Of course, Mike reminded me, I assumed a receiver of choice will have
things like agc fast, slow, on/off and so on plus a noise blanker. One
reason for suggesting various tuned circuits depends on the receiver's
front end selectivity and IM distortion.
Yes, Chris, I have an active whip with a gain of 100, it will provide 8V
peak to peak output before clipping but that's still not enough and it
suffers from IM! I'm drawing the circuit and adding a tuned circuit in
order to model the response.
Could I suggest trying one of these "split field" antennas. I'm working
on one now, it seemed to give good results just sitting on the workshop
floor and will take care of the "front end " tuning. The only problem is
mechanical, how to get a "barrel" of ferrite rods into a weatherproof
container and mount it in a high place and, of course, it's directional.
Hugh, M0DSZ
On 20/04/2016 11:51, Chris Wilson wrote:
Hello Mike,
Wednesday, April 20, 2016
I have been using a home built active antenna a friend bought me off
Ebay, probably a close copy of the "proper" one I feel guilty about
having a clone of. It's in a home built capped waste water pipe
housing near the top of my lattice mast, on its fibreglass topmost
section. I have found it does not work as well feeding my dedicated LF
receiver, one of these:
http://icas.to/lineup/idc-136ii-kit-eng.htm
as does my transmitting, resonant aerial. That's a vertical with a
horizontal quad loop as its top hat.
This active antenna is just using the dedicated PCB section as the
antenna, maybe I should add an external piece of stiff wire to it? I
am certainly not plagued by any strong transmissions near here, it's
normally our own electric fences that cause me issues.But sharing a TX
aerial with a receiver is a pain. As is sharing my HF loop with an LF
TX.... :( I need more aerials, but I do not need a divorce. Difficult!
I would and could invest in a dedicated receiver for LF though,
something hopefully better than the one in the link above. Space isn't
an issue. Any suggestions for something commercially available? I am
not incompetent at building stuff, I simply do not have the time at
the moment, due to work. I have used my Kenwood TS-590 as an LF
receiver, but again, as it's also the exciter form y LF amp, it's a
pain swapping stuff about. I really want something I can leave on RX
all the time like the IDC-136ii above, but better... Thanks.
Best regards,
Chris 2E0ILY mailto:[email protected]
My part time LF grabber is at http://www.chriswilson.tv/grabber.html
Hugh's advice is excellent - adequate sensitvity, a resonant antenna
and good front-end filtering. I would add good dynamic range, an
effective noise blanker and ideally a way to reduce or switch off the
AGC. After fittng the filters, there should still be a large
difference in background noise when the antenna is connected.
Local noise is a major factor, and it may be necessary to have a
separate receive antenna, situated and oriented away from the noise
source.
Lastly, it can help to have a directional (preferably steerable)
antenna to reduce lightning noise away from the wanted direction.
Mike, G3XDV
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