Indoor antenna

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NH7SR
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Last seen: 10 months 3 weeks ago
Joined: 2010/04/07 - 07:18
Indoor antenna

Managed to get to the hardware store today to buy materials. My 2nd floor bedroom shack is now graced with a 6' indoor vertical using 1/2" hard drawn copper pipe for the antenna. Matching to the input of the SDR-IQ with about 24 turns closewound #20 plastic insulated hookup wire wound on 1/2" schedule 40 PVC pipe immediately below the copper pipe. The whole thing supported by a discarded stand fan base.

Ground reference is provided by a couple of scrap wire radials one of which is close to 24' long. This is augmented by a connection to the aluminum window frame that runs the length of the apartment (about 35'). Tomorrow I will purchase some 16 gauge wire to create a better radial system. I will probably only be able to properly accommodate only 2 radials.

A test with my Autek VA1 analyzer shows VSWR at 1.5/1 on 10.140MHz. With a bit of judicious sanding and tightening of connections Spectravue reports the noise floor pleasingly low at -120dB RMS. This is only 3dB noisier than my 135' outdoor long wire at 35' height with L-net tuner. There is, of course, a hit on signal pickup but less than I anticipated. Using W1CDO's signal from ~2600 miles distance for comparison the indoor vertical is only 10dB down compared to the outdoor longwire. Much better than I thought it would be... I was anticipating a roughly 24dB hit on SNR but it appears to be just a bit more than half that figure.

Still to try is a tophat which I suspect will only increase the noise and also a variable cap between the copper pipe and loading coil which will allow easy tuning and may offset the potential noise increase due to use of a tophat. Series resonating the radials may also prove beneficial although that will have to wait until I can order some more variable caps.

The new antenna as it stands will be left running tonight. Crossing my fingers and hoping that I will see a few more signals from the US mainland and perhaps from Japan and/or down under.

73 es 72,

'Bear' NH7SR in urban Honolulu