Various types of broad band VLF active antenna's have already been used with varying results and I thought it was time to make an improved narrow band version. I constructed a 1100mm square loop wound with 46 turns 1.5mm insulated wire and selected a pre-amp by testing coupled to the loop. The pre-amp is in fact part of a "Rugby Receiver" kit sold by Maplins but no longer in production and I am unable to find any information about what the receiver was used for but suspect that it was an accurate time source. I have drawn the circuit from the board and is shown on the right. I also experimented by resonating the loop but found that it would not cover the whole of the 8.700 to 9.100kHz allocation (without retuning) which was granted to the other operators.
Sub 9kHz - 1
9th November 2010 - 9kHz Receive Antenna Considerations.
The next stage will be to add a few more turns and construct a switched capacity unit to tune the loop at several points to allow it to cover the whole of the band in sections and possibly even broad band VLF by switching the capacity out for more general receiving. As you will see later in these pages the receive bandwidth was resolved.
Maplin’s Rugby receiver
Bandwidth of tuned receive loop.
Having done the rounds of most amateur radio frequencies from short wave listening
in the early 1950's and operating on bands from 1296MHz down to 136kHz using many
different modes my latest challenge is now sub-9kHz, Very Low Frequency (VLF).
A special licence is required for these frequencies titled "Special Research Permit"
(SRP) and an application to the UK communications authority Ofcom is required. On
successful granting of the SRP a change is made to the amateur radio licence conditions
in the form of a "Notice of Variation" (NoV). This is usually granted for 1 year
and if Ofcom allows the SRP to continue will be normally renewable each year.
Several enthusiasts of the now named "Dreamers Band" had successfully obtained their
NoV so I made the decision to make an application myself. I completed the form and
it went in the post on Saturday 6th November 2010.