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ANTENTOP- 01- 2015, # 019 Insulation RX Transformer

In my case I mentioned that connecting on receiver Hallicrafters S-85 to the Coaxial Switch went to increasing noise at transceivers connected to the Switch. Insulation transformer helped me to remove the effect. Figure 4 shows design of the transformer. Figure 5 shows Hallicrafters S-85 on the bench.


Transformer was made with ferrite ring that I saved from an old Computer PIII. The ring had dimensions 32x16x6 (ODxIDxH). Permeability of the ring was unknown for me. Transformer had two identical inductors, each contained 10 turns coiled by wire in 0.5- mm diameter (24 AWG). The inductors were placed at opposite sides of the ferrite ring. Two lengths of coaxial cable in 20 cm were connected to the ring. The design was placed in plastic food box.


The transformer was installed between Coaxial Antenna Switch Protax CSR- 5G and coaxial cable going to receiver Hallicrafters S-85. Figure 6 shows the transformer inside opened food box. . Figure 7 shows the closed food box with insulation transformer. Figure 2 shows the closed food box sitting beside the Coaxial Antenna Switch.


The insulation transformer allows use the Hallicrafters S-85 without any noise influences to transceivers connected to the switch. Reception of the receiver was improved with the insulation transformer. Stations sound clearly with the transformer. I was mention that there were less noise and clicks in the receiver especially at lighting and pre storm period.



Figure 7 Closed Food Box with Insulation Transformer



Figure 5 Hallicrafters S-85



Figure 6 Insulation Transformer Inside Opened Food Box


I measured SWR when the transformer was connected to the 50- Ohm coaxial cable going from Beverage antenna and to MFJ-259B. SWR was in limit 3- 4 up to 4- MHz. Then SWR was sharply increased and reach 25 at 20- MHz. However, such high SWR does not hinder the reception. It is more important for the receiver is to cut low frequencies interferences going from static, lighting and some home and industrial equipment. The insulation transformer does it in good way.


73! I.G., va3znw

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Last Updated:

January 5, 2020 19:16