Wideband preamplifier

Medium & long wave antenna discussion
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Joined: 07 Oct 2014 16:49

Wideband preamplifier

Post by daveB » 21 Feb 2018 14:56

This topic actually embraces LF to VHF - but never mind. On ebay there are numerous sellers offering a 30 dB 0.1 to 2 GHZ low noise pre-amplifier. One variant is shown below.
ina02186 pcb f1.jpg
I came across this whilst searching for an ina02186 MMIC to use in the shielded magnetic loop antenna designed by PA3GZK. I realised the board contained the same MMIC - ready made.

I've tested it out by mounting it in a small diecast box, using sma to f connector adapters.

Test 1 was powering it from 4 x AA alkaline batteries. A 10 dB attenuator was used on the output and it was fed from the OIRT dipole. The PA3GZK design has a 15 pF capacitor across the output - I has a 22 pF to hand.It looked to be perfectly stable in the range I could check - LF to DAB and then digital TV.

Test 2 was to add a bias tee - by connecting a 470 uH inductor between +VCC and the RF output. Feeding it through a standard TV masthead power unit gave good results - and confirmed that the pre-amp PSU contained a high pass filter as there was no LF/HF reception.

Test 3 was to build the simplest bias tee adapter - consisting of a 100nF blocking capacitor and a 470 uH inductor. This was fed by a small 12v linear psu (brick).

It should be noted that by the time you've bought the amplifier and the necessary sma to f-conector adapters and a diecast box the cost is similar to a Fringe Electronics Band II preamp.

But if you want a wideband preamp to cover 45-110 MHz then it is worth it.

As for the shielded magnetic loop antenaa - that is on hold. I had a hernia repair on Feb 12th and I am having to sit out the convalescing period. The operation and recovery went well - in at 09:00 -operation 9:50 to 10:50 - out at 13:30 and home by 14:00. I must not lift anything heavier than a up of drink until the end of the week. You have no idea how difficult it is not to forget. Even my overcoat is outside the weight limit! Total recovery about 8 weeks.

A friend put the following joke on a card. "How many hernia patients does it take to change a lightbulb? - None - you aren't supposed to stretch!!". I think that sums it up.

Mean time I am going through the tail end of the 2017 SpE logs and compiling a huge disc of old family photos.
SDRPlay, AirSpyMini, RTL dongles, SB920s, Yamaha TX930. 5 ele compact yagi on rotator at 18ft agl. FM5 facing east, FM5 facing south, FM3 facing NE, OIRT dipole, 3-ele Moxon vertical facing east.

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