Thinking about another portable rig

Discussion in 'Ham Radio Discussions' started by WD0BCT, May 10, 2017.

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  1. WD0BCT

    WD0BCT Premium Subscriber QRZ Page

    I love operating my little FT 817 portable. Being limited by a stealth antenna at home it is really fun to get out in the foothills with my ATAS 25 and hear this little antenna outperform my patio antennas.

    My problem is working QRP. I'm relatively new to operating QRP and quite frankly it is laborious to both me and the stations I'm attempting to contact. Yes it is true that every now and then I hit paydirt and I intend to keep the 817 as it really requires little power (backpacking batteries is not fun). I enjoy taking the rig into the foothills outside of Denver and include my dog on the trips which means I have to pack in amenities for the dog and ground screw (for the dog tether...but it would probably make a good grounding point also).

    So I'm looking at the FT-891 as a possibility for more power in a portable rig. It draws 1-2A on receive and has cooling fans so it's specified amp draw of 23A means significantly more battery than the 817.

    I'm thinking that the amp draw could be reduced while operating on a battery between 11.7 and 12.7V Spec amperage is @ 13.8V. Also...I could crank the power output down to 50% and still have 10X the output of my 817.

    My question is big a battery would be required for the FT-891 operating at 50% power? I'm using a 5AH SLA with my 817 and get quite a few hours of operation. Unfortunately a lot of time is spent calling stations that hear me calling but can't quite copy me. I might be able to accommodate a 10-12AH SLA in my pack but how much operating time would that allow me with the FT 891?

    Comments and suggestions appreciated.
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The 5AH SLA is likely to discharge below 11.7V very fast if you start transmitting with the 891. Like maybe "seconds."

    I've used a 14AH SLA on my FT-857D a few times (older than 891, but draws the same kind of current) and for "receiving only" it will last pretty much all day, but for transmitting at 100W, maybe a few minutes. Literally, no joke -- a few minutes.

    A big LiPo pack would be a better choice. More power per cubic inch or ounce, by quite a lot.

    Then again, the 817 alone might make the grade if you simply use a better portable antenna than the little ATAS, which is not a "good" antenna on any band, and on 20m and lower frequencies is actually pretty poor, even with a good ground plane under it. I had an ATAS-120 on the roof of my van for a few months and compared with a 7' Hustler whip (mast+resonator+whip) on 20m it was poor, but on 40m was extremely poor. I could work stations easily with 5W on the Hustler who could not even tell I was there with the ATAS.
    AF6LJ likes this.
  3. WG8Z

    WG8Z Ham Member QRZ Page

    Antenna, antenna, antenna.
    KC8VWM likes this.
  4. KY5U

    KY5U Subscriber QRZ Page

    14AH means the battery theoretically could supply 14 amps for an hour. Two factors that effect this are max peak allowable current and 50% discharge value for the battery. Even at that, a radio which uses 23 amps during transmit has maybe 30 minutes or LESS of "talk time".

    Look at the specification comparison for automotive batteries which list amp hours, reserve amps. and cranking amps. Most will give you two hours talk time so if you are 50/50 listening and talking you may get 4 hours.
  5. KP4SX

    KP4SX XML Subscriber QRZ Page

    You better check with Burt before getting a second rig. That might be signs of a character flaw.
    WZ7U and WD0BCT like this.
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    It's really worse than that, since AH ratings are almost always based on C/10, so a 14AH battery is so rated because it can deliver 1.4A for 10 hours, not 14A for one hour.

    I've never seen a 14AH battery that can deliver 14A for one hour, I don't think it exists.

    "Cranking power" for auto batteries is based on 10 seconds.:)
    KC8VWM and KN7S like this.
  7. WD0BCT

    WD0BCT Premium Subscriber QRZ Page

    Good info....did you happen to try it at 50% output by any chance? The receiver on the 817 is actually pretty good...especially since it does not have DSP. But then again....out in the middle of nowhere noise is quite diminished. I do have 7' hamsticks on my patio that I could rig up as a ground mounted vertical with some radials. The problem with hiking in the foothills is that I can never predict how many accessible trees will be around. One can always gin up a vertical on a tripod. I think I'll pursue the hamsticks as a trial. I can't envision much difference between the hamstick and the ATAS 25 by looking at them. But looks are deceiving.

    I may have to look into more recent battery technology. Hauling a car battery around is certainly not fun. I don't think I wish to install a mobile rig in the vehicle but it may be the easiest way to operate 100W mobile.
  8. KC8VWM

    KC8VWM Ham Member QRZ Page

    Naw... hamsticks are not going to do it. Hamsticks are ok on 17m -10m, but shorter length antennas of any brand are not very good when you get down to 20m and below. Besides, the sunspots aren't what they used to be and you will need bigger and more efficient antennas to work the lower bands with any level of acceptable performance.

    Fully retractable, but yet "full size" wire dipole antennas really are your best bet for maximizing your signal when you're out on the trails.

    I came up with a telescopic painters pole with built in lightweight tripod solution for operating where there's no trees around.
    (yeah I know there's trees shown in this photo but try and work with me :) )


    Construction design photos / details:
    Last edited: May 10, 2017
    K7WFM likes this.
  9. NH6MA

    NH6MA Subscriber QRZ Page

    I'm going portable also.
    Look into LiFePO4 batteries and let your dogs pack them in. I'm not hiking so right now I'm looking at a 20ah battery that supposedly weighs in at 6 lbs. Check
    LiFePO4 is expensive but way lighter than the 30ah AGM I'm presently trailering around. Using an FT897 (boat anchor) here, usually working 50w with a 30ft EFRW.
    FT891/857 looking like a very nice option!

  10. WD0BCT

    WD0BCT Premium Subscriber QRZ Page

    My dog only weighs 35# and she is a Beagle. I can just see the look she would give me if I put a 6# pack on her!

    I'm beginning to think the QRP rig is the way to go for serious hiking. I'm also thinking CW only is the way to go for QRP also. However your cart looks like a good way to get a good sized battery from a car to the picnic bench. And I'm thinking that the 30AH or bigger battery would be required for the FT 857 or 891. I've seen some deep discharge 75AH Marine Batteries that would be ideal....but they weigh 50#. On a wheeled cart at a picnic ground it would not be bad. They wheel in beer kegs at that distance.

    The thing that amazes me about getting away from civilization is how quiet the background noise is. Add to that the number of signals getting in due to finding a relatively high point without buildings and I can say that my little ATAS 25 receives well and sets up and takes down quickly also. I'm generally alone (other than the dog) and rigging a tall pole with guys and a wire would present a bit of a challenge....doable but a challenge.

    How tall a pole can you support with that tripod Charlie? I'm sure I would require guy wires....wind can pick up quickly and briskly in the Rocky Mountains. Looks Loos are also a problem. If I'm not watching my antenna all the time folks like to march up to it to inspect it unannounced. I had one hiker and his boy tangle in the radial wires and upset the antenna. He seemed to get disgruntled when I suggested that he might have asked me if it was OK before he approached my antenna. I was about to suggest it could have been lethal but he hurried off without comment.

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