## 70197Re: [softrock40] Antenna problems?

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• Nov 18, 2012
There are a number of DOS and Windows loop calculation applications like mloop31, loopcalc.exe, RJELOOP1,  etc. available via a search engine.
With the programs you can model a loop - by providing loop size (total length), diameter of coax and frequency it will give values of capacitors, etc.

Online loop calculator http://www.66pacific.com/calculators/small_tx_loop_calc.aspx

RG213 is best as the self capacitance is much less than RG58 and higher Q.

Also practical articles - so many as to make your head spin.
http://www.rsars.org.uk/ELIBRARY/ANTENNAS%20DOCS/Portable%20HF%20Loop%20%2040-10m%20-%20G8ODE%20iss%201.3%20.pdf

I am sure you can build a loop that's easily transportable to cover all HF bands 40m - 10m.

If you are using the loop only for RX you can ignore the voltage in the results - the programs ask for TX power and returns the voltage (KV) across the capacitor for the amount of power. The plate spacing for the capacitor is not relevant if RX only.

My first loop was made from 1m of 3/8" soft copper and I used a capacitor that limited my TX power to 7W SSB and I worked all over Europe on 40m with excellent results with the loop indoors on the upstairs landing.

You can lean the loop up against a wall or erected in any convenient spot and it doesn't need height.

Using a gamma match is easier to adjust than a coupling loop and lessens what you have to take with you. I use gamma matching on all my loops from the 1m diameter to the 13 feet diameter.
73 ... Sid.

On 18/11/12 23:27, Ulf Holt Gmail wrote:
I will try this construction, but I have a few questions.
1) what dimensions are we talking about?
2) how large capacitor and do I have to pick a frequency on the receiver and then go back to the antenna and tune the capacitor, for the optimal signal? As it is now, I can't hear any signals at all.
3) what kind of coax? The only coax I could get my hands on here is 60 ohm coax for surveillance cameras,  which i had to use for feeding the receiver,but off course when I go to Bangkok later this week, I can get whatever I want. I suppose RG213 would be a possible choice. RG58 is too soft if the ring has a diameter larger 20 - 30 cm. maybe I should replace the feeder, using RG58 instead?

Ulf

Den 19. nov. 2012 kl. 04:29 skrev "junius fox" <jfox05@...>:

Hello,  You can construct a nice receiving antenna out of coax and a inexpensive plastic variable that are used in cheap radios.
the antenna is shown below:

----- Original Message -----
From: Ulf Holt
Sent: Sunday, November 18, 2012 2:44 AM
Subject: [softrock40] Antenna problems?

As I have mentioned in my request for Software (I have now choosen to use PowerSDR-iq) I have problems reveiving anything. I got a Chinese AM station the other day, so I suppose the RX Ensemble II receiver is working in some way or another, but I am not very impressed of the sensivity. My problem is how to put up an antenna to test this radio.

I am on a long vaccation in Thailand, and we live on second flor in a building that is 18 flors, and the only chanse for me is a balcony which is not very large and east bound. To make things even worse, both sides are shielded with concrete, so I only have an free opening that is about 1.8 m x 4 m.  I tried to put up a simple wire about 4 meter long, and connected it to the inner cord of a coax, which I connected to the receiver. A really bad solution, but I still would expect to pick up something, but I cannot get anything at all. If I remove the antenna, I can heare a difference, the noise level is falling, but that's about it.

Any bright ideas out there?

73 de LA2SL

Ulf

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