Wednesday, 26 November 2008

MKARS 80m tcvr

Bought a kit at Leicester Rally and will be a kit for Xmas holidays.

The reverse tuning is a bit odd which is probably what interested me.

As my QTH is only c40 miles East of MKARS/Betchley Park I expect I might visit once operational.

I took all the parts out once arrived home, before dutifully putting it into one of the clear boxes I use for storing build projects in the shack. So far I can see I might experiment with a slightly larger case using an air spaced variable (another Leicester purchase) and a reduction drive for tuning or might try the varicap mod with a 10 turn pot (bought a whole box of various values both recycled and new at GQRP rally), definitely will add an in case battery holder which will also be used by rechargable batteries, a little L match ATU so self contained for /P, I find the W3EDP antenna works well for 80m and finally will have to paint it some luminous/gawdy colour scheme so a trip to B&Q to see what colour spray enamel paints are available is needed.

After spending last year in HB9 I discovered the benfit of using lock 'n' lock boxes for homebrew in cold & wet /P conditions so might investigate using one possibly as the enclosure not just transport in a rucksack/bicycle pannier.

Thursday, 20 November 2008


Bit of an abscence for almost a month.... reason is I had a job/work to do so radio took a back seat for a bit.

Just picked up on the discussions about using the TA7358 as an alternative to the SE/NE602 as a mixer which I am all in favour of as the 602 are becoming very expensive.

Ordered a number from Peter at Jabdog and once they arrive will start to look at them in circuits.

One advanced option is here:

The text in Russian is:

Приемник прямого преобразования для диапазона 7MHz
Cosy MUTO, JH5ESM (вольный перевод Валерия, RW3DKB)

Этот приемник - разработка для Технического Симпозиума ARRL 1999г в Кагава (Япония). Входная ИС используется для формирования внешних цепей FM-приемников и содержит каскады УВЧ/смеситель/гетеродин. Для питания достаточно 3 вольт - только 2 батарейки типа АА.
Описание Схемы.
Рис. 1 показывает оригинальную схематику приемника.
Рис.1 Оригинальная схематика приемника.

Микросхема TA7358AP содержит в себе все входные каскады для FM приемника в одном корпусе. Ножки с 1 по 3 - это цепи каскада УВЧ, с 4 по 6 - это цепи двойного балансного смесителя Гилберта (Gilbert DBM cell) и с 7 по 9 - выводы транзистора гетеродина.
Полный диапазон приемника оценен как 90dB. Дополнительный звуковой усилитель потребовался для получения громкоговорящего приема.
Звуковые Колебания.
Возникают паразитные звуковые эффекты, когда Вы делаете громче регулятор громкости. Это вызвано обратной связью через линию питания. Для их устранения необходимо модернизировать схему. В частности ввести в нее развязывающие цепочки по питанию каскадов.
Переделанная схема представлена на Рис.2.

Если напряжение постоянного тока через резистор 1 кОм больше чем 0.6 V, его номинал должен быть уменьшен, чтобы избежать запирания внутренних диодов в TA7358.

The English translation is:

Direct conversion receiver for the band 7MHz Cosy MUTO, JH5ESM (loose translation of Valery, RW3DKB) Introduction. This receiver - development for the Technical Symposium ARRL 1999 in Kagawa (Japan). Home IS used to form external circuits FM-receivers and contains cascades UHF / mixer / oscillator. For a 3-volt power supply - only 2 batteries type AA. Description of the Scheme. Fig. 1 shows the original shematiku receiver. Fig.1 The original shematika receiver. TA7358AP chip contains all the input cascades to the FM receiver in one case. Motor from 1 to 3 - this cascade of UHF supply chain, from 4 to 6 - this chain of double balanced mixer Gilbert (Gilbert DBM cell) and from 7 to 9 - the findings of transistors heterodyne. Full range of the receiver rated as 90dB. Additional audio amplifier required to obtain loudspeaker reception. Sound Fluctuations. There parasitic sound effects when you make a louder volume. This is due to feedback through the power line. To eliminate the need to modernize the scheme. In particular, to enter into it razvyazyvayuschie chain of food cascades. Reworked diagram Pic.2 represented at. Note. If the voltage constant current through the resistor 1 kOhm more than 0.6 V, its face value should be reduced to avoid locking the internal diodes in TA7358.