UHF Wiring
Submitted: Tuesday, Mar 08, 2005 at 15:00
ThreadID:
21049
Views:
12059
Replies:
8
FollowUps:
15
This Thread has been Archived
will21
Which circuit should I wire my UHF into? How much current do UHFs typically draw (peak).
Cheers
Reply By: geocacher (djcache) - Tuesday, Mar 08, 2005 at 15:07
Tuesday, Mar 08, 2005 at 15:07
Either pick a permanant 12 v feed for the ability to leave it on when you have the ignition off (eg waiting to hear from someone meeting you at a
camp spot etc).
Or just use your cigarette lighter circuit (or a mobile phone circuit in later vehicles)
Most have an in line fuse of about 3-5 amps.
Peak current draw depends on age and efficiency of the UHF. The new GME Tx3200/3400 pull about 1.6 Amps on Tx and bugger all on standby. An older unit may pull up to 2.5 amps on Tx.
If you want a temporary install just put a cig plug on the lead and plug it in when you use it.
Dave
AnswerID:
101583
Reply By: Big Woody - Tuesday, Mar 08, 2005 at 18:57
Tuesday, Mar 08, 2005 at 18:57
Always wire radio's direct to the battery. It eliminates, as mentioned above, interference, potential for shorting out, and other issues. If you wire it through some other circuit, in effect you are working through 2 fuses.
The radio's may not draw much when receiving, but when transmitting the drop in voltage through other circuits can often be enough to affect your transmission signal and strength.
Finally, probably the most important reason for connecting radio's direct to the battery is the stability of the voltage, Circuit boards do not like fluctuations in the powere supply and when connecting through other circuits, every time you turn something on or off or start the engine etc. you will find the voltage varies significantly.
Cheers,
Brett
AnswerID:
101605
Reply By: geocacher (djcache) - Thursday, Mar 10, 2005 at 22:59
Thursday, Mar 10, 2005 at 22:59
If you wire it directly to the battery put your fuse as close as is practical (without being ridiculous about it) to the battery to prevent a short before the fuse smoking the wiring.
There's little point in fusing the -ve wire.
At 1.6 A draw it's unlikely that you will get enough voltage drop across a fuse to cause a problem but the contact quality between the crimped button (on glass fuses) or the female spade terminal on blade fuses can be a source of resistance.
You'd have to have a resistance of 0.5 ohm to 0.8 ohm to cause a 1 volt drop at the unit. With the engine running and an input tolerance typically between 11 - 15 volts being an absolute minimum on most units you would not cause any serious drop in radiated power. Even without the engine running and the battery sitting around 12.5 volts you'd struggle to notice it if at all.
More emitted RF is lost on these radios through less than optimal SWR now that nearly no-one tunes antennae after installation.
Dave
Dave
AnswerID:
102010
Follow Up By: Mad Dog (Australia) - Thursday, Mar 10, 2005 at 23:19
Thursday, Mar 10, 2005 at 23:19
Dave, the -ve is fused to prevent the radio chassis and antenna earth being used as a return path in case the battery to block earth becomes open circuit. All my Ham rigs came with both the - and + wires fused from the factory.
FollowupID:
359825
Follow Up By: geocacher (djcache) - Friday, Mar 11, 2005 at 00:17
Friday, Mar 11, 2005 at 00:17
Hi Ray,
I suppose that's a point but there'd be many other pieces of equipment that could do the same thing in a modern 4wd and we don't fuse the negative rail of any of them.
I don't think I'll bother.
Interestingly Codan don't fuse the negative rail of their gear that I've seen.
Must dig out the old theory books and have a read, you've got me curious.
Dave
FollowupID:
359830