{"id":5565,"date":"2023-02-26T20:00:48","date_gmt":"2023-02-27T00:00:48","guid":{"rendered":"http:\/\/www.engineeringradio.us\/blog\/?p=5565"},"modified":"2023-02-26T20:00:50","modified_gmt":"2023-02-27T00:00:50","slug":"hf-vhf-receiver-diplexer","status":"publish","type":"post","link":"https:\/\/www.engineeringradio.us\/blog\/2023\/02\/hf-vhf-receiver-diplexer\/","title":{"rendered":"HF VHF receiver diplexer"},"content":{"rendered":"

UPDATE and bump<\/strong>:\u00a0 This post is from eleven years ago, but I have been working on an SDR project using one of the RTL- 2832 chips.\u00a0 I had to make two more of these units, so the prices and part numbers have been updated.<\/p>\n

I have acquired one of those broad-banded software-defined radios, an Icom PCR-1000 to be precise, and all is well.\u00a0 I am enjoying listening to various MF, HF and VHF radio stations.\u00a0 However, there is a slight problem.\u00a0 Very slight, almost too small to even mention, more of an inconvenience than a problem.\u00a0 Still, if I am being inconvenienced, then others are too.\u00a0 This issue is with the antennas.\u00a0 My K9AY antenna works wonderfully from 500 KHz to 25 MHz or so.\u00a0 My discone antenna works wonderfully from about 30 MHz all the way up to about 1 GHz.\u00a0 In order to enjoy the full range of the receiver, I need to switch antennas.\u00a0 I have a small switch on my desktop, but it seems inconvenient to reach over and switch it when going from the AM band to the FM band or something similar.\u00a0 Therefore, I have decided that I need an HF\/VHF receiver diplexer.\u00a0 One would think that such hardware is ready-made for such instances.\u00a0\u00a0 However, nothing I could find commercially would do the trick.<\/p>\n

Thus, since I could not buy one, I decided to build one to add to my collection of receiver doo-dads and nick knacks.\u00a0 The design is relatively easy, a back-to-back low pass\/high pass filter system with a 50-ohm impedance throughout.\u00a0 Something with a sharp cut-off around 30 MHz or so:<\/p>\n

\"Diplexor<\/a>
Diplexor plot<\/figcaption><\/figure>\n

Looks pretty good, 5th order Chebyshev filter, perhaps .1 dB ripple in the pass bands if well made.\u00a0 Schematically:<\/p>\n

\"HF<\/a>
HF VHF diplexor schematic diagram<\/figcaption><\/figure>\n

Then it comes down to the building. Since this is going to be used in the UHF range, care and attention needs to be paid to the layout of the components and the design of the circuit board.\u00a0 Some of those capacitance values are not standard, however, by using two capacitors in parallel, one can get pretty close.\u00a0 Since this is going to be used for receiving only, I may be splitting hairs, however, I have found that well-designed and built equipment is worth the extra effort.<\/p>\n

The board layout looks like this:<\/p>\n

\"HF<\/a>
HF VHF receiver diplexer board<\/figcaption><\/figure>\n

I tried to keep the traces as close to 50 Ohm impedance as possible.<\/p>\n

As one may be able to discern, C2 and C3 are in parallel to make 192 PF, C5 and C6 are in parallel to make 60 PF, and C7 and C8 are in parallel to make 163 PF.<\/p>\n

The input and output RF connectors are whatever the builder wants to use, however, I would recommend at least BNC or type N for the VHF\/UHF side.\u00a0 My unit has all type BNC female connectors.\u00a0\u00a0 Parts list:<\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n
Nomenclature<\/td>\nValue<\/td>\nMouser number<\/td>\nCost (USD)<\/td>\n<\/tr>\n
C1<\/td>\n150 PF SMT<\/td>\n581-12065A151FAT2A<\/td>\n0.72<\/td>\n<\/tr>\n
C2<\/td>\n12 PF SMT<\/td>\n581-12061A120JAT2A<\/td>\n0.26<\/td>\n<\/tr>\n
C3<\/td>\n180 PF SMT<\/td>\n810-CGA5C4C0G2J181J<\/td>\n0.27<\/td>\n<\/tr>\n
C4<\/td>\n68 PF SMT<\/td>\n77-VJ1206A680FXACBC<\/td>\n0.59<\/td>\n<\/tr>\n
C5<\/td>\n50 PF SMT<\/td>\n581-12062A500KAT2A<\/td>\n0.41<\/td>\n<\/tr>\n
C6<\/td>\n10 PF SMT<\/td>\n80-C1206C100J2G<\/td>\n0.54<\/td>\n<\/tr>\n
C7<\/td>\n3 PF SMT<\/td>\n581-12061A3R0CAT2A<\/td>\n0.34<\/td>\n<\/tr>\n
C8<\/td>\n160 PF SMT<\/td>\n581-12065A161J<\/td>\n0.34<\/td>\n<\/tr>\n
Case<\/td>\nDiecast, 4.3 x 2.3\u201d<\/td>\n546-1590WB<\/td>\n10.71<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

I chose a smallish, diecast aluminum case, which matches my other receiver gear.\u00a0 The circuit board noted above is 2.9 x 1.7 inches, which is a little bit small.\u00a0 I used 18 gauge wire between the input\/output connectors and the board.<\/p>\n

The inductors were made by hand.\u00a0 I used a small screwdriver as a winding form, making the turns tightly and then spreading them out to the proper distance.<\/p>\n

Inductor chart:<\/p>\n\n\n\n\n\n\n\n\n
Inductor<\/td>\nValue (nH)<\/td>\nDiameter (mm)<\/td>\nTurns<\/td>\nLength (mm)<\/td>\n<\/tr>\n
L1<\/td>\n173<\/td>\n8<\/td>\n6<\/td>\n9.5<\/td>\n<\/tr>\n
L2<\/td>\n468<\/td>\n8<\/td>\n10<\/td>\n9.8<\/td>\n<\/tr>\n
L3<\/td>\n414<\/td>\n8<\/td>\n9<\/td>\n8.7<\/td>\n<\/tr>\n
L4<\/td>\n146<\/td>\n8<\/td>\n5<\/td>\n7.2<\/td>\n<\/tr>\n
L5<\/td>\n186<\/td>\n8<\/td>\n6<\/td>\n8.6<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

The most expensive part was the circuit board, which cost about $16.00.\u00a0 The rest parts were about $22.00 including shipping.<\/p>\n

As built photos:<\/p>\n

\"HF<\/a>
HF VHF diplexer with components installed<\/figcaption><\/figure>\n
\"HF<\/a>
HF VHF diplexer input side<\/figcaption><\/figure>\n
\"HF<\/a>
HF VHF diplexer completed.<\/figcaption><\/figure>\n

I have installed this already and it works great. I will need to get the spectrum analyzer out and run some signals through the various ports to see the attenuation and 3 dB roll-off points.<\/p>\n","protected":false},"excerpt":{"rendered":"

UPDATE and bump:\u00a0 This post is from eleven years ago, but I have been working on an SDR project using one of the RTL- 2832 chips.\u00a0 I had to make two more of these units, so the prices and part numbers have been updated. I have acquired one of those broad-banded software-defined radios, an Icom … Continue reading HF VHF receiver diplexer<\/span><\/a><\/p>\n","protected":false},"author":4,"featured_media":10977,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4],"tags":[254,157],"class_list":["post-5565","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-tech-stuff","tag-diplexer","tag-swl"],"_links":{"self":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/5565","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/comments?post=5565"}],"version-history":[{"count":17,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/5565\/revisions"}],"predecessor-version":[{"id":10980,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/5565\/revisions\/10980"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/media\/10977"}],"wp:attachment":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/media?parent=5565"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/categories?post=5565"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/tags?post=5565"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}