Vertical Doublet Antenna for Tight Spaces, bands 20-10m (40-10m)

I wanted to write about the most succesful apartment antenna I have used thus far. It is the vertical doublet. A vertical doublet is a symmetrical antenna which is basically a dipole on some frequency fed with a low loss open feeder line. The feeder line section tunes the antenna.

The antenna has given me excellent results on the bands and it really shines on 10m where it is a full wave vertical dipole. The radiation angle for maximum gain is around 12 degrees on 10m. The most distant operator I have heard on 10m was some guy near Los Angeles during sunset in Finland. The most distant QSO was to Arkansas. On 10m the DX operators have commented that the antenna really does work for low angle radiation and testing with the locals also confirms it.

By playing with a model in MMANA you can see how adjusting the two variables which are 1) radiating wire length 2) open feeder length change the tuning. I have managed to tune the antenna so that on 10m and 17m it does not need a tuner. My setup is following:

RADIO--TUNER---COAX----1:1BALUN===450 Ohm line, 6.6 m or so===5m wire up, 4.7 m wire down


The structure looks like the letter T which is tilted 90 degrees to the side. The lower wire facing the earth needs to be a little shorter than the wire facing the sky because it couples to the earth and thus gets the antenna a bit out of balance. The feed line must be routed in a 90 degree angle so that it does not interact with the radiating elements. The coax cable between the balun and tuner should be as short as possible but the open feeder should start a couple of meters away from any structure to decrease noise pick up.  I will post the antenna model for MMANA below.

*
14.15
***Wires***
5
0.0,    0.0,    0.02,   0.0,    0.0,    5.12,   8.000e-04,      -1
0.0,    0.0,    0.0,    0.0,    0.0,    -5.01,  8.000e-04,      -1
0.0,    0.0,    0.0,    0.0,    7.85,   0.0,    8.000e-04,      -1
0.0,    0.0,    0.02,   0.0,    7.85,   0.02,   8.000e-04,      -1
0.0,    7.85,   0.0,    0.0,    7.85,   0.02,   8.000e-04,      -1
***Source***
1,      0
w5c,    0.0,    1.0
***Load***
0,      0
***Segmentation***
800,    80,     2.0,    2
***G/H/M/R/AzEl/X***
2,      5.2,    0,      50.0,   120,    60,     0.0


A link to the model here: http://koti.kapsi.fi/~mortal/vert_doublet.maa

Tecsun PL-660 DRM Mod

This is a DRM mod I found from the Internet. There is a video on youtube where it is used:

http://www.youtube.com/watch?v=vyYrQSBt_4Q

This is the picture of the mod stored here:

If I do the mod some day I will write about the results but I posted it here so that the modification doesn't go missing from the Internet.

de OH6GFR

Testing the Tecsun PL-660 on SSB ham bands

I decided to test the Tecsun PL-660 by using my outdoor vertical doublet antenna coax center conductor connected to the antenna, results:


http://www.youtube.com/watch?v=BSBhB1lML58 12m qso, low signal level but readable

http://www.youtube.com/watch?v=b8BDj46hHs0 40m Finnish net

http://www.youtube.com/watch?v=31XtuIUHjs0 80m Finnish net with wide filter setting

All these results are after the squelch mod which improved low signal handling significantly.

The new Tecsun PL-660 and the Squelch Mod

Finally I got the Tecsun PL-660 from China. There is a lot of talk about the squelch mod because low but readable signals cause the audio go out. I will publish a short instruction to do the mod:


1. Open all the screws
2. Get access to the back side of the radio where the PLL circuit is (under metal)
3. Desolder the metallic cover
4. Find the SMD transistor and short the two leads as shown here in this picture (found and archived here):

Here are some results from the mod before/after

before:

http://www.youtube.com/watch?v=BsHzli1WmYM

after:

http://www.youtube.com/watch?v=7HLT0DiY0Q4 80m local net from my tecsun


Search youtube for tecsun pl-660 squelch mod for more videos.


de OH6GFR

UV-5R New Stock Antenna

If you are searching for a good antenna for the Baofeng UV-5R then check this:

http://www.ebay.com/itm/Genuine-Baofeng-DualBand-Original-Antenna-for-UV-5R-UV-5RA-UV-5RB-UV-5RC-UV-5RE-/251306159400?pt=UK_Mobile_Phones_Communication_Radio_Antennas&hash=item3a8303ad28

cheaper:

http://www.ebay.com/itm/Genuine-Baofeng-DualBand-Original-Antenna-for-UV-5R-UV-5RA-UV-5RB-UV-5RC-UV-5RE-/161068205757?pt=AU_Electronics_Radio_Equipment&hash=item258069c6bd


The antenna is SIGNIFICANTLY better (SWR & power output) than the old stock antenna which is significantly shorter also:

http://www.ebay.com/itm/GENUINE-ORIGINAL-BAOFENG-SMA-FEMALE-DUAL-BAND-ANTENNA-AERIAL-UV-5R-UV-5RA-UV5R-/130984953020?pt=UK_Mobile_Phones_Communication_Radio_Antennas&hash=item1e7f4fc4bc


The antenna has very good performance on 2 m and 70 cm and it seems that Baofeng has really tuned this antenna for the ham bands. Added bonus is the lower swr and lesser heat.