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Remote tuner specs
I was looking at a MFJ remote antenna tuner, and it is specified as being
able to match 12 to 1600 ohms. What does that mean? At 12 ohms the SWR would be about 4.2:1 and at 1600 ohms a SWR of about 32:1. If one started from 1600 ohms around a Smith chart, the circle would intersect at the other side at about 0.64 ohms. Likewise starting at 12 ohms and going halfway around the chart would end up at 210 ohms, not 1600. How does one use the specs if the antenna to be matched has a complex impedance? Look at the internal tuner component ranges? |
Remote tuner specs
Wayne wrote:
I was looking at a MFJ remote antenna tuner, and it is specified as being able to match 12 to 1600 ohms. What does that mean? At 12 ohms the SWR would be about 4.2:1 and at 1600 ohms a SWR of about 32:1. If one started from 1600 ohms around a Smith chart, the circle would intersect at the other side at about 0.64 ohms. Likewise starting at 12 ohms and going halfway around the chart would end up at 210 ohms, not 1600. How does one use the specs if the antenna to be matched has a complex impedance? Look at the internal tuner component ranges? Those ranges of impedances are basically worthless. Looking at the component ranges is probably the best, but most complex way. Some makers give half way usefull info with things like will tune a minumum of X feet long at 160 M. I have both a SGC and a LDG; the SGC is much better range wise. -- Jim Pennino |
Remote tuner specs
On 8/9/2015 12:23 PM, Wayne wrote:
I was looking at a MFJ remote antenna tuner, and it is specified as being able to match 12 to 1600 ohms. What does that mean? At 12 ohms the SWR would be about 4.2:1 and at 1600 ohms a SWR of about 32:1. The 12 to 1600 ohms is the RANGE that the tuner is capable of matching. Forget SWR because it has no meaning at this point. If one started from 1600 ohms around a Smith chart, the circle would intersect at the other side at about 0.64 ohms. You are not analyzing this correctly. If you are really comfortable with a Smith chart, put a capacitor across the 1600 ohms and then put an inductor in series with the results. By adjusting the values, you can achieve a 50 ohm output. Likewise starting at 12 ohms and going halfway around the chart would end up at 210 ohms, not 1600. This is similar to the above, but now you want a series impedance and a shunt impedance following it. How does one use the specs if the antenna to be matched has a complex impedance? Look at the internal tuner component ranges? That is a good question. Do you want to buy the tuner and tear it down to explore the component ranges, or would it be better to ask the designers? You should ask them to define the type (complex impedance) of the load to which their specs apply. |
Remote tuner specs
"John S" wrote in message ... On 8/9/2015 12:23 PM, Wayne wrote: I was looking at a MFJ remote antenna tuner, and it is specified as being able to match 12 to 1600 ohms. What does that mean? At 12 ohms the SWR would be about 4.2:1 and at 1600 ohms a SWR of about 32:1. The 12 to 1600 ohms is the RANGE that the tuner is capable of matching. Forget SWR because it has no meaning at this point. That's a bit of what I was getting at. I have another tuner rated for 4:1 SWR, and I assume that means it will match all the way around the 4 circle. I don't know what to do with a 12 to 1600 ohm spec. If one started from 1600 ohms around a Smith chart, the circle would intersect at the other side at about 0.64 ohms. You are not analyzing this correctly. If you are really comfortable with a Smith chart, put a capacitor across the 1600 ohms and then put an inductor in series with the results. By adjusting the values, you can achieve a 50 ohm output. Likewise starting at 12 ohms and going halfway around the chart would end up at 210 ohms, not 1600. This is similar to the above, but now you want a series impedance and a shunt impedance following it. I was just showing that the 12 and 1600 are not on the same circle. How does one use the specs if the antenna to be matched has a complex impedance? Look at the internal tuner component ranges? That is a good question. Do you want to buy the tuner and tear it down to explore the component ranges, or would it be better to ask the designers? You should ask them to define the type (complex impedance) of the load to which their specs apply. I suspect the designers have a gag order from the marketing guys. |
Remote tuner specs
wrote in message ... Wayne wrote: Those ranges of impedances are basically worthless. I don't agree :-) If I had to test such a tuner the first thing I would do is put a pure resistor of those values and try to match them accross the frequency and power range announced. Measuring the insertion loss would be nice too. Of course it is not the complete story but a good start. |
Remote tuner specs
"bilou" wrote in message ... wrote in message ... Wayne wrote: Those ranges of impedances are basically worthless. I don't agree :-) If I had to test such a tuner the first thing I would do is put a pure resistor of those values and try to match them accross the frequency and power range announced. Measuring the insertion loss would be nice too. Of course it is not the complete story but a good start. That's true, but I would like for the specs to give me an idea if I want to buy it. |
Remote tuner specs
bilou wrote:
wrote in message ... Wayne wrote: Those ranges of impedances are basically worthless. I don't agree :-) If I had to test such a tuner the first thing I would do is put a pure resistor of those values and try to match them accross the frequency and power range announced. Measuring the insertion loss would be nice too. Of course it is not the complete story but a good start. Which basically tells you nothing about the ability to match a complex load. I measured the impdance of a vertical to be well under the specified limits of the LDG tuner I own. However, it fails to get a match on 160 M and 17 M. The SGC tuner has no problems getting a match. -- Jim Pennino |
Remote tuner specs
On 8/9/2015 4:24 PM, Wayne wrote:
"John S" wrote in message ... On 8/9/2015 12:23 PM, Wayne wrote: I was looking at a MFJ remote antenna tuner, and it is specified as being able to match 12 to 1600 ohms. What does that mean? At 12 ohms the SWR would be about 4.2:1 and at 1600 ohms a SWR of about 32:1. I don't know what to do with a 12 to 1600 ohm spec. If one started from 1600 ohms around a Smith chart, the circle would intersect at the other side at about 0.64 ohms. Likewise starting at 12 ohms and going halfway around the chart would end up at 210 ohms, not 1600. I was just showing that the 12 and 1600 are not on the same circle. Now I think I understand your point. I had not considered that you are thinking in terms of the matching capability using SWR circles on the chart. Very interesting and quite useful if the specs can be assumed to mean that. I have a gut feeling that the 1600 is a bit far out and that the 12 is more realistic, but I have never used a tuner. My stuff was always one-band designed so just fixed matching values suited. If I learn anything I get back to you. Sorry I couldn't help. |
Remote tuner specs
On 8/9/2015 12:23 PM, Wayne wrote:
I was looking at a MFJ remote antenna tuner, and it is specified as being able to match 12 to 1600 ohms. What does that mean? At 12 ohms the SWR would be about 4.2:1 and at 1600 ohms a SWR of about 32:1. If one started from 1600 ohms around a Smith chart, the circle would intersect at the other side at about 0.64 ohms. Likewise starting at 12 ohms and going halfway around the chart would end up at 210 ohms, not 1600. How does one use the specs if the antenna to be matched has a complex impedance? Look at the internal tuner component ranges? What antenna are you thinking to match? |
Remote tuner specs
In article ,
"Wayne" wrote: I was looking at a MFJ remote antenna tuner, and it is specified as being able to match 12 to 1600 ohms. What does that mean? At 12 ohms the SWR would be about 4.2:1 and at 1600 ohms a SWR of about 32:1. If one started from 1600 ohms around a Smith chart, the circle would intersect at the other side at about 0.64 ohms. Likewise starting at 12 ohms and going halfway around the chart would end up at 210 ohms, not 1600. How does one use the specs if the antenna to be matched has a complex impedance? Look at the internal tuner component ranges? Wayne- Your Smith Chart is normalized to 50 Ohms, but the tuner may not have a "characteristic impedance". So to use the Smith Chart approach, assume that it does. In that case, Z divided by 12 is equal to 1600 divided by Z. Therefore Z squared is equal to the product of 12 and 1600, or Z = 138.6 Ohms. You can normalize a Smith Chart to that value. Now see if the tuner will work with all values within the circle! Fred K4DII |
Remote tuner specs
"Fred McKenzie" wrote in message ... In article , "Wayne" wrote: I was looking at a MFJ remote antenna tuner, and it is specified as being able to match 12 to 1600 ohms. What does that mean? At 12 ohms the SWR would be about 4.2:1 and at 1600 ohms a SWR of about 32:1. If one started from 1600 ohms around a Smith chart, the circle would intersect at the other side at about 0.64 ohms. Likewise starting at 12 ohms and going halfway around the chart would end up at 210 ohms, not 1600. How does one use the specs if the antenna to be matched has a complex impedance? Look at the internal tuner component ranges? Your Smith Chart is normalized to 50 Ohms, but the tuner may not have a "characteristic impedance". So to use the Smith Chart approach, assume that it does. In that case, Z divided by 12 is equal to 1600 divided by Z. Therefore Z squared is equal to the product of 12 and 1600, or Z = 138.6 Ohms. You can normalize a Smith Chart to that value. Now see if the tuner will work with all values within the circle! I suppose that would help a bit. Thanks. |
Remote tuner specs
"John S" wrote in message ... On 8/9/2015 12:23 PM, Wayne wrote: I was looking at a MFJ remote antenna tuner, and it is specified as being able to match 12 to 1600 ohms. What does that mean? At 12 ohms the SWR would be about 4.2:1 and at 1600 ohms a SWR of about 32:1. If one started from 1600 ohms around a Smith chart, the circle would intersect at the other side at about 0.64 ohms. Likewise starting at 12 ohms and going halfway around the chart would end up at 210 ohms, not 1600. How does one use the specs if the antenna to be matched has a complex impedance? Look at the internal tuner component ranges? # What antenna are you thinking to match? My yard is very difficult for getting antennas up. I currently use a vertical on 20-10 that is mounted on top of a rather large metal patio cover. The cover does have AC voltage available for patio lights/fans/bird bath pump and such. So I could power a remote tuner separate from the coax if required. The current antenna for 20-10 is a 14.5 foot vertical, fed with a short run of good coax and tuned at the rig end of the coax. IIRC, the swr is about 6:1 on 20 meters, dips around 18 MHz and rises to about 20:1 on 10 meters. For 20:1 the charts say I will lose not more than 3 db with the short run of coax, which is acceptable. In practice, the antenna is performing well enough for me to leave it alone. .....but you know how hams are..... |
Remote tuner specs
wrote in message ... bilou wrote: wrote in message ... Wayne wrote: Those ranges of impedances are basically worthless. I don't agree :-) If I had to test such a tuner the first thing I would do is put a pure resistor of those values and try to match them accross the frequency and power range announced. Measuring the insertion loss would be nice too. Of course it is not the complete story but a good start. Which basically tells you nothing about the ability to match a complex load. Hello You are absolutely right in fact a perfect ferrite transformer would be better. But an aerial must have a real impedance part to be of any use :-) Specifications must be easy to verify. Here it is the case. How do you check the 0.1dB noise figure advocated by many LNB's ? :-) |
Remote tuner specs
bilou wrote:
wrote in message ... bilou wrote: wrote in message ... Wayne wrote: Those ranges of impedances are basically worthless. I don't agree :-) If I had to test such a tuner the first thing I would do is put a pure resistor of those values and try to match them accross the frequency and power range announced. Measuring the insertion loss would be nice too. Of course it is not the complete story but a good start. Which basically tells you nothing about the ability to match a complex load. Hello You are absolutely right in fact a perfect ferrite transformer would be better. It is rather difficult for a ferrite transformer to convert a random complex impedance to approximately 50 Ohm resistive, which is what an autotuner does. But an aerial must have a real impedance part to be of any use :-) Which is why one uses an autotuner to convert the random complex impedance to approximately 50 Ohm resistive. Specifications must be easy to verify. And life must be fair... Here it is the case. How do you check the 0.1dB noise figure advocated by many LNB's ? With test equipment. -- Jim Pennino |
Remote tuner specs
On 8/9/2015 4:24 PM, Wayne wrote:
"John S" wrote in message ... On 8/9/2015 12:23 PM, Wayne wrote: I was looking at a MFJ remote antenna tuner, and it is specified as being able to match 12 to 1600 ohms. What does that mean? At 12 ohms the SWR would be about 4.2:1 and at 1600 ohms a SWR of about 32:1. The 12 to 1600 ohms is the RANGE that the tuner is capable of matching. Forget SWR because it has no meaning at this point. That's a bit of what I was getting at. I have another tuner rated for 4:1 SWR, and I assume that means it will match all the way around the 4 circle. I don't know what to do with a 12 to 1600 ohm spec. If one started from 1600 ohms around a Smith chart, the circle would intersect at the other side at about 0.64 ohms. You are not analyzing this correctly. If you are really comfortable with a Smith chart, put a capacitor across the 1600 ohms and then put an inductor in series with the results. By adjusting the values, you can achieve a 50 ohm output. Likewise starting at 12 ohms and going halfway around the chart would end up at 210 ohms, not 1600. This is similar to the above, but now you want a series impedance and a shunt impedance following it. I was just showing that the 12 and 1600 are not on the same circle. How does one use the specs if the antenna to be matched has a complex impedance? Look at the internal tuner component ranges? That is a good question. Do you want to buy the tuner and tear it down to explore the component ranges, or would it be better to ask the designers? You should ask them to define the type (complex impedance) of the load to which their specs apply. I suspect the designers have a gag order from the marketing guys. I found the following on the MFJ site for the MFJ-998RT. See page 2 at this link: http://www.mfjenterprises.com/Downlo...df&company=mfj •Impedance matching range: 12 to 1600 ohms •SWR matching range: up to 4:1 for 50 ohms and upto 32:1 for 50 ohms •Minimum power for tuning: 5 watts •Maximum power while tuning: 100 watts with foldback, 20 watts without foldback •RF power limit: 1500 watts SSB/CW •Frequency range: 1.8 to 30 MHz continuous coverage •Frequency counter accuracy: ±1 kHz across HF bands •Capacitance range: 0 to 3926 pF nominal (256 values) on input side 0 to 976 pF nominal (64 values) on output side •Inductance range: 0 to 24.28 µH nominal (256 values) |
Remote tuner specs
On 8/11/2015 6:18 PM, John S wrote:
On 8/9/2015 4:24 PM, Wayne wrote: "John S" wrote in message ... On 8/9/2015 12:23 PM, Wayne wrote: I was looking at a MFJ remote antenna tuner, and it is specified as being able to match 12 to 1600 ohms. What does that mean? At 12 ohms the SWR would be about 4.2:1 and at 1600 ohms a SWR of about 32:1. The 12 to 1600 ohms is the RANGE that the tuner is capable of matching. Forget SWR because it has no meaning at this point. That's a bit of what I was getting at. I have another tuner rated for 4:1 SWR, and I assume that means it will match all the way around the 4 circle. I don't know what to do with a 12 to 1600 ohm spec. If one started from 1600 ohms around a Smith chart, the circle would intersect at the other side at about 0.64 ohms. You are not analyzing this correctly. If you are really comfortable with a Smith chart, put a capacitor across the 1600 ohms and then put an inductor in series with the results. By adjusting the values, you can achieve a 50 ohm output. Likewise starting at 12 ohms and going halfway around the chart would end up at 210 ohms, not 1600. This is similar to the above, but now you want a series impedance and a shunt impedance following it. I was just showing that the 12 and 1600 are not on the same circle. How does one use the specs if the antenna to be matched has a complex impedance? Look at the internal tuner component ranges? That is a good question. Do you want to buy the tuner and tear it down to explore the component ranges, or would it be better to ask the designers? You should ask them to define the type (complex impedance) of the load to which their specs apply. I suspect the designers have a gag order from the marketing guys. I found the following on the MFJ site for the MFJ-998RT. See page 2 at this link: http://www.mfjenterprises.com/Downlo...df&company=mfj •Impedance matching range: 12 to 1600 ohms •SWR matching range: up to 4:1 for 50 ohms and upto 32:1 for 50 ohms •Minimum power for tuning: 5 watts •Maximum power while tuning: 100 watts with foldback, 20 watts without foldback •RF power limit: 1500 watts SSB/CW •Frequency range: 1.8 to 30 MHz continuous coverage •Frequency counter accuracy: ±1 kHz across HF bands •Capacitance range: 0 to 3926 pF nominal (256 values) on input side 0 to 976 pF nominal (64 values) on output side •Inductance range: 0 to 24.28 µH nominal (256 values) I think their minimums are not realistic. I would not know how to achieve 0pF with a 3926pF variable cap, for example. Also, why 3926 rather than 3900 or even 3920? It isn't all that easy to measure 6pF out of 3920pF. I'm thinking that somebody just threw some numbers at the spec sheet. BUT! It is better than nothing and may help to make some reasonable judgements. |
Remote tuner specs
On 8/10/2015 8:30 PM, Wayne wrote:
"John S" wrote in message ... On 8/9/2015 12:23 PM, Wayne wrote: I was looking at a MFJ remote antenna tuner, and it is specified as being able to match 12 to 1600 ohms. What does that mean? At 12 ohms the SWR would be about 4.2:1 and at 1600 ohms a SWR of about 32:1. If one started from 1600 ohms around a Smith chart, the circle would intersect at the other side at about 0.64 ohms. Likewise starting at 12 ohms and going halfway around the chart would end up at 210 ohms, not 1600. How does one use the specs if the antenna to be matched has a complex impedance? Look at the internal tuner component ranges? # What antenna are you thinking to match? My yard is very difficult for getting antennas up. I currently use a vertical on 20-10 that is mounted on top of a rather large metal patio cover. The cover does have AC voltage available for patio lights/fans/bird bath pump and such. So I could power a remote tuner separate from the coax if required. The current antenna for 20-10 is a 14.5 foot vertical, fed with a short run of good coax and tuned at the rig end of the coax. IIRC, the swr is about 6:1 on 20 meters, dips around 18 MHz and rises to about 20:1 on 10 meters. For 20:1 the charts say I will lose not more than 3 db with the short run of coax, which is acceptable. In practice, the antenna is performing well enough for me to leave it alone. ....but you know how hams are..... I remember now. I even made an EZNEC model (including your metal patio) and got results for all the ham bands. Using the specs for the MFJ-998RT, it seems that it may match all but the 1.8MHz band IF the specs can be relied upon. I don't want to encourage you to spend a lot of money based on my input. I just had fun doing the modelling. |
Remote tuner specs
In article , John S wrote:
I think their minimums are not realistic. I would not know how to achieve 0pF with a 3926pF variable cap, for example. Also, why 3926 rather than 3900 or even 3920? It isn't all that easy to measure 6pF out of 3920pF. I'm thinking that somebody just threw some numbers at the spec sheet. BUT! It is better than nothing and may help to make some reasonable judgements. Typically, these tuners use banks of capacitors, switched in and out (parallel for caps, series for inductors) using relays. The components are often in a 1:2:4:8:... power series. "256 values" implies 8 components, and 8 relays, giving you anywhere from 0 to 255 times the "fundamental" value. I expect that "0" means "all caps open, or all inductors shorted", and "3926" is the sum of the nominal values of the caps in the bank. If their starting value is around 15 pF, 255 times that would be 3825; add in a few pF of stray capacitance per relay and you'd be in the neighborhood of 3926. (Having figures like that, in the face of component variations and strays and measurement errors, reminds me a bit of some dialog from Harry Harrison's "Star Smashers of the Galaxy Rangers." "[certain ancient events] took place approximately 14 billion years ago." "That figure is exact?" "Of course." ) |
Remote tuner specs
John S wrote:
On 8/11/2015 6:18 PM, John S wrote: On 8/9/2015 4:24 PM, Wayne wrote: "John S" wrote in message ... On 8/9/2015 12:23 PM, Wayne wrote: I was looking at a MFJ remote antenna tuner, and it is specified as being able to match 12 to 1600 ohms. What does that mean? At 12 ohms the SWR would be about 4.2:1 and at 1600 ohms a SWR of about 32:1. The 12 to 1600 ohms is the RANGE that the tuner is capable of matching. Forget SWR because it has no meaning at this point. That's a bit of what I was getting at. I have another tuner rated for 4:1 SWR, and I assume that means it will match all the way around the 4 circle. I don't know what to do with a 12 to 1600 ohm spec. If one started from 1600 ohms around a Smith chart, the circle would intersect at the other side at about 0.64 ohms. You are not analyzing this correctly. If you are really comfortable with a Smith chart, put a capacitor across the 1600 ohms and then put an inductor in series with the results. By adjusting the values, you can achieve a 50 ohm output. Likewise starting at 12 ohms and going halfway around the chart would end up at 210 ohms, not 1600. This is similar to the above, but now you want a series impedance and a shunt impedance following it. I was just showing that the 12 and 1600 are not on the same circle. How does one use the specs if the antenna to be matched has a complex impedance? Look at the internal tuner component ranges? That is a good question. Do you want to buy the tuner and tear it down to explore the component ranges, or would it be better to ask the designers? You should ask them to define the type (complex impedance) of the load to which their specs apply. I suspect the designers have a gag order from the marketing guys. I found the following on the MFJ site for the MFJ-998RT. See page 2 at this link: http://www.mfjenterprises.com/Downlo...df&company=mfj ?Impedance matching range: 12 to 1600 ohms ?SWR matching range: up to 4:1 for 50 ohms and upto 32:1 for 50 ohms ?Minimum power for tuning: 5 watts ?Maximum power while tuning: 100 watts with foldback, 20 watts without foldback ?RF power limit: 1500 watts SSB/CW ?Frequency range: 1.8 to 30 MHz continuous coverage ?Frequency counter accuracy: ?1 kHz across HF bands ?Capacitance range: 0 to 3926 pF nominal (256 values) on input side 0 to 976 pF nominal (64 values) on output side ?Inductance range: 0 to 24.28 ?H nominal (256 values) I think their minimums are not realistic. I would not know how to achieve 0pF with a 3926pF variable cap, for example. Also, why 3926 rather than 3900 or even 3920? It isn't all that easy to measure 6pF out of 3920pF. I'm thinking that somebody just threw some numbers at the spec sheet. BUT! It is better than nothing and may help to make some reasonable judgements. The parts in a modern autotuner are not variable, they are a bunch of fixed components switched in and out by relays. The 3926 pF is the value of ALL the capacitors in parallel and 0 pF would be a straight connection. -- Jim Pennino |
Remote tuner specs
On 8/11/2015 7:17 PM, Dave Platt wrote:
In article , John S wrote: I think their minimums are not realistic. I would not know how to achieve 0pF with a 3926pF variable cap, for example. Also, why 3926 rather than 3900 or even 3920? It isn't all that easy to measure 6pF out of 3920pF. I'm thinking that somebody just threw some numbers at the spec sheet. BUT! It is better than nothing and may help to make some reasonable judgements. Typically, these tuners use banks of capacitors, switched in and out (parallel for caps, series for inductors) using relays. The components are often in a 1:2:4:8:... power series. "256 values" implies 8 components, and 8 relays, giving you anywhere from 0 to 255 times the "fundamental" value. I expect that "0" means "all caps open, or all inductors shorted", and "3926" is the sum of the nominal values of the caps in the bank. If their starting value is around 15 pF, 255 times that would be 3825; add in a few pF of stray capacitance per relay and you'd be in the neighborhood of 3926. (Having figures like that, in the face of component variations and strays and measurement errors, reminds me a bit of some dialog from Harry Harrison's "Star Smashers of the Galaxy Rangers." "[certain ancient events] took place approximately 14 billion years ago." "That figure is exact?" "Of course." Haw! Very good, Dave. It seems that I am a fossil. The world changed while I slept. Thanks for the education. |
Sig figs (Was: Remote tuner specs)
In article ,
(Dave Platt) wrote: "[certain ancient events] took place approximately 14 billion years ago." "That figure is exact?" This reminds me of something I heard about 40 years ago from an electrical engineer while on a hiking trip in Garibaldi Provincial Park in British Columbia. The EE reported on a conversation he had had some years earlier with the person then in charge of a remote cabin, near which we had just then stopped for a rest break. EE: How old are those mountains (pointing over towards Mamquam Mountain)? Cabin steward: 10 million and 30 years old. EE: And how did you find that out? Cabin steward: 30 years ago a geologist stayed in the cabin and I asked him. He said they were 10 million years old. I used to tell this story to my students when I wanted to get across the idea of significant figures. -- David Ryeburn To send e-mail, change "netz" to "net" |
Remote tuner specs
"John S" wrote in message ... On 8/10/2015 8:30 PM, Wayne wrote: "John S" wrote in message ... On 8/9/2015 12:23 PM, Wayne wrote: I was looking at a MFJ remote antenna tuner, and it is specified as being able to match 12 to 1600 ohms. What does that mean? At 12 ohms the SWR would be about 4.2:1 and at 1600 ohms a SWR of about 32:1. If one started from 1600 ohms around a Smith chart, the circle would intersect at the other side at about 0.64 ohms. Likewise starting at 12 ohms and going halfway around the chart would end up at 210 ohms, not 1600. How does one use the specs if the antenna to be matched has a complex impedance? Look at the internal tuner component ranges? # What antenna are you thinking to match? My yard is very difficult for getting antennas up. I currently use a vertical on 20-10 that is mounted on top of a rather large metal patio cover. The cover does have AC voltage available for patio lights/fans/bird bath pump and such. So I could power a remote tuner separate from the coax if required. The current antenna for 20-10 is a 14.5 foot vertical, fed with a short run of good coax and tuned at the rig end of the coax. IIRC, the swr is about 6:1 on 20 meters, dips around 18 MHz and rises to about 20:1 on 10 meters. For 20:1 the charts say I will lose not more than 3 db with the short run of coax, which is acceptable. In practice, the antenna is performing well enough for me to leave it alone. ....but you know how hams are..... # I remember now. I even made an EZNEC model (including your metal patio) # and got results for all the ham bands. Using the specs for the # MFJ-998RT, it seems that it may match all but the 1.8MHz band IF the # specs can be relied upon. # I don't want to encourage you to spend a lot of money based on my input. # I just had fun doing the modelling. That's what money is for...to buy toys. Nowadays for me, that means radio gear, cameras or guns :) |
Remote tuner specs
Wayne wrote:
"John S" wrote in message ... On 8/10/2015 8:30 PM, Wayne wrote: "John S" wrote in message ... On 8/9/2015 12:23 PM, Wayne wrote: I was looking at a MFJ remote antenna tuner, and it is specified as being able to match 12 to 1600 ohms. What does that mean? At 12 ohms the SWR would be about 4.2:1 and at 1600 ohms a SWR of about 32:1. If one started from 1600 ohms around a Smith chart, the circle would intersect at the other side at about 0.64 ohms. Likewise starting at 12 ohms and going halfway around the chart would end up at 210 ohms, not 1600. How does one use the specs if the antenna to be matched has a complex impedance? Look at the internal tuner component ranges? # What antenna are you thinking to match? My yard is very difficult for getting antennas up. I currently use a vertical on 20-10 that is mounted on top of a rather large metal patio cover. The cover does have AC voltage available for patio lights/fans/bird bath pump and such. So I could power a remote tuner separate from the coax if required. The current antenna for 20-10 is a 14.5 foot vertical, fed with a short run of good coax and tuned at the rig end of the coax. IIRC, the swr is about 6:1 on 20 meters, dips around 18 MHz and rises to about 20:1 on 10 meters. For 20:1 the charts say I will lose not more than 3 db with the short run of coax, which is acceptable. In practice, the antenna is performing well enough for me to leave it alone. ....but you know how hams are..... # I remember now. I even made an EZNEC model (including your metal patio) # and got results for all the ham bands. Using the specs for the # MFJ-998RT, it seems that it may match all but the 1.8MHz band IF the # specs can be relied upon. # I don't want to encourage you to spend a lot of money based on my input. # I just had fun doing the modelling. That's what money is for...to buy toys. Nowadays for me, that means radio gear, cameras or guns :) Hams substitute the word 'necessities' for 'Toys'! :-) Irv VE6BP |
Remote tuner specs
"Irv Finkleman" wrote in message ... Wayne wrote: "John S" wrote in message ... On 8/10/2015 8:30 PM, Wayne wrote: "John S" wrote in message ... On 8/9/2015 12:23 PM, Wayne wrote: I was looking at a MFJ remote antenna tuner, and it is specified as being able to match 12 to 1600 ohms. What does that mean? At 12 ohms the SWR would be about 4.2:1 and at 1600 ohms a SWR of about 32:1. If one started from 1600 ohms around a Smith chart, the circle would intersect at the other side at about 0.64 ohms. Likewise starting at 12 ohms and going halfway around the chart would end up at 210 ohms, not 1600. How does one use the specs if the antenna to be matched has a complex impedance? Look at the internal tuner component ranges? # What antenna are you thinking to match? My yard is very difficult for getting antennas up. I currently use a vertical on 20-10 that is mounted on top of a rather large metal patio cover. The cover does have AC voltage available for patio lights/fans/bird bath pump and such. So I could power a remote tuner separate from the coax if required. The current antenna for 20-10 is a 14.5 foot vertical, fed with a short run of good coax and tuned at the rig end of the coax. IIRC, the swr is about 6:1 on 20 meters, dips around 18 MHz and rises to about 20:1 on 10 meters. For 20:1 the charts say I will lose not more than 3 db with the short run of coax, which is acceptable. In practice, the antenna is performing well enough for me to leave it alone. ....but you know how hams are..... # I remember now. I even made an EZNEC model (including your metal patio) # and got results for all the ham bands. Using the specs for the # MFJ-998RT, it seems that it may match all but the 1.8MHz band IF the # specs can be relied upon. # I don't want to encourage you to spend a lot of money based on my input. # I just had fun doing the modelling. That's what money is for...to buy toys. Nowadays for me, that means radio gear, cameras or guns :) # Hams substitute the word 'necessities' for 'Toys'! :-) LOL...yep, of the three categories of necessities, I'm lagging a bit with radios :) |
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