Problems with Wouxun KG-UVD1

Hi, as the responses of people from eastern Slovakia with the deaf stations Wouxun KG-UVD1 increase as they receive UHF, so I will try to find out what is the cause “disorders”. The malfunction occurs mainly when receiving the 446MHz frequency, but also partially when receiving frequencies in the vicinity 439 MHz.

The reason is the poor design of this handheld station, which is cheap and too sensitive, which is nice, but on the other hand, it has a very weak suppression of the mirror frequency at 440MHz by only 30dB (according to measurements on http://www.wouxun.us/Manuals/QSTReview.pdf).

5. April, Towercom in Košice launched a DVB-T transmitter on K25 with a power of 16.9kW ERP from the Heringeš transmitter. From 28. In April, Towercom launched a DVB-T transmitter on K25 with a power of 31.5 kW ERP from Dubník. And they plan to launch more DVB-T on K25 11.5. in Prešov, 12.5. in Kráľovský Chlmec, 12.5. in the Dream…

And what does DVB-T have to do with the current or future deafening of KGUVD1P in eastern Slovakia? Well, the channel 25, what is the frequency from 502 do 510 MHz. The first intermediate frequency of this handle is 29.25MHz. Receiver oscillator for 1. MF, for example, when receiving 446MHz, therefore oscillates 29.25MHz higher in KGUVD1P, What is 475,25. The mixer, however, processes a differential 446MHz but also a total 504.5MHz signal from the signal from the oscillator. The sum signal should be suppressed by the input circuits, however, KGUVD1P has these poorly. 504,5 MHz lies directly in the channel 25 (502-510 MHz). You might say, after all, 30dB suppression should be enough…

With a little math, we can convert 17kW from Heringeš to 42.3dBW. When we subtract from 42.3dBW 30dB suppression at the mirror frequency, we get 12.3dBW, which can also be understood as 16W interference at the desired frequency. Now it's clear, to push the 16W assembled on the mixer from the DVB-T signal with a useful signal of 0.5W from the PMR station that we only listen to on this station, will only be possible at a greater distance from the DVB-T transmitter, which can be up to tens of km with a direct view of the DVB-T transmitter, or behind an obstacle preventing its reception or only for very short distances, sometimes only on the order of hundreds of meters.

So far we have talked about listening at 446MHz, unfortunately, in the vicinity of DVB-T transmitters on K25, in units of km, there is also a slight deterioration of sensitivity due to the overload of the mixer in the range of 438-440MHz, where amateur radio converters have an output in the 70cm band. However, when receiving a local transmitter with a strong signal, it does not matter so much.

What is the solution? The simplest solution is to sell the radio or not to buy it. Another possible solution is to insert a sufficiently sharp tuning filter between the antenna and the radio, but only if we use an external antenna – I can't imagine such a filter on the handle, not to mention the possible detuning of the antenna with such an intermediate element. The filter should be debugging, because it is a two-band station.

You think, that in other regions this problem with this station does not concern you? It may not be true, at TUSR, there are currently many requests for the allocation of a local DVB-T multiplex and it is not excluded, that a DVB-T transmitter with a power of up to 5 kW will grow right in the middle of your housing estate. Therefore, I am attaching a table of DVB-T channels and their corresponding input frequencies, where the problem may occur:

K21 470-478MHz may affect 411.5-419.5MHz reception
K22 478-486MHz may affect 419.5-427.5MHz reception
K23 486-494MHz may affect reception 427,5-435,5 (direct FM channels and transmitter outputs in Hungary)
K24 494-502MHz may affect reception 435,5-443,5 (outputs of FM converters)
K25 502-510MHz may affect reception 443,5-451,5 (pasmo PMR)
K26 510-518MHz may affect reception 451,5-459,5
K27 518-526MHz may affect reception 459,5-467,5
K28 526-534MHz may affect reception 467,5-475,5

Plans to launch full-scale DVB-T:
K21 – Zobor, Small, Levice, Rudely, New Castles
K24 – SNV-Grajnar, Poprad, Sp. Podhradie, Svit
K25 – KE-Heringeš, KE-Dubnik, Prešov, Cana, Inovce-Poľana, Krompachy-Plejsy, Kr. Chlmec, Gap, Moldovan N.B, Obisovce, O. Matiašovce, Snina, Trebišov, To whirl around, MI-Zalužice
K26 – Prievidza, Squarely, Ružomberok
K27 – Chamois, Borský Mikuláš, Brezová P.B., D. Wednesday, Trnava, Roaring, Rožňava, Slavec
I drew the information from http://www.power.szm.com/dvb-t/dvb-t_03.xls

Requests for the allocation of a local MUX can be found on the TUSR website: http://www.teleoff.gov.sk/data/files/17881.xls, however, these are requests, so frequencies may or may not be assigned. I will select the most critical channels from our amateur radio point of view:
K23 – Liptovsky Mikulas, D. Wednesday, Shamorin, V. Bed, D. Cuban,
K24 – Trenčín

So there is a threat in the vicinity of Bratislava, that if the Austrian side decides to set up a DVB-T cover of its first mux broadcast on K24 somewhere above Hainburg, so we can discard the Chinese stations, but on the other side, it is unlikely, since they have a built-up network and nothing in Bratislava and the surrounding area can start broadcasting because of the collision with Austria. However, it will be broadcast on K27 in Bratislava, so to receive professional services in the band 459,5-467,5 forget about this station and buy something else. If the coordination for K26 passes, which will probably pass after turning off ČT1 from Páľava, so in BA there will be DVB-T also on K26…

I hope I have explained clearly enough why most of the Chinese UHF stations in the East suddenly went deaf.

OM1AEG tone