WHAT THE RMU DOES:
The RMU modifies 80m resonance of the 807-xx.
By using different values of capacitors inside of the RMU, we are able to place or change the resonance on 80m anywhere we wish, WITHOUT affecting resonance on other bands.
WHY IS THIS IMPORTANT ?
The 80/75m band is unique in that it is impossible to have a low SWR across the entire band, due to something called Fractional Bandwidth. Therefore the user must choose his/her favorite resonante frequency and adjust the antenna for that. On normal dipoles, "adjust" means adjust the length.
BUT... with an OCFD antenna, adjusting the antenna's length on 80m ultimately affects its resonance on ALL higher harmonic bands, often moving resonance upwards and outside of the ham band. So length adjustment is a bad idea! DO NOT CHANGE THE LENGTH OF ANY AERIAL-51 OCFD ANTENNA!
By moving 80m resonance with an RMU, we are able to adjust 80m resonance without affecting resonance on the higher bands. In theory, we can place the frequency of minimum SWR (SWRmin) anywhere we wish . . . by adjusting the value of the capacitors inside of the RMU.
In addition, by swapping the RMU for one with a different value, users are able to change the SWRmin as desired (i.e., use an RMU-CW for a CW contest and an RMU-EU or RMU-US for an SSB contest).
THIS IS A UNIQUE FEATURE OF THE RMU!
and the Aerial-51 807-xx antennas.
NOTE: The 'Frequency of Minimum SWR' shown for each RMU above is only the approximately frequency. The actual frequency may vary by +/- 25 kHz due to manufacturing tolerance of the capacitors, height of antenna above ground, and consistancy of the earth below it, which varies from one QTH to the next.
CURRENTLY there is very high demand of Power-SMD Capacitors,
especially due to the high demand in the Solar Industry.
As a result, most values of capacitors are not readily available.
Suppliers have set minimum quantities for orders, usually 1000 pieces, and even then there is a long lead time.
With the capacitors that Spiderbeam currently has (in large quantity) in stock, they are only able to set resonance within a range of about 3.650 to 3.720 MHz.
The RMUs can be exchanged at a later date, or users can build their own replacement RMU, setting resonance anywhere they like.
Contact Spiderbeam for more information on this.