Quoted: ar-jedi..
As other have said your rig is inspirational.. I am trying to piece together enough knowledge to acquire the right equipment for my familie's disaster (hurricane) communications needs.. so I am following allot of your guidance. Thanks for the all the write ups, I'd say you almost have enough there for a published book. |
awww shucks...
Quoted: I don't think I need everything for RACES rig but I am looking at a mobile hf/uhf/vhf unit paired with a good HT to start. I am pretty much trying to keep thing to a minimum right now so we have comms for the following scenarios..
1) relaying status messages to family outside the disaster area 2) home to mobile (5-10 miles) 3) mobile to mobile in the event we use two vehicles to get the hell out of dodge 4) calls for emergency services |
IMHO, this is the very best way to approach your communications needs -- by defining what your system (collection of radios, antennas, and power sources) has to provide. and of course you want to allow for a little "growth" room, just in case.
Quoted: Anyways I have a few questions due to huge gaps in my knowledge at this point.. hopefully you didn't already cover these in some of the other posts... but here they are. |
these are good questions...
Quoted: When operating your rig off the battery do you ground the antenna or run an RF ground for the box to actual dirt.. |
this is highly dependent on the antenna setup. for some situations (such as an end fed antenna deployed at a field location) you will probably get much better performance by grounding the rig or antenna feed point. the issue of grounding is also instrumental in the operation of a vertical antenna -- the more the better. an added complexity is the bulk soil resistivity; in some locations your will find the ground is quite conductive, in others not so much. nevertheless, one good indicator is your SWR and the resultant difficulty you have getting a good match by either adjusting your antenna length and/or fiddling with a tuner. should you be unable to get the SWR to sit down with the rig or antenna ungrounded, try getting a ground of some type in place. remember that the better the match the antenna is, the less power you lose in the coax and tuner. so, strive for a good antenna setup, ESPECIALLY with QRP rigs.
Quoted: or does having everything connected to a common ground rod in the box cover everything? I know you covered this for home ops, but I didn't catch what procedure was while out in the field under battery power. |
the common power bus is just that, a power bus. normally it doesn't go anywhere from an RF perspective, especially not out in the field. so an adjunct ground wire must be equipped if you are going to ground at the rig, or as mentioned above you can usually do it at the feedpoint of the antenna. one way or the other may affect your SWR, so a little experimentation is usually in order.
Quoted: Also, in your wiring schematic I see you used a diode between the power supply and battery. |
i really need to fix that schematic. my charging circuit is somewhat more complicated than that schematic depicts. i wrote it up in another thread, hopefully the ARFCOM search facility can save my fingers from typing.
Quoted: Did you source these from Samlex? I read in their manual they specify utilizing both a isolating diode and charge limiting resistor... I assume these are mandatory for charging the batteries? |
for the charging circuit i use a diode (1N4004 type, available at radio shack and every other electronics outfit like IEI, Digi-Key, and Newark) to isolate my charging source. the latter is a DC/DC converter, you can see the picture here:
losdos.dyndns.org:8080/public/ham/races-box/construction/DSCN1067_sm.jpg
Quoted: Also, in your opinion or experience.. how well should the Samlex 1223 power supply deal with irregular voltage or distorted sine wave from a non regular generator AC? |
there will be no problem. as an added precaution against RF noise from external AC power, you may want to put a line filter in series with the AC power connection, near the Samlex supply. for an example of such, see the line filter in the foreground of
losdos.dyndns.org:8080/public/ham/races-box/construction/IMG_1836_sm.jpglosdos.dyndns.org:8080/public/ham/races-box/construction/IMG_1813_sm.jpgand the far right of
losdos.dyndns.org:8080/public/ham/races-box/construction/IMG_1808_sm_annotated_sm.jpg
Quoted: Finally SWR tuners.. your HF unit it nice with the built in tuner. |
one note about internal tuners. there is a cost/space/capability tradeoff with any tuner. most built-in tuners (such as you find on an Icom 703+) have somewhat limited matching capabilities. Icom advertises 3:1 but i and many others have found that the spec is quite conservative. most folks find that the 703+ will match 5:1 or so. this means that the radio will match most "reasonably resonant" antennas -- but it will not match an end-fed random wire with it's ~3000ohm impedance. for that type of application you need an external 4:1 balun or some other arrangement to better mate the antenna with the radio.
i'm not picking on the 703+ in particular here, either. even Icom's venerable $1400 internal tuner-equipped IC746Pro is only advertised to match 3:1. it does usually do better than that, but again there is a cost/space/capability tradeoff. an external tuner, in most cases, will do a better job -- but at additional cost and space.
Quoted: I am looking a the FT-875D that has no built in tuner. |
this is the case with almost all small form factor 100W radios (Icom 706MkIIG, Icom 7000, Yeasu 857/897, etc), so you are certainly not alone.
Quoted: Trying to keep things the number of comm pieces to a minimum right now and wondering if a tuner is a requirement. I halfway understand that the need for a tuner can be mitigated by adjusting the antennae length but to what degree? |
you can adjust the antenna length but there are 8 million variables which will fight you if you expect to operate in the field and on multiple bands. antenna height above the ground, nearby vegetation, soil resistivity, and so on. summary: get a tuner. it will resolve a lot of these issues and make operating more enjoyable. many external tuners have a control cable which connects to the radio -- you push the "TUNE" button on the radio, and the tuner goes to work to match the attached antenna. seconds later, you are ready to operate on your chosen frequency. it is very straightforward.
Quoted: Does the length need to be adjusted for separate frequencies in each band or can I make due with two lengths.. |
if we assume a horizontal dipole antenna, you basically need a length per band (160m, 80m, 40m, 20m, 10m, etc). in some cases there are means to use the same length antenna for multiple bands, due to the correlated odd harmonics. a 30 meter antenna can often be driven at 10m as well, and so on. performance may range from excellent to non-existent.
Quoted: one for HF, UHF/VHF respectively? |
not easily. there are HF antenna designs which are somewhat broadband/mutiband. the G5RV is an example, but you need at least 102' to stretch it out in, and the centerpoint has to be at least 35' off the ground. depending on your AO and SHTF status, this may be easy or impossible -- i don't know.
Quoted: I was thinking about using the yo-yo dipole you mentioned earlier in this thread when the FT-875 is stationary, but will I have to adjust it every time I change a frequency in HF? |
at a given length, you will be able to work one band, or in some cases "most" of one band. if you want to change to another hand, you will have to adjust the length. for this reason, many folks use a small auto-tuner, hang the yo-yo tenna out at it's maximum length, and let the tuner sort it out as you dial around the bands. this will at least give you something to work with, although a perfect match can again be found by adjusting the length of the antenna (plus or minus a foot) to suit the frequency of interest.
Quoted: And for mobile Ops.. are there car antennas that are tuned to work well for 2m, 70cm, and wideband EMS, NOAA freqs. |
any 2m/70cm antenna will receive NOAA and local law enforcement perfectly. dont' worry about this, there is plenty of signal there for a modern VHF/UHF ham radio despite the antenna not quite matching the frequency. heck, you can get perfect reception of local NOAA broadcasts with a 5" rubber duck antenna -- anything longer than that is simply going to help more.
Quoted: I don't think we'll need HF while driving down the road. |
this is my thinking as well. i don't operate HF mobile. many do however.
Quoted: I'd just get Yaesu's ATAS 120 antennae and use it both at home and on the road.. but some reviews are saying it is a marginal compromise antenna and prone to failure. |
i have read the ATAS 120 is the best thing since sliced bread.
i have also read the ATAS 120 is the most expensive 50ohm resistor ever made.
i don't have one but my engineering judgment tells me that the performance of the antenna is EXTREMELY dependent on the vehicle and the installation approach. as for reliability, a motor-driven screwdriver antenna tuned by RF feedback sense is by definition a fairly complex electro-mechanical system -- and one which is protected from the elements by rubber seals and what not. seals fail, anyone with a hydraulic tractor will tell you this...
Quoted: No need to go into extended answers on my part. But if you could point me in the right direction on some these questions I'd greatly appreciate it. I can then dig up the details from there. |
my $0.02:
your favorite radio + external autotuner (LDG or equivalent) + broadband antenna will suit you better than chasing perfect antenna lengths in blustery 15 degree weather.
ar-jedi