Discussion in 'Mobile Radio Systems' started by NO6O, Jan 6, 2011.
You must have a BIG car to hold all that gear!
You got an image of that awesome mobile set-up you can post? I'm especially interested in the rotator and the frequency standard!
It's a van and all that stuff normally isn't in it unless I'm contesting in the field (VHF-UHF Roving).
In that case, most of the "gear" is actually in an enclosure on the roof, along with the antennas and rotator. But a ton of cabling is involved, for sure.
You've actually sat in the vehicle I use for this (the van), but not with all the stuff installed. It only gets installed for roving.
I do have some photos, but Wayne N6NB's done a far better job of documenting what is done, and all the gear I described is of Wayne's design, and built from a combination of commercially available items and homebrew ones.
He discusses the roving stations, and includes a lot of good photos, here:
Essentially, a small HF rig (FT-857D or equivalent) is used in the vehicle as the I.F. baseband system for a bunch of transverters located on the roof. The transverters/rubidum standard/solid state amplifiers/relay system is all in a weatherproof, ventilated enclosure (with a fan or fans) and all the antennas are mounted to that enclosure to keep the feedlines very short, typically 3' or less. That whole mess attaches to a platform which is bolted to the top of a Yaesu G800A rotator, and the rotator is bolted to a larger platform which is held in place by the vehicle roof racks.
What goes up to the rooftop box is 12Vdc power; 28 MHz I.F. TX/RX line; rotator control cable; two more feedlines for 50 MHz and 144 MHz RF, since the 857D is used "directly" on those bands without any transverters; data lines to control the rooftop transverter relay system; etc. Except for 6/2 meters, typically all the antenna feedlines just go into the rooftop box to attach to the transverters or amplifiers there. The ultra stable frequency standard is required for the higher band transverters on 5.7 and 10.3 GHz, otherwise a regular crystal oscillator (multiplied a zillion times for the L.O.) isn't nearly stable enough and you end up searching for everybody, because nobody comes out on the frequency your dial would indicate.
By having all the rover stations equipped with a rubidium standard, when we dial each other up, even at 10.3 GHz, we're all within 1 kHz or so.
Down in the vehicle is the "bandswitch" control that flips relays up above to crank in the correct transverter for each band. The vehicle also includes an AC power inverter for rotator power.
Wayne's got this down to a science, and a whole 10-band station can be installed in about an hour, and functionally tested.
BTW in his own RV, Wayne also has a 4kW gas generator and kilowatt (tube type) amplifiers for 50/144 MHz, so he can be LOUD. Most don't have that.
U have a rotator mounted to your car? Can I see a pic of the antenna it's turning? You must attract quite a bit of attention going down the road.
Rats! I should have read all the posts before responding. I see I am not the only one who caught the "rotator in a mobile set up". LOL! Steve, is there anything in ham radio you haven't done or bought? Hehehehehe!
Steve...just 'cuz somebody called me out on something like this in a different forum I just gotta pass along the favor.
That's not a mobile rig...it's portable. Or do you really use a beam while in motion!
[edit after reading more carefully]
Oh, excuse me....."roving station." Much clearer!
It's really a mobile station, with not just one beam, but actually 7 or 8 of them, plus a dual-band (dual mode feed) dish for 5.7 and 10.3 GHz. It can all rotate while driving, and it does, to work stations in different directions while heading down the freeway.
Of course "beams" for these bands are pretty small. Some of the rooftop systems have 33 element loop yagis for 902 and 1296 MHz, and those are about the biggest ones. They're still small.
There are frequent references on the web stating that you should not run RF and power cabling together, even from automobile manufacturers. Well.... that's a bit of a stretch.
If you properly install your antennas, and you properly install your DC wiring, you could enclose them in a common, ungrounded shield, and never have a problem. However...
Folks just don't (or won't) take the time to properly install their antennas. As a result, there ends up being a lot of common mode current flowing on the control cables, coax, and even the DC power cables. And, running ground straps hither and yon, won't solve the problem.
Probably the most important attribute is simply this: It is the metal mass under the antenna that counts, not what's along side!