Hello, since the responses of people from eastern Slovakia with the deaf Wouxun KG-UVD1 stations as long as they receive UHF are increasing, I will try to find out what is the cause of the "disruption". The malfunction occurs mainly when receiving the frequency of 446 MHz, but partially also when receiving frequencies in the vicinity of 439 MHz.
You will read in the article
What is the cause?
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).
On April 5, Towercom in Košice launched a DVB-T transmitter on K25 with a power of 16.9kW ERP from the Heringeš transmitter. From April 28, 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 on 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, exactly channel 25, which is a frequency from 502 to 510 MHz. The first intermediate frequency of this handle is 29.25MHz. The oscillator of the receiver for the 1st MF, for example, when receiving 446MHz, thus oscillates in KGUVD1P by 29.25MHz higher, which is 475.25. The mixer, however, processes a differential 446MHz but also a total 504.5MHz signal from the signal from the oscillator. The total signal should be suppressed by the input circuits, but the KGUVD1P has these poorly. 504.5 MHz lies directly in channel 25 (502-510 MHz). You might think, 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 of suppression at the mirror frequency, we get 12.3dBW, which can also be understood as 16W of interference at the desired frequency. It is now clear that the 16W assembled on the mixer from the DVB-T signal can be pushed by a useful signal of 0.5W from PMR the 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 in direct view of the DVB-T transmitter, or behind an obstacle preventing its reception or only at very short distances, sometimes only on the order of hundreds of meters.
So far, we have talked about listening at the frequency of 446MHz, but 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 detuning, because it is a two-band station.
Does it not apply to you?
Do you think that this problem with this station does not affect you in other regions? This may not be true, there are currently many requests for allocation of a local DVB-T multiplex at TUSR, 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 manifest itself:
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 the reception of 427.5-435.5 (direct FM channels and transmitter outputs in Hungary)
K24 494-502MHz may affect reception of 435.5-443.5 (outputs of FM converters)
K25 502-510MHz may affect reception 443.5-451.5 (PMR band)
K26 510-518MHz may affect 451.5-459.5 reception
K27 518-526MHz may affect 459.5-467.5 reception
K28 526-534MHz may affect 467.5-475.5 reception
Plans for the launch of full-scale DVB-T:
K21 – Zobor, Sitno, Levice, Šťúrovo, Nove Zámky
K24 – SNV-Grajnar, Poprad, Sp. Podhradie, Svit
K25 – KE-Heringeš, KE-Dubník, Prešov, Čaňa, Inovce-Poľana, Krompachy-Plejsy, Kr. Chlmec, Medzev, Moldava N.B, Obišovce, O. Matiašovce, Snina, Trebišov, Vihorlat, MI-Zalužice
K26 – Prievidza, Námestovo, Ružomberok
K27 – Kamzík, Borský Mikuláš, Brezová P.B., D. Streda, Trnava, Revúca, Rožňava, Slaveč
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, i.e. frequencies may or may not be assigned. I will select the most critical channels from our radio amateur point of view:
K23 – Liptovsky Mikuláš, D. Streda, Šamorín, V. Meder, D. Kubín,
K24 – Trenčín
In the vicinity of Bratislava, there is a risk that if the Austrian side decides to establish a DVB-T cover of its first mux broadcast on K24 somewhere above Hainburg, then we can discard the Chinese stations, but on the other hand, it is unlikely, as they have a built-up network and nothing in Bratislava and the surrounding area can start broadcasting due to a collision with Austria. However, K27 will be broadcasting in Bratislava, so forget about receiving professional services in the 459.5-467.5 band with this station and buy something else. If the coordination for K26 passes, which will probably pass after the shutdown of ČT1 from Páľava, then DVB-T will also be on K26 in BA...
I hope I have sufficiently explained why the majority of Chinese UHF stations in the East suddenly went deaf.
Tono OM1AEG