|To:||rsgb lf group <[email protected]>|
|Subject:||Re: VLF: getting on 8.970kHz|
|From:||JACK ASKEW <[email protected]>|
|Date:||Thu, 7 Sep 2017 15:01:23 -0600 (MDT)|
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|References:||<[email protected]> <[email protected]> <[email protected]> <[email protected]>|
|Thread-topic:||getting on 8.970kHz|
Thank you for the technical support and reasons to go with a big coil instead of a big loop. The main reason I originally chose the loop was because of the size of the property we have here.
Lots of tall pine trees and 1 acre for all kinds of high antennas HF down to VLF. I won't rule out going with a big coil, it just seems like a lot of work involved having to wind such a big coil and a lot of $$ to spend too :-) Thanks for the link to the GPS receiver Stefan, we'll certainly check into it.
Thank you Rik for adding your opinion on the loop. Although the loop here has matched easier than I thought it would and the scopemeter shows virtually a perfect match, there is no proof as yet that the antenna has any efficiency or gets out at all.
I'm currently seeing 2.6A of RF with the meter in series with the ~76m of coax in the loop....so that's a lot of RF going somewhere.
Hopefully I'll get a small resonate loop thrown together and with my laptop I'll take a drive down the highway here and see how many km I can get before I loose the signal. That should give me a rough idea how good it is.
I'm only doing this project because it's challenging and besides a lot of fun seeing what can be done with minimal costs involved.
One of the big problems here is not having a good calibrated frequency counter I can trust. I have 2 Spectrum Lab programs on two different computers and both do not agree with each other as far as frequency calibration. Does anyone out there have a copy of a .usr file for 8970Hz that I could apply to SL?
Thanks for the good luck Joe, I might take an interest in your coil yet :-)
Thank you all...
73, Jack - VA7JX
From: "DK7FC" <[email protected]>
To: "rsgb lf group" <[email protected]>
Sent: Thursday, September 7, 2017 1:40:49 AM
Subject: Re: VLF: getting on 8.970kHz
Ok, so i'm continuing to write on the reflector. It is not at all a waste of time to read the conversation. Most potential newcomers are in a similar situation like you and they may be interested to see that there are more stations considering to get on the air down there, world wide! For example, IK1HSS tried to receive my VLF carrier transmission, but no one knows, except me. Sharing thoughts can never be a waste of time. Don't we all have loads of time available anyway? As long as someone own a TV, there must be more time than needed :-)...
Now, forget the loop for VLF transmissions. Your inv-L will give a very good radiator for VLF! Important parameters are height and capacity, you know. In the first steps you don't need QRO. 100 W from a normal audio PA is sufficient because the voltages will be very high! At 250 W on 8270 Hz i'm getting about 30 kV across the wire. Your wire and the isolators have to withstand that voltage. If the wire is to small, there will be partial discharges. It makes no sense to run 1 kW then. It would rather make sense to use a bigger wire or even more wire (capacity).... The first thing to concentrate on is a stable signal generator using 1 PPS.
Buy that one for example: https://www.amazon.com/XCSOURCE-Locating-Aircraft-Controller-TE624/dp/B01N2GK1YK/ref=sr_1_6?ie=UTF8&qid=1504772304&sr=8-6&keywords=neo-6m
You seem to have a high antenna capacity which is a big advantage. It is very promising that you can radiate a very strong signal. There is no time to loose!
For the coil i suggest to use a single layer coil using 0.4 mm or even 0.6 mm diameter wire on a tube with 0.3 m diameter or higher. It depends on the space you have for placing the coil. It should stay dry all the time!
You need patience to wind it but it is very relaxing. :-)
I recommend to build an analog amperemeter covering 0...1 A antenna current. It is trivial to build it. Just use a bridge rectifier out of fast switching diodes such as UF5404 and connect the meter to the DC side. The AC side is connected between coil and ground.
The coil is for compensating the capacitive component of the wire. The residual resistive component is transformed to the PA output impedance using a big ferrite transformer (toroid) which also provides galvanic decoupling.
Now, just order the GPS module, the wire and search for a suitable coil body :-)
PS: With that antenna, you can become the strongest amateur VLF station!
Am 06.09.2017 17:12, schrieb JACK ASKEW:
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