This page aims to collect and show all the experiences that I have had working with Indoor Antennas. Therefore this page is an "alive document" where I will be including new stuff whenever new tests are performed.There are several contributions, in all of them I am pointing out the original author or the possible contributions in order to help me to put up and running the project.
There are some of them tested by myself, and other even though are included here as well they are still in test phase .In most of the cases, and due to the fact that the antennas have been used in portable QTH, it has not been possible to present the results from the scientific perspective because the lack of appropriate tools to measure the real performance of the antenna. In such cases you could find not too strict comments based sometimes in feelings more than real numbers (RST received from other colleagues, level of signals during SWL process, etc.) I hope no one will be bothered by that, I am still trying to incorporate as much accuracy as possible.
DCTL (Distributed Capacity Twisted
Loop)
Theory and Construction
A DCTL is a Loop antenna with the shape of a Delta Inverted built with 300 ohms TV parallel wire that uses the capacitance created as a consequence of being parallel to perform a 1/8 wave length antenna. The original design comes from Jim McLelland, WA6QBU (his original articles were published in 73 Magazine Sept93 and y Apr 94).
I collected some comments and explanations from Bob Follet AB7ST in the QRP-L mailing list and from the site The Curmudgeon's Hobbies -- The Ham Radio Page from Martin D. Watt (the link was provided by IV3ZBL, Andrea Zorzini another apartment inhabitant like me and that share some experiences with antennas for reduced space)
In the picture it can be shown how the DCTL was built in my QTH OH2(Helsinki).
Formulae used
=================
Total Length in meters- Lt (Ll + Lz) = 39,624 / F(MHz)
Adapter short-circuited in cm.(Lz) = 822,96 / [(2xF(MHz))-2]
Loop Length- Ll = Lt-Lz
Open Adapter (Lc) = 731,52 x (1 / [F(MHz)/2]**2).
In the following pictures the details of the construction can be seen:
and this is the extended version of the center of the DCTL where you can see better how the connections are made:
I used it for 40m. (centeres in 7,020 MHz) therefore the antenna(Lt) had a length of 5,64 meters, where Lz = 68,35 cm. and Lc =59,37 cm. You have to keep in mind that increasing the length of Lc the resonance frequency will be reduced.
With this kind of construction what we are doing is to twist the wire only at connection level.
You can use a balun 6:1 if you have a tuner with an inout unbalanced of 50 ohmios or if the inout is balanced the connection can be made directly(as I did).
Test Performed
QTH in OH2
My first experience with this kind of antenna was in OH2 (Helsinki) where I was living in an apartment and I was looking for an appropriate antenne to make radio( see how my working conditions were at my QTHMy trips OH2 ). I built it (basically with the help of Bob Follet AB7ST)suspended from the ceiling of my apartment using a long wooden stick that I found in a corner of my apartment and with the aim of keeping the structure rigid I used a kitchen wooden made tool tied in the bottom of the antenna. It was placed in several places for testing purposed: in front of a window (with wood frames) and in front of an indoor wall of the apartment.
The rig used was my RIG Howes (DXR20 and TX2000 ) and the output power was 5W. Working QRG 7.0-7.40 Mhz.
In reception mode the signals were quite good, above all if the polarization was horizontal.Signals from DL came with S 9+10. The problem that I suffered during my whole staying in Helsinki was the high level of electric noise that sometimes it reached S9+20 and in such case I just switched off my rig and started to read a good book.
In tranmission mode the results were worse than in reception and as result I was not able to make any full QSO. Some stations were listening me (UR, UY, EW) but the signal was so poor that even they could not to copy my call sign. I understand that the losses were considerable although, unfortunately, I was not able to measure the real losses to understand the reasons.
In general, and althouh the Bob Follet's comments and from other colleagues that pointed out the quite good performance of such kind of antenna, I think that the conditions were quite different.Most likely the tests performed by my USA colleagues were in a building of wooden made attics, however in Europe it is very difficult to find such kind of building nowadays that could ease to get such good results. In any case I am going to follow testing this antenna in other places to find the best tuning.
Theory and Construction
The folded dipole is one of the most well-known antennas due to its high-efficiency and simplicity.
Tests Performed
QTH in OH2
The rig used was my RIG Howes (DXR20 and TX2000 ) and the output power was 5W. Working QRG 7.0-7.40 Mhz. With this antenna was impossible to make any QSO from my QTH in Helsinki. The reception signals were good but as it crossed all the apartment I am afraid that the losses were considerable due to the interferences with some electrical machines that were closed to one of its legs.However I will follow testing it in other environments.
Theory and Construction
To fit it in the walls I had to use padded sticker with two faces used typically in the windows for protecting the indoor of the apartments in winter and avoiding losses of the heating system.
Tests Performed
QTH in OH2
The rig used was my RIG Howes (DXR20 and TX2000 ) and the output power was 5W. Working QRG 7.0-7.40 Mhz.
Theory and Construction
This antenna was recommended to me by G4DGX. It seems that was published in the well-known "Short Wave Magazine", magazine specialized in SWL, the article was "Espionnage Antennas" and was based on a UK RAF book unclassified (I'm still looking for that article to see more details of the antenna).
The following picture shows the installation of the antenna in the dinning-room of my apartment in Helsinki.
The material used was parallel wire of 300 ohms with a length of 1/4 wavelength, in my case was 10,676m that lifted up on the wall 'til the ceiling and finished in the opposite wall. Over there the endings were short-cut closing the circuit.The ending closer to the rig was connected to a tuner with input balanced (in my case was a Z-match built by my friend EA5TX (r.i.p))
To fit it in the walls I had to use padded sticker with two faces used typically in the windows for protecting the indoor of the apartments in winter and avoiding losses of the heating system.
Another alternative is to use a simple wire, not parallel, and folded in the opposite wall in such case a high radiation angle is obtained or folded in the ceiling where in such case a low radiation angle is obtained.
The tuning was done quite straightforward and the signals were really good (599+9dB or even 500+10dB).
Tests Performed
QTH in OH2
The rig used was my RIG Howes (DXR20 and TX2000 ) and the output power was 5W. Working QRG 7.0-7.40 Mhz.
The QSOs made with this antenna were significative since it was my last week in Helsinki (always happens this). The contacts were:
| QRA | RST received | RST sent |
| UR3LFO | 599 | 599 |
| UY2VM | 559 | 599 |
| RZ3TYU | 559 | 599 |
| SM7TOG | 339 | 599 |
| UA4SMM | 559 | 599 |
In my research of Indoor Antennas I went to several mailing lists such asQRP-L, antennas@qth.com and G-QRP and I received very impressive alternatives from several collegues to install an indoor antenna: good and cheap. It is very important to keep in mind that the good working of the antenna depends upon its construction as well as the boundary conditions(more important the former that the first one because in the indoor of an apartment there are several elements such as tubes, electrical installations that will have influence in the level of losses and in the radiation resistence).
I am going to chat a little bit about the alternatives that were sent to me by e-mail and as soon as I wil lhave some time and chance I will test them and I will include in this site the results:
Aluminium Paper Dipole based on
Done basically with aluminium paper used in the kitchen for storing food in the refrigerator. You have to use two rolls and fixed on the ceiling with staples. The feede point can be connected to the feed line by means metallic pegs and with the idea of avoiding to use heavy wire you can use parallel wire of 300 ohms.
Water DrainPipe
In some houses you can find pipes for draining water whenever rains made by copper. You can connect the baseline to the tuner with an input of long wire.
