Improving ULR FM reception

1. Whip (20/115 cm). 2. 3,5 mm jack splitter. 3. BNC/3,5 jack adapter. 4. UL Pocket radio.

Often I get surprised when I listen to the FM Band with my autoradio. It has no bandwidth options, no filters, but sensitivity and selectivity are much better than most of the well-know portables. Mine is inserted into the Skoda console so I have no way to know who manufactured it, the brand/model or its tech specifications. Most of the times I wonder why other portable firmwares does not include, for instance, similar choices like the high speed decoding RDS info. Then I thought… Will be my ULR Sangean DT-800 up to the task?

SKODA Autoradio & Sangean DT-800

An autoradio like mine (SKODA Spaceback car) decodes RDS and hears weak signals at once. It is part of a well balanced system: receiver-feedline and rubber antenna on the metallic car roof. My pocket ultralight radios use the earphone cable as an aerial, so even being very good receivers, the antenna is far to be reliable with tricky and changing reception as it depends on the cable position at every moment. Uhmmm! I needed to find a better way to listen using my small toys.

In the shack I had some whips with male BNC and PL-359 connectors, but the Pocket ULR has a 3,5 mm female plug-in, so I found a «female BNC > male jack 3,5 mm» adapter and connected the whip. I chose a telescopic antenna 20/115 cm long folded/unfolded to test the Sangean DT-800T versus the SKODA autoradio, focused on the BOTB from 87,5 to 91,5 MHz. When a long whip is used some unwanted effects come into the scene. The first is related with audio; connecting the whip the sound must be heard via the small speaker so don’t forget to choose a quiet environment not to miss weak stations. The second one is pure physics; due to the whip length, the ULR 3,5 mm female plug-in gets extra strain and that could damage the inner weldings, so extra care must be kept in mind at any time.

3,5 mm jacks splitter.

Finally I found a solution to avoid that stress on the female plug-in. I chose a 3,5 mm splitter (one male, two females) so both the whip and the earphones could be connected together. This allowed the choice to listen carefully to weak signals with ear devices, something essential to identify distant stations.

The use of a longer whip connected to the earphones plug-in expands pocket ULRs possibilities allowing better chances for FM DXing. This solution is suitable for different models and I checked this successfully with my Sangean DT-250, DT-800 and CC Pocket. Perhaps a better option for the whip connection would be to provide a longer cable and then place the aerial on a better spot when operating on portable, even FM rabbits could be then used.

Back to the UL pocket radio Sangean DT-800, the comparison with the autoradio was very satisfying. With this long 115 cm whip I checked the FM BOTB founding 24 stations with my SKODA autoradio and 22 with the DT-800. With powerful stations, signal levels and RDS decodings were identical, and I found differences in 14 stations. Full results are showed in the table below:

TestSangean DT-800Autoradio SKODA
Stations received2224
Received PS codes 1114
Furthest (205 km) RNE-R3 Boal, AST (10 kW)SIO 0SIO222
87,5 Radio 4G (? kW, 62 km)SIO211SIO323
87,7 R. Fútbol (1,4 kW, 34 km)SIO555SIO555
87,8 OCR Burgos (0,5 kW, 79 km)SIO 0SIO211
87,9 RNE Clásica Llanera (10 kW, 128 km)SIO322SIO444
88,1 R. Martínez (? KW, 48 km)SIO444SIO555
88,2 RNE Radio 3 Boal (10 kW, 205 km)SIO 0SIO222
88,3 Los 40 Gijón (4 kw, 100 km)SIO444SIO555
88,4 Cadena 100 Llen (6 kW, 48 km)SIO454SIO555
88,7 Radio HM Ibio (1 kW, 13 km)SIO555SIO555
88,8 RNE R. Nacional AST (2 kW, 60 km)SIO332SIO433
89,0 RNE R. Nacional CANT (10 kW, 49 km)SIO555SIO555
89,1 COPE Avilés (4 kW, 134 km)SIO222SIO222
89,4 RNE R5 Ibio (5 kW, 22 km)SIO555SIO555
89,6 Distinta FM Llen (? kW, 33 km)SIO555SIO555
89,8 89.8 FM Llen (? kW, 34 km)SIO354SIO555
89,9 RNE R5 Gijón (20 kW, 115 km)SIO222SIO433
90,1 Onda Occidental (0,1 kW, 16 km)SIO555SIO555
90,3 Dial Santander (6 kW, 48 km)SIO444SIO555
90,5 RNE Clásica Puentenansa (1 kW, 17 km)SIO121SIO322
90,6 Radio Mix Llen (? kW, 48 km)SIO555SIO555
90,7 Rock FM Avilés (4 kW, 127 km)SIO333SIO554
90,9 Los 40 Santander (6 kW, 48 km)SIO555SIO555
91,3 Radio Líder Llen (? kW, 42 km)SIO455SIO555
91,5 SER Oriente Llanes (1,2 kW, 29 km)SIO555SIO555
The ‘long whip’.

The Sangean DT-800 showed a good overall behaviour. Selectivity is marginally better in the Skoda autoradio even with 100 kHz steps. The squelch level mutes every weak station when a more powerful one takes into action, so perhaps some of these could disguise weak ones. However the pocket UL Sangean allows 50/10 kHz steps so, this advantage allows that almost every weak station -even affected by strong splatter-, could actually be tuned in slightly up or down its nominal frequency. On the other side, when signals were not very strong, the overall SIO showed on the autoradio was always higher socred as showed in the table above.

This test gave me wings and one of these days I will test the three pocket ULR that I own: the Sangean DT-800, the Sangean DT-250 and the CC Pocket on the FM side under identical conditions as showed here: same receiving spot using the long whip and checking the same spectrum range. I will bring it here!

IberiaDX ©2021

2 comentarios en “Improving ULR FM reception

    • I do not have LW/MW band option in the car radio. Regarding to FM listening I do not think that replacing the standard antenna add any benefits, as the receiver is limited by its selectivity. Sensitivity is outstanding even with the short rubber duck roof antenna given by Skoda. Saludos.

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