Difference between revisions of "70cms filters"
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There are plenty of designs available for 437 MHz filters: | There are plenty of designs available for 437 MHz filters: | ||
| − | ===450MHz | + | ===450MHz Low pass transmit Filter=== |
[http://www.minikits.com.au/electronic-kits/filter-kits/uhf-lowpass-filters/LPF7-450M Minikits in Australia] make a really good low pass filter which is ideal for use with the Portsdown or other 70cms DATV transmitters. | [http://www.minikits.com.au/electronic-kits/filter-kits/uhf-lowpass-filters/LPF7-450M Minikits in Australia] make a really good low pass filter which is ideal for use with the Portsdown or other 70cms DATV transmitters. | ||
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[[File:lpf7-450m-a-640x640.jpg|200px]] | [[File:lpf7-450m-a-640x640.jpg|200px]] | ||
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| + | ==Mini-Circuits RBP-440 Bandpass filter== | ||
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| + | Mini-Circuits make an excellent low power Bandpass filter - the [https://www.minicircuits.com/WebStore/dashboard.html?model=RBP-440%2B RBP-440 ]which passes 410-470MHz signals and is for mounting on a PCB. Very low insertion loss. About £16 each or try your luck with an application to their EZ Samples programme. | ||
===Simple inter-digital filter=== | ===Simple inter-digital filter=== | ||
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[[File:70cms 245 1.JPG|400px]] | [[File:70cms 245 1.JPG|400px]] | ||
| + | Paul Wade W1GHZ has published [http://www.w1ghz.org/filter/Combline_Filters_for_VHF_and_UHF.pdf combline filter designs] in tinplate and Hammond boxes. THe 432MHz design uses a 1590BB size box. These are more easily tunable than the Altoids tin filter by using 3 air trimmer capacitors. | ||
===Tuneable pass band filter=== | ===Tuneable pass band filter=== | ||
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The following suppliers sell built and tested units: | The following suppliers sell built and tested units: | ||
| − | + | ===eBay Chinese made 470MHz low pass filter=== | |
| + | [[File:70cm LPF.jpg|400px]] | ||
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| + | This small filter is available from here [http://www.ebay.co.uk/itm/131577649343 http://www.ebay.co.uk]for just £6 including post from Hong Kong. Insertion loss is only 0.3dB at 437MHz and the 2nd and 3rd harmonics of 70cm are attenuated by 45 and 60 dB respectively. See plot below: | ||
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| + | [[File:437mhz.jpg|400px]] | ||
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| + | This makes it suitable for use between the ADF4351 synthesiser and the Portsdown modulator to improve the constellation as well as the output of a driver stage up to about 1 watt. It would also be very useful to reduce overload from phone towers or broadcast TV if place in front of a preamp that has a wideband input. | ||
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| − | + | DG0VE used to supply reasonably priced filters for most amateur bands, but passed away a few years ago. | |
Latest revision as of 17:38, 17 April 2021
There are plenty of designs available for 437 MHz filters:
450MHz Low pass transmit Filter
Minikits in Australia make a really good low pass filter which is ideal for use with the Portsdown or other 70cms DATV transmitters.
As used by G4KLB, G8VPG and others.
Mini-Circuits RBP-440 Bandpass filter
Mini-Circuits make an excellent low power Bandpass filter - the RBP-440 which passes 410-470MHz signals and is for mounting on a PCB. Very low insertion loss. About £16 each or try your luck with an application to their EZ Samples programme.
Simple inter-digital filter
Design by F1DJO and F6GQM first published in CQ-TV 245
Paul Wade W1GHZ has published combline filter designs in tinplate and Hammond boxes. THe 432MHz design uses a 1590BB size box. These are more easily tunable than the Altoids tin filter by using 3 air trimmer capacitors.
Tuneable pass band filter
Tuneable passband filter design by Ian, G3KKD, with 2 MHz band pass and 30 dB attenuation 4 MHz away. (the full article is available in CQ-TV 228).
Built units
The following suppliers sell built and tested units:
eBay Chinese made 470MHz low pass filter
This small filter is available from here http://www.ebay.co.ukfor just £6 including post from Hong Kong. Insertion loss is only 0.3dB at 437MHz and the 2nd and 3rd harmonics of 70cm are attenuated by 45 and 60 dB respectively. See plot below:
This makes it suitable for use between the ADF4351 synthesiser and the Portsdown modulator to improve the constellation as well as the output of a driver stage up to about 1 watt. It would also be very useful to reduce overload from phone towers or broadcast TV if place in front of a preamp that has a wideband input.
DG0VE used to supply reasonably priced filters for most amateur bands, but passed away a few years ago.