONLY get to that length in a mobile installation when running from battery into passenger compartment etc.

    On the home base I keep ALL power leads to under 5ft, preferably 2 - 3 ft at the most
    Its really easy to put you multimeter across the input power terminals to the high power radio and hit TX
    and watch the voltage sag several volts on a long feed 10 ft or greater
    This results in a substantial drop in your transmitted power out!!

    Dave
     
  6. Sep 6, 2013 #5

    Baluncore

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    If you apply the KISS principle you will find a 50' length of power cable and a battery with the same voltage and chemistry as your main supply. Put the battery next to the transceiver and keep it topped up through the power cable. I use two conductor 25 sq mm aluminium overhead power cable. It is light weight and very useful. Problem solved.

    You do not need to run an inverter to HV AC and switch-mode power supply to return it back to 14V. That will just be inefficient and generate RF noise. 80% x 80% = 64%. It is really not needed. Likewise, a battery booster is unnecessary. You do not need more than 12.5V for your transceiver to function. Since you spend most of your time in RX mode, the less switching you have the more economic will be your battery supply.

    IMO 75W on the 2m band is overkill. You will be limited by propagation, your antenna and your feed-line. (High power is really only needed when using low SWR coaxial cable such as RG58). If you can hear another transmitter you should be able to communicate on 10W or less. Transmitter output power should be the least of your concerns. QRP.
     
  7. Sep 6, 2013 #6

    davenn

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    not at all

    well that's natural for any band HF, VHF, UHF and up nothing specific for 2M


    ohhhh garbage .... Low SWR cable such as RG58 what on earth does that mean ?? no such thing, that sounds like CB jargon nonsense

    with higher loss cable like RG58, more power means you are just heating up the cable more .... use decent cable RG213, LMR400 etc and lower your TX and RX losses regardless of the power levels you use
    The only place I use RG58 is within a vehicle where the larger coax cables are too large and inflexible to get between the radio and antenna

    a few weeks ago, mounted a 23cm band radio in the car and grudgenly had to use RG58, but I used the bare minimum length ... 2 metres ( ~ 6 ft)

    again, not totally true ..... the other station may be running 100W, and you aint likely get back to him on 10W, unless there is exceptional propagation and you 10W may give him an S-point or 2

    hahaha
    Baluncore ... you are obviously not familiar with the Ol' ham saying....
    Life Is Too Short For QRP !!!


    cheers
    Dave
    VK2TDN
     
    Last edited: Sep 6, 2013
  8. Sep 6, 2013 #7

    Baluncore

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    There is very little energy reflected back with RG58. What manages to get to the antenna and is unlucky enough to be reflected, is very lucky if it gets back to the transmatch. It may be counter-intuitive, but that results in a Low SWR across the band. That's why I only use Heliax.

    The difference between 10W and 75W is only 9dB. It is statistically rare that those extra 65W are needed. Cheap power prevents amateurs building better antennas and feeders. I would change band for better propagation rather than warm up the linear.

    I think you meant; hi hi.
    Cheers
    Baluncore
    Ex: VNA7
     
  9. Sep 6, 2013 #8

    davenn

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    Dont muddle Low SWR and Low loss .... a given piece of cable doesnt have low or hi SWR
    you will NEVER see in the list of cable characteristics, its SWR rating ... cuz it doesnt exist
    You will however see its rated attenuation loss / metre (foot) and in general smaller diameter cable such as RG58 (1/4" dia.) will have much higher attenuation than larger diameter cables for a given frequency.

    There's very little reflected energy in ANY cable as long as its terminated correctly.
    its doesnt matter if you are using crappy RG58 or high quality Heliax or something like Andrews 7/8" cellflex. Any reflected enery is a result of poorly installed connectors or a poorly matched antenna causing " impedance bumps ( places where there is a change in boundary conditions)" therefore reflection points. Its why connectors like the N-Type, APC7, ones for heliax etc are made in such a way to ensure the transition from cable to connectors and back to cable is as smooth as possible.

    not when you are doing VHF and up weak signal work, have proved that over and over again when doing hilltopping activities. Even in a limited amount of work I have done on HF I could see the difference .... my first HF radio was a Kenwood TS120S @ 10 W, I really struggled to be heard and after 12 months of that I almost totally gave up on HF. I upgraded to a Yaesu FT 897D @ 100W and I started working all sorts of countries around the world. Got a Kenwood TS2000X, ~ 18 months ago 100W on HF through 6M to 2M, 50W on 70cm and 10W on 23cm. Havent even used it on HF, most of my activities are on 1000GHz and up.

    yes there is a lot of truth in that, tho I would say SOME amateurs, there are still those of us that work hard to produce a good installation.

    well on HF you have that choice, propagation varies greatly from band to band and during the day/night. That doesnt happen so much on VHF and up and if you want to do any long haul work where there is no prop. enhancement such as ducting, sporadic E or auroral then power really counts if you want to make the distance :smile:

    I think you meant; hi hi.
    Cheers
    Baluncore
    Ex: VNA7[/QUOTE]

    .... ._ .... ._ I gave up on .... .. .... .. a long time ago as did many of the other guys :wink:


    well between the 2 of us we managed to disrail the thread
    hopefully the OP'er learnt something out of it all

    regards
    Dave
     
  10. Sep 6, 2013 #9
    So are you saying a good experimenter should not think through the experiment? Half the fun is over thinking it, you get more time with your hobby than just your actual time doing it.

    That is why i had option 5; which is what i think am going with. I agree, this a problem, hence the post. The idea is that a small battery should be able to handle short transmissions, and the wire to the large batteries should sufficiently charge the small battery while receiving, and before the next transmission.

    I knew it would be inefficient, but i am starting to see how bad it would be. I didn't really think about the interference, thanks, good advice, i wont do this. I may not need more than 12.5v, but batteries only put out 12v when topped off. I am thinking the battery booster will give me a little more transmit time out of the small battery while the big batteries are trying to charge the small one. The booster has a coax input to sense RF and keep it from running on Rx. This should make it more economical for the battery, i am just hoping it doesn't effect the signal with the extra splice.

    Not overkill (plus i just said the radio is 75w, not necessarily that i run it at that, though i will :P)I run mostly on simplex in the desert with rolling hills. I have been using a handheld at camp with a base antenna, and have been having a hard time reaching the higher power mobiles just 5+ miles away. Plus i use the Yaesu ARTS feature, which i am sure could benefit from higher power.

    I run LMR400 with a double 5/8 wave ground plane diamond antenna on a 25' fiberglass pole. I have tested this setup and the SWR is as low as my meter could reliably detect. I don't really know how to top that (yagi doesn't count, because who knows what direction i am going to be in.) I have only used this setup at home so far. The antenna i was having trouble with before was a homemade ladder line j-pole on a 35' pole. It had horrible SWR, but it beat the handheld antenna. I have already invested in many 2M radios, so a new band doesn't seem worth it (plus is any band any better for simplex reliable 5-20mi communications, like i am doing?) I just want the base to be as reliable as possible. I communicate with off-roaders and if someone gets in trouble, its good to have a line of communication. There are repeaters, but most the other operators arn't as comfortable on the repeater.

    Certainly. This is all very interesting and helpfull
     
  11. Sep 7, 2013 #10

    Averagesupernova

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    davenn you are missing the point about low SWR cable. The point is that RG58 is considered lossy enough so that no matter how poorly the match is at the antenna end the reflected power is seriously reduced at the transmitter. Example:
    -
    For the sake of argument we will say that a 100 foot piece of transmission line has a 10 db loss at the frequency in question. We hook the transmitter to the line and forget to hook the antenna which results in the worst of matches. 100% of the power that reaches the antenna end is reflected back to the transmitter. Ok, some quick math. Transmitter is set up to deliver 100 watts at the output. 10 db of loss over the 100 feet to the antenna results in only 10 watts making it to the antenna end. This 10 watts is reflected back to the transmitter and encounters another 10 db of loss along the way back. Now we have a reflected power measured at the transmitter of 1 watt. Doesn't look too bad on an SWR meter now does it? Try this with less lossy cable things won't appear as rosy on the old SWR meter.
     
  12. Sep 7, 2013 #11

    davenn

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    not really ....
    not when the observed SWR is basically meaningless. I want to know that my forward/reflected power readings are a result of a mismatched or untuned antenna.
    If crappy coax is just hiding an antenna fault, then Im in a bad situation.

    A dummy load looks great on a SWR meter too, but make a good antenna, is doesnt :wink:

    Dave
     
  13. Sep 7, 2013 #12

    Averagesupernova

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    No one has said crappy coax is not hiding an antenna fault. In fact baluncore has said exactly the opposite and so have I. You are agreeing with us yet saying we are wrong. Again, you have missed the point. The whole point of higher transmitter power with lossy coax was so that you ended up with something by the time you get to the antenna. Admittedly, baluncore came about it in an unconventional manner but it doesn't change the fact that he is right. It may not be good practice to run higher power with a mismatch on lossy coax but it doesn't change the basics.
     
  14. Sep 7, 2013 #13

    berkeman

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    I think we're all on the same page here:

    ** use low-loss coax for any long runs (and avoid long coax runs where possible)

    ** if you have to use lossy coax for a moderate run, check your SWR first with a short run of the coax to be sure your antenna is well matched to the coax (I've seen cases of counterpoises being forgotten on a vertical antenna, and the mismatch was so bad that the station wasn't readable until he checked his SWR and went Doh!)

    And I have to agree that more power is important on the 2m band in some cases. The geography here in Silicon Valley makes it difficult for some stations to hit our Resource Repeater, and more power helps a lot in Simplex Tactical Nets that span several cities of our local Tri-City area.

    :smile:
     
  15. Sep 9, 2013 #14

    Baluncore

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    Parallel batteries with the same chemistry all provide current when demanded by the load, and they all take charge while charging, but they do not exchange energy, or charge each other when one is “a bit down”. The problem arises because to top up a lead acid battery requires a slight over-voltage to reverse the electrode's surface polarisation. A fully charged, but idle, 12V battery will produce typically only 12.6V, but it is necessary to maintain 13.8V in order to reliably float charge the battery. For this reason, simply connecting local and remote batteries will require some way to make up the 1.2V difference if you want one to charge the other.

    There are a couple of alternatives. One would be to use super-capacitors at the transceiver end instead of a battery. Another would be to use a battery booster between the two battery locations.
    Remember that the voltage lost in the connection cable resistance is added to the 1.2V polarisation.
     
  16. Sep 9, 2013 #15

    berkeman

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    @Baluncore -- very interesting point. I didn't know or appreciate the part about having to charge at the higher voltage to overcome the electrode polarization. Thanks.

    @OP (and others) -- I was just posting some safety tips in another thread for a person who is building his first AC Mains based power supply, and my comments about the fuse portion reminded me how important it is to put a fuse in-line with your supply battery's + lead right away before the wiring goes anywhere. Let's just say that I had a wake-up call with one of my HAM battery backup boxes and, um, well luckily the fire did not spread enough to cause major damage to my apartment or me. So now I always put an in-line fuse right at the + terminal output of all of my battery installations. :smile:
     
  17. Sep 10, 2013 #16
    Well I already bought a battery booster, so I suppose I could use that to help with the charging issue Baluncore described (thanks for that by the way, I was not aware.) The installation would then be like option 6 instead of 5. I am re-thinking this installation though. To avoid the third battery, I am thinking I will just mount all the transceiver near the main power source, and extend the mic and speaker. I have an external speaker which will be easy enough to extend (hopefully I won’t lose too much sound with the long run.) The mic appears to be a standard telephone RJ-?, so I think I could just buy a telephone extension cord (hopefully the length doesn’t cause any issues?) I would not have easy access to most of the controls with this installation; however, this is not a major concern. I really will only be on one channel. Now the battery booster seems a bit superfluous, maybe I could return it, or just install it anyway.
     
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