tag:blogger.com,1999:blog-12559579.post77800611818938819..comments2024-03-28T05:17:55.293-04:00Comments on W2LJ QRP - When you care to send the very least!: Another portable antenna from the QRPGuysQRP - When you care to send the very least!http://www.blogger.com/profile/08707602309223956112noreply@blogger.comBlogger7125tag:blogger.com,1999:blog-12559579.post-22961317139091366952018-04-17T10:14:07.341-04:002018-04-17T10:14:07.341-04:00VE7EZM thanks for infos (I'm not so good in al...VE7EZM thanks for infos (I'm not so good in algebra) 73 Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-12559579.post-16405234325357849622018-04-17T04:03:05.256-04:002018-04-17T04:03:05.256-04:00Anonymous wrote: "Is convinient using an unun...Anonymous wrote: "Is convinient using an unun with 2 radiators attached to it, lets say one for 30m and other for 17 and the rf will find its route with ease"<br /><br />No, it won't. I assume your Unun is designed to feed into a high impedance antenna such as an EFHW. The 17 m antenna will be a bit longer than a quarter wave long on 30 m and would present an impedance Z = R + jX, where R is somewhat higher than 50 ohms and X might be several hundred ohms, on that band. This would be placed in parallel with the several thousand ohm resistive impedance of the 30 ohm EFHW antenna on that band. How well do you think that is going to work on 30 m, when tied to the high impedance end of the Unun?<br /><br />It's just as bad on 17 m. Here the 30 m antenna is going to be a bit shorter than a full wave long on 17 m and will present a fairly high resistance in parallel with some inductance, on that band. Putting that in parallel with the high resistive impedance of the 17 m EFHW antenna will reduce the resistance a lot below what the Unun wants to see, plus put that inductive reactance in parallel with it.<br /><br />I'd far rather use traps and avoid all this, or use a tuner with a single wire a half wave long on the lowest frequency band, or use links on insulators to make the thing a half wave long on whatever band I was using.<br /><br />Paralleling antennas works not too badly with low-impedance center-fed dipoles, though the interaction and resulting necessary trimming is more than I like. Paralleling high impedance antennas is as you can see a different story.<br /><br />Knowing just a little bit about how Z = R + jX and Y = G + jB work (this takes 11th or 12th grade algebra) helps one avoid such mistakes.<br /><br />David VE7EZM and AF7BZDavid Ryeburn VE7EZM and AF7BZhttps://www.blogger.com/profile/10215002968835286422noreply@blogger.comtag:blogger.com,1999:blog-12559579.post-69101618760945352452018-04-13T14:12:01.272-04:002018-04-13T14:12:01.272-04:00Is convinient using an unun with 2 radiators attac...Is convinient using an unun with 2 radiators attached to it, lets say one for 30m and other for 17 and the rf will find its route with easeAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-12559579.post-40466994108866747702018-04-13T08:53:01.354-04:002018-04-13T08:53:01.354-04:00Yes, traps and tuners do incur a small loss; but i...Yes, traps and tuners do incur a small loss; but if you're operating portable and want to communicate on more than one band; do you want to spend your operating time on the air - or putting up resonant antennas for each band?QRP - When you care to send the very least!https://www.blogger.com/profile/08707602309223956112noreply@blogger.comtag:blogger.com,1999:blog-12559579.post-47597020688205443742018-04-13T08:51:16.324-04:002018-04-13T08:51:16.324-04:00The traps are there for people who have rigs that ...The traps are there for people who have rigs that do not have built in tuners; or do not want to carry an external tuner.QRP - When you care to send the very least!https://www.blogger.com/profile/08707602309223956112noreply@blogger.comtag:blogger.com,1999:blog-12559579.post-57496363042114597732018-04-13T04:37:51.317-04:002018-04-13T04:37:51.317-04:00If you want the maximum in qrp pse forget traps an...If you want the maximum in qrp pse forget traps and tuners 73Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-12559579.post-58645689941376585262018-04-12T21:20:32.363-04:002018-04-12T21:20:32.363-04:00If you have a tuner, what do you need the traps fo...If you have a tuner, what do you need the traps for??DaveLhttps://www.blogger.com/profile/01837748113498012191noreply@blogger.com