= HF8V = / = SP8WJT = / = SP0106RZ =
HF-17135
PROJECT: HF-17135
DESCRIPTION: Multiband receiver (broadcasting)
TYPE: PR-804
BRAND: ? (chinese production)
STATUS: f -> u
PROJECT START DATE: near 2012
LOCALISATION:
DOCUMENTATION: B-8 page 38 (PCB drawings, measurnments)
TPD: TPD57135
BANDS: MF, SW1-SW6, VHF
FREQUENCY: HF: 5.5 - 29.9 MHz, VHF (not measured)
MODULATION: AM, WFM
SUPPLY VOLTAGE: 3V
SUPPLY CURRENT: 4.7 mA
HARDWARE VERSION: 1.02
I had some fun making this receiver working again. I remember well 1980's when shortwave bands full of broadcasting stations were fascinating place, but today there are very few signals comparing to these days... But still I like listerning from time to time. Especially our Chinese Comrades are well represented today
(I like more their national stations even if I don't understand chinese because english service sounds little bit too much Propaganda style for me). Selectivity and image rejection of such kind of receivers are very bad of course, but please remember Comrades that good operator can work even on very bad receivers while capitalistic operators working bad on very expensive receivers :)) That you can hear on amateur radio bands. More seriously speaking HF preselector like HF-2836 can help with image rejection little bit.
Those who blame CXA1691 for bad performance are wrong. In this particular receiver RF input filters are a joke and additional wideband RF amplifier on S9018 only worsen things... So, very bad and cheap construction is a problem, not CXA1691 itself. In result always no image rejecting exists and reciprocal mixing is normal thing, for example I heard local CB station in 6 MHz band because probably 27 MHz signal was mixed with 21 MHz broadcast station... Well, that can be interesting too... You are also always receiving two frequencies 930 kHz spaced on such receivers. In 1930s when HF broadcasting bands were created they wisely made it below 930 kHz wide for that reason (at that time it was difficult to obtain good image rejecton near 30 MHz even in high class communication receivers), but at that time frequencies around broadcasting bands were full of high power fixed service stations (called 'radio service' in telecommunication jargon). Today such receivers can work because HF bands are almost empty. But still you are receiving noise from another image frequency even if no interference is present.
I received this device as main board with some elements destroyed but I repaired it and measured. Nice things is that HF is in 6 bands what means that analog tuning is not so bad on such wide range.
Measured bands:
1/ MF
2/ 5.5 - 8.1 MHz
3/ 9.1 - 13 MHz
4/ 11 - 16.1 MHz
5/ 12.7 - 17.1 MHz
6/ 18 - 26.6 MHz
7/ 21.2 - 29.9 MHz
8/ VHF
Minimal supply voltage: 1.45 V (with degraded sensivity but strong stations can be received clearly)
This low supply voltage and low current is interesting factor for using this recever in the portable usage. When voltage grows to 1.8 V sensivity is almost good.
I decided to give another life for that circuit, with few objectives in mind:
1/ Low power and supply voltage technology must be continued
2/ VFO must be removed from PCB and properly screened (VFO paths goes through half of PCB radiating and producing 'birds' and reciprocal mixing)
3/ VFO tuning changed from awfull Ducati gang tuning capacitor to varactor voltage tuning - usually I don't like voltage tuning, but here it can be better. I can create more bands and two or three potentiometers can be used for fine tunig. Radio without fine tuning is a full disaster - it can annoying user.
3/ PLL instead of VFO ? Only with low power CKT and without noises - so maybe later.
4/ Metal case for screening
5/ Preselector on the input - I decided to made similiar version of HF-2836 but in budget version, with no toroid HF cores but with axial inductors and with other transistor than J310. This should be efficient for HF broadcasting. Operation of radio with preselector is little bit 'complicated' - maybe for that reason it is not used in consumer products, but for me as a radioamateur it is normal that radio have many tuning knobs... Tuning of course can be done by microprocessor but that colliding with point 1.
There is also another receiver on CXA1691 HF-17897 but this will be used for parts and experiments.
Sources:
[1] CXA1691 datasheet
Prefix 17
HF Register
Microcontrollers in my constructions and external equipment
UC Database - my CPU collection
Electronics
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