Dressler antennas

[reedio]

Anyone have experience using the Dressler Active antenna models? RE: ARA-500
Just like to find out if they can receive well. 150-156mHz and 800 Trunking freqs.Thanks DR

 

[N_Jay]

All an "active antenna" is, is an antenna and preamp bundled together.
Usually the antenna is not that good, and the preamp is trying to make up for it.

Get a good antenna, and then add a preamp if you are in a low noise location. It will work better and probably cost less.

 

[ka3jjz]

Actually Dressler antennas have had a terrific reputation in the HF world, but I haven't heard a thing about how well they work above that.

Generally speaking, N Jay is right - having an amp in an urban setting is asking for problems. Put up a good antenna - and the right coax - first, then add a preamp later.

I'm going to bet that you are in a restricted environment - one where you can't have antennas outdoors. There's a Larsen antenna that covers 150/400 and 800, and works quite well from all accounts. Put that on a mag mount on a metallic surface, preferably near a window and you're probably as good to go as you will get.

If you have an attic you can use, there are many other possibilities....

73s Mike

 

[reedio]

Thanks guys. DR

 

[zz0468]

I've actually had good luck with active antennas in a high noise environment. It takes a GOOD low noise preamp, and not too much gain. Done carefully, they can be effective, but never as effective as a full size antenna.

 

[jonny290]

All an "active antenna" is, is an antenna and preamp bundled together.
Usually the antenna is not that good, and the preamp is trying to make up for it.

Close, but true active antennas are generally short whips specifically matched to the preamp, and vice versa. This is done to reduce overload from nearby high-output transmitters - less metal in the air = less induced voltage on the antenna and less chance for preamp overload. This is why stapling a 70 foot long wire to commercial active antenna whips usually results in terrible performance.

They're rarely close to full-size wires, but I have had some good experiences with designs in the past, but more towards the HF end of things, where you can have the whip inside or in an attic for good performance and lack of static buildup (which can fry active antenna jfets). vhf/uhf gets too attenuated by walls and attics though, and usually you amplify all the crap and house noise around you instead.

 

[N_Jay]

I've actually had good luck with active antennas in a high noise environment. It takes a GOOD low noise preamp, and not too much gain. Done carefully, they can be effective, but never as effective as a full size antenna.

Hmmm, that seems odd. If you are in a high noise environment, I would agree with keeping the gain low, but the noise then becomes relatively irrelevant.

 

[N_Jay]

Close, but true active antennas are generally short whips specifically matched to the preamp, and vice versa.

Hu?

First an active antenna is an antenna with a pre-amp. I have know idea what you mean by a "TRUE" active antenna.
(I find people use the prefix "true" to mean "What I know, and not what you think"):roll:

How do you match an untuned whip to anything across a wide bandwidth?

This is done to reduce overload from nearby high-output transmitters - less metal in the air = less induced voltage on the antenna and less chance for preamp overload.

Yes, as I said, a bad antenna and an amp to try to compensate. It is NEVER better than a good antenna.

This is why stapling a 70 foot long wire to commercial active antenna whips usually results in terrible performance.

Back to why preamps are usually useless if you have a good antenna.

They're rarely close to full-size wires,

Hu?
You really believe that?

I have had some good experiences with designs in the past, but more towards the HF end of things, where you can have the whip inside or in an attic for good performance and lack of static buildup (which can fry active antenna jfets.

If your reception is limited due to static noise you have whole different issues, and the active antenna (or any other low gain, amplified set up is a fix, but not the best fix.

vhf/uhf gets too attenuated by walls and attics though, and usually you amplify all the crap and house noise around you instead.

That is a good way to explain it to people who do not want to study it any further.:roll: :lol:

 

[zz0468]

Hmmm, that seems odd. If you are in a high noise environment, I would agree with keeping the gain low, but the noise then becomes relatively irrelevant.

I could give you the specific circumstances were it worked, but I couldn't necessarily tell you WHY it worked. Years ago, I used to live in an area that had some 500kv lines right across the street. Typical wire antennas, either a random wire or a resonant dipole produced more hash than signal. Shielded loopsticks worked well, and so did an 18" whip on a low noise preamp. Low noise in this case was <2db nf.

Presumably, the short whip was even less effective in capturing 60 cycles than it was on hf, 3-30 MHz. The output of the preamp was padded to the point that strong signals were approxamately as strong as they were when received on a random wire, maybe 10 db. And there were conditions where the wire outperformed the 18" whip.

I did quite a bit of experimentation there, and learned to love loop antennas. But that active antenna did surprisingly well. It was a home built preamp with a u310 fet, btw.

 

[N_Jay]

The nice then about antennas is that unless you are very careful with the design of any "experiment", there are enough seemingly random factors to prove anyone right (or wrong).

I'll stick with finding that they work according to theory. I am rarely surprised.

 

[zz0468]

It all comes back to what was said in another thread a couple of weeks ago... signal to noise. Antenna theory is pretty mature, and there isn't much new under the sun that hasn't already been proven in theory. But sometimes one can get lucky with a semi-educated guess.

 

[prcguy]

If you live in an area where overloading a preamp is not a problem, an active antenna or preamp can really make an improvement. Most scanners and wide band receivers have a crappy noise figure, probably 10dB or so and all the coax loss between the antenna and receiver adds to the system noise figure. A good preamp at the antenna can set the system noise figure to a very low number and make up for coax losses.
About 10yrs ago I got 2 sample Dressler ARA-2000 series antennas to test on an outdoor antenna range and compare to a Diamond Discone. The Dressler was not very good and somewhere around the lower 150MHz range the Discone picked up more gain down to about 80MHz and again where the 50MHz whip resonated. At best the Dressler was several dB better in the UHF range and a little better still around 900MHz. Both Dressler samples measured the same, so they were not defective. At the time the Dressler rep claimed he used and preferred a Discone with a seperete Dressler preamp at the antenna. I since picked up a Dressler ARA-500 cheap on Epay and did some casual testing. It seems to work ok for VHF/ UHF aircraft and other stuff up through 500MHz. Inside the radome is a PC board "fat dipole" with capacity hats and it resonates at 145Mhz without the preamp attached.
prcguy