Вычитал тут в рассылке о алиасах из УКВ ФМ диапазона:
Скрытый текстFor owners of the IC-7300 who operate in areas of high signal strength Band 2 FM transmissions, you may find some FM aliases in one or two places on the VHF bands.
I first became aware of FM music on about 70.7 MHz and this turned out to be from BBC Radio 3 on 92.1 MHz. I then discovered Radio 2 on 72.9 MHz which is aliasing from 89.1. MHz. The half way frequency between these two is about 81.35 MHz. I confirmed this by using a signal generator into the IC-7300 at those frequencies, as at first I thought the cause was outside the radio or antenna system etc. I cannot explain this particular aliasing relationship.
There is another alias which can be explained, this happens where signals are mirror imaged about half the ADC sampling rate. They are mirrored about 62.016 MHz.
So if I tune to 54.012 MHz I get GB3ANG that transmits on 70.020MHz (the FSK is reversed by this mirroring action). In addition BBC Radio 2 89.9 appears at 34.14 MHz and Radio 3 92.1 appears at 34.14 MHz.
The dual bandpass filter for those segments of the band covers 30-49.99 AND 54.01 - 69.99 MHz so the alias is much stronger once you tune out of the 50-54 MHz bandpass filter. The filter for 70 MHz covers 70.0- 74.8 MHz.
Fortunately those particular BBC stations don't appear to cause any problems within the normal weak signal parts of the bands here, but there is still the possibility that extra noise is being added.
I think it may be a good idea to add the simple mod kit that is now available from the dealers to break in to the IC-7300 receive antenna path so that extra bandpass filtering or notch filtering can be added to remove strong Band 2 FM signals before they reach the receiver of the IC-7300. I certainly plan to do something like that after my testing today with the sig generator.
The sort of signal strength that I was putting in to the receiver at Band 2 from my sig gen was about -43dBm and that is lower than some of the actual signal strengths I have seen from my antennas from my local BBC station at Blackhill which is LOS. http://www.gm4jjj.co.uk/preamp/index.html
David Anderson GM4JJJ
Having said that, I must add:
- yes, I hear FM Aliases on the range 30MHz to 34,5MHz
- I never found Aliases over 34,5MHZ (
- I have a few 36KW and 32KW FM broadcasting transmitters very close.... only 6km in direct line of sight.
As David explained very well the Aliases look like to be mirrored on 62.012MHz.
No need for bandpassfilters, as the Ham bands are never affected.
While I also observe FM stations (88 to 108 MHz) aliasing above 30 MHz, an ICE-brand low-pass filter that rolls off above 54 MHz removes the phantom signals. I also use an ICE 1.7 MHz high-pass filter to reduce the level of AM broadcast signals getting into the radio. Individual AM signals are as strong as -6 dBm from my 160-meter Marconi T antenna. The strongest is on 760 kHz, 50 KW daytime, but only 1 KW at night.
I have never observed aliasing in a ham band.
The only time I have observed the OVF light blink, assuming I generally keep the preamp(s) OFF, was during the ARRL 10 meter contest in December. I think it is likely a trucker, possibly running power, drive within 700 feet of my 5-element 10-meter monoband Yagi. Preamp 2 was ON at that time. (10 meter conditions were awful!) The OVF flashed for about 15 seconds. I don-t remember hearing any artifacts from the temporary overload.
Yes, same here with very strong, local Band II signals. A 70MHz bandpass filter in the 4m aerial lead is essential for me.
It is interesting that the aliasing audible above 30MHz cannot be removed by any amount of filtering. In fact, it's just as strong with only a power lead connected.
Так что кому важен чистый прием выше 30МГц т.н. "низового УКВ диапазона" - подключайте дополнительные ФНЧ или режекторные фильтры от УКВ ФМ вещания.
Отработал CW в RDXC на IC-7300, ещё раз убедился что сделал правильный выбор в его пользу.
Напряжение питания , + - ???
И ток на приём.???
У меня по азимуту 30 градусов (основная часть UA9 для меня) стоит подстанция ЛЭП железной дороги.
К сожалению треск круглосуточный...
Переключал 7300 и 7600 - заметил, что треск на 7300 воспринимается для ушей комфортнее.
При этом значения параметров эквалайзеров на обоих аппаратах - как говорится "FLAT"...
По чутью разницы не вижу.
Последний раз редактировалось Retiree; 20.03.2017 в 09:47.
Хороший трансивер, стоит этих денег
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