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Review Comments Hirschmann GPS combo antenna
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ScottMoffatt
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Joined: Oct 02, 2005
Posts: 10

PostPosted: Mon Oct 09, 2006 1:41 am    Post subject: Reply with quote

In the review you mention that you obtained power from an interior light feed.
That's an unswitched supply. This unit draws 40mA for the AM/FM preamp.
If you're using the car every day, this won't be an issue, but you could find it won't start after being stood a week.
...and when car batteries have been deep discharged just once, the end of their life approaches rapidly.

The standard application for these antennas is to be powered from the head unit's antenna/amplifier control output. If you are replacing one bee-sting with another, this should already be present.

But, if you're using the aerial just for a TMC application (using the existing vehicle aerial for the radio), it's probably best to source an auxiliary-switched supply.

The GPS preamp section should be powered by the GPS receiver, so there's no issue there.

On the whole, I'm not a fan of under-size aerials with preamps to supposedly make up for the lack of performance. The noise figure of the preamps isn't exactly brilliant. Signal level is a bit higher than with a plain aerial, but C/N ratio is far worse. (DaRacerz echoes this)
The French had it right when they fitted plain 750mm fibreglass whip aerials on the roof for FM radio.
I agree with kiptower - WOT NO DAB?
I've fitted my Beemer with one of those French whip aerials from the scrappy, cut down to 325mm for DAB and it's far better than my mate's 70 amplified one!

Scott.
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mikealder
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Joined: Jan 14, 2005
Posts: 19638
Location: Blackpool , Lancs

PostPosted: Mon Oct 09, 2006 4:15 am    Post subject: Reply with quote

With respect to where I connected the power feed to the aerial, it is via a switch so I can turn it off, although it is very rare for the car to be stood for more than a day. I have provisioned to turn it off, but thanks for pointing that out.
It is a shame the unit won't do DAB, and I would agree the aerial is a compromise when compared to a full length unit that requires no amplification, the problem with full length is down to practicality - car parks, low height clearance etc = damaged aerial.
What I needed was something to replace a damaged unit to feed an FM signal to a TMC unit, this is the prime function which it does better than the previous damaged unit, the other capabilities of the device are there when required - Mike
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