Radio Preppers

General Category => New To Radio => Topic started by: SlowBro on August 12, 2017, 01:27:38 PM

Title: Do I need an SWR meter for a backpack rig?
Post by: SlowBro on August 12, 2017, 01:27:38 PM
Just bought a 40M QRP Pixie 2 kit off Fleabay. (Yeah yeah I know, not the best, but it'll do for now.) It transmits at under a watt. I'm aiming to keep it and either a Windom or maybe an end fed half wave in my BoB or bike trailer.

Since I may be placing these antennas in different configurations and heights depending where I can find a place to set up, I can imagine the tuner would need to be tweaked often for the best signal. Is an SWR meter strictly required in this situation or can tuning be guesstimated based on prior experience? I would think it'd be required if I used higher power, but I can't see that low wattage doing any damage to the rig if the antenna is not in an optimal location. I would just guess the tuner based on what worked in the past, for that particular antenna height.
Title: Re: Do I need an SWR meter for a backpack rig?
Post by: SlowBro on August 12, 2017, 08:15:54 PM
Say for example I'm at home and string my antenna up a half wavelength in the trees and find that I need to put the tuner dial 3/4 of the way. (I'm building a simple MEF-1 tuner. Schematic (https://drive.google.com/file/d/0B1pQlp8j8NqVdldmbnhNQTNOR28/view).) If I then go out into the woods and put the antenna at about the same height, can I reasonably expect that placing the tuner dial in about the same spot will give about the same SWR? (Knowing that perfection is not required.)
Title: Re: Do I need an SWR meter for a backpack rig?
Post by: SlowBro on August 13, 2017, 05:54:14 AM
Probably a moot question. I just found a circuit (http://qrpkits.com/files/EZ_SWR20170527.pdf) that's super easy to build using stuff I already have on hand and that would vanish into the pack, it's so small and light. I still would like to know the answer, but more for academic reasons.
Title: Re: Do I need an SWR meter for a backpack rig?
Post by: Jon_Garfio on August 13, 2017, 07:58:08 AM
For this qrp activities with a rig without swr meter, I use a endfed antena tunner that tunned throught a variable capacitor or coil, no need swl meter because the perfect tunned is when the maximum noise recepcion.

You can get it the mountain tunner of Sotabeams or the Ilertenna from a spanish dealer.

The ilertenna has a led to sintonize it (minimun bright is the perfect swr tunned).


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Title: Re: Do I need an SWR meter for a backpack rig?
Post by: Jon_Garfio on August 13, 2017, 07:58:48 AM
(https://uploads.tapatalk-cdn.com/20170813/7dac2c5981b674ea9e434a2613f7c79e.jpg)


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Title: Re: Do I need an SWR meter for a backpack rig?
Post by: SlowBro on August 13, 2017, 09:29:28 AM
Yes that looks like the circuit I mentioned in the third post. The LED is actually the SWR "meter" and its brightness changes strength as the reflected power changes. Quite a simple and clever circuit, and should be simple to build and cost little and weigh next to nothing and take up little room in my pack. A win-win.
Title: Re: Do I need an SWR meter for a backpack rig?
Post by: vwflyer on August 13, 2017, 12:52:17 PM
I own both the Sotabeams Mountan tuner and the SOTA Tuner. The second one has the LED indicator. When I hook these to my YouKits radio which has it's own SWR meter I find that the LED does a great job of giving me low SWR on the YouKits meter. However, with the Sotabeams Mountain tuner I found that simply tuning for maximum noise is not accurate enough to assure me low SWR on the YouKits rig. I have to use the rig's SWR meter to bring it down. So I wouldn't recommend a tuner without some kind of SWR indication if your rig doesn't have a meter.
Title: Re: Do I need an SWR meter for a backpack rig?
Post by: SlowBro on August 13, 2017, 06:53:27 PM
Ok but what about in the situation I describe? At home, I tune it. In the field, I put the antenna at about the same height. Would it be sufficient to say the tuner should be placed in roughly the same spot for both locations, or can they really vary that much?
Title: Re: Do I need an SWR meter for a backpack rig?
Post by: vwflyer on August 13, 2017, 10:57:33 PM
From one location to the next I don't have to move the tuning knob very far at all if I don't change my operating frequency. However, those tuners can have a pretty sharp Q. Often times the difference between low SWR and high is just a bump of the knob. If most everything about the two installations are the same (hight of antenna, kind of support, nearby objects, type of ground under it, etc.) it should be really close. But there are so many variables that can affect SWR and you will never be able to exactly duplicate your home setup. The hight of the tuner itself above the ground seems to make a lot of difference. Sometimes I'll stake the tuner down to the ground and sometimes I'll bungie it to a table or a branch. It just depends on my operating position's accommodations. When you set up in a randomly different location every time, you find different arrangements that seem to work best. Without a meter you won't know if it's close enough or not.
Title: Re: Do I need an SWR meter for a backpack rig?
Post by: SlowBro on August 17, 2017, 12:16:46 PM
Thanks all! I'll try to remember to report my success or failure later.
Title: Re: Do I need an SWR meter for a backpack rig?
Post by: cockpitbob on August 22, 2017, 11:07:50 AM
Just a comment on the LED SWR indicator (a.k.a. Tayloe or N7VE indicator).  One of the best parts of it is while you are in Tune mode you cannot hurt your rig.  The worst SWR your rig will see is 2:1.  If the antenna is shorted the Tayloe indicator presents your rig with a 25 Ohm load, and if the antenna is disconnected your rig sees a 100 Ohm load.   I'm a design engineer and to me some of the most brilliant designs are also the simplest.  The Tayloe SWR indicator is truly brilliant.
Title: Re: Do I need an SWR meter for a backpack rig?
Post by: swxx on August 23, 2017, 11:52:21 AM
Ok but what about in the situation I describe? At home, I tune it. In the field, I put the antenna at about the same height. Would it be sufficient to say the tuner should be placed in roughly the same spot for both locations, or can they really vary that much?
Depending on the antenna resonance, e.g. if it is a half wave dipole, and thus quite broad band, then YES in general. And it won't do damage to the Pixie even if you transmit without an antenna (I THINK!). I've used a Pixie for 3000km QSOs but the problem was not just that my signal was very weak, I think it only put out some 350mW or so, on 7023kHz, but also that the receiver seemed very deaf! I suppose with so few components you cannot expect a sensitive receiver! Wide as a barn door doesn't bother me, I have filters in my brain-ears, but lack of sensitivity does. Other stations that were S9 were just copyable. If they had ALSO been using Pixies, no way would the 2-way long distance CW communication have worked. A pixie is a pretty poor choice. But that's just $5 including postage!

Here are good, I hear, QRP 1 Watters and there is a 5 W amplifier there too: they are single band TX/RX but tune a few kHz, I'm thinking to try one: http://www.kitsandparts.com/1watter-V3.php -- at $47 each doesn't it seem a good investment to buy one for each band? If one goes missing, gets squashed, hit by a fly or gets stolen instead of your jewelry, then you are at least not QRT!
Title: Re: Do I need an SWR meter for a backpack rig?
Post by: SlowBro on August 24, 2017, 08:22:14 AM
Just a comment on the LED SWR indicator (a.k.a. Tayloe or N7VE indicator).  One of the best parts of it is while you are in Tune mode you cannot hurt your rig.  The worst SWR your rig will see is 2:1.  If the antenna is shorted the Tayloe indicator presents your rig with a 25 Ohm load, and if the antenna is disconnected your rig sees a 100 Ohm load.   I'm a design engineer and to me some of the most brilliant designs are also the simplest.  The Tayloe SWR indicator is truly brilliant.

Yes indeed the design is brilliant. Based on your comments I searched around and found an SWR indicator (http://wd8rif.com/text/swr_ind.txt) that has specifically been tested on the low-power Pixie I'm building. Going to try that one instead of the one linked earlier. It requires two geranium diodes which I picked up on eBay, USD $3 for 5, US ship.
Title: Re: Do I need an SWR meter for a backpack rig?
Post by: SlowBro on August 24, 2017, 08:29:15 AM
Ok but what about in the situation I describe? At home, I tune it. In the field, I put the antenna at about the same height. Would it be sufficient to say the tuner should be placed in roughly the same spot for both locations, or can they really vary that much?
Depending on the antenna resonance, e.g. if it is a half wave dipole, and thus quite broad band, then YES in general. And it won't do damage to the Pixie even if you transmit without an antenna (I THINK!). I've used a Pixie for 3000km QSOs but the problem was not just that my signal was very weak, I think it only put out some 350mW or so, on 7023kHz, but also that the receiver seemed very deaf! I suppose with so few components you cannot expect a sensitive receiver! Wide as a barn door doesn't bother me, I have filters in my brain-ears, but lack of sensitivity does. Other stations that were S9 were just copyable. If they had ALSO been using Pixies, no way would the 2-way long distance CW communication have worked. A pixie is a pretty poor choice. But that's just $5 including postage!

Here are good, I hear, QRP 1 Watters and there is a 5 W amplifier there too: they are single band TX/RX but tune a few kHz, I'm thinking to try one: http://www.kitsandparts.com/1watter-V3.php -- at $47 each doesn't it seem a good investment to buy one for each band? If one goes missing, gets squashed, hit by a fly or gets stolen instead of your jewelry, then you are at least not QRT!

Maybe I will upgrade soon but I like the path I'm going because the Pixie circuit is simple enough to (mostly) understand and tweak and build on as time goes on. Well aware of the poor selectivity which I aim to somewhat mitigate with this low-pass add-on (http://sp2swi.nawigator.biz/images/pixie-transceiver-schematic-mod.jpg) and also an LM567-based CW filter (http://www.kk5jy.net/cw-modem-v1/). The latter can "lock on" to one tone and filter the rest. I had most of the components I needed already for that, and the chip itself was 3 for a dollar USD, couldn't resist :-)
Title: Re: Do I need an SWR meter for a backpack rig?
Post by: swxx on August 24, 2017, 10:11:02 AM
Good on your for trying and hopefully succeeding! I know one technically very gifted radio amateur who tried and failed... and if you search Youtube for VK3YE making the Pixie slightly less appalling he has some videos on this too which you may already have seen.
Title: Re: Do I need an SWR meter for a backpack rig?
Post by: SlowBro on August 24, 2017, 11:28:35 AM
Well I accepted from the beginning that marginal transmit and wide selectivity would be sufficient since I didn't want to go over budget. Gotta start somewhere. And yep, I saw that video, took notes.

Main concern is getting situational awareness during grid down or EMP. Info on nuke plants especially. If more than a few of those are going up in smoke we should beat feet out of the northern hemisphere. I'm betting that CW will last the longest and go furthest during grid down, and I shouldn't need to transmit very much if anything, I'm sure there will be enough people talking that I can just listen. So I string up an end fed, tune the varicap to find someone talking, plug in and tweak the center frequency on the CW filter. With the end fed I can use a variety of configurations and go DX to NVIS.
Title: Re: Do I need an SWR meter for a backpack rig?
Post by: swxx on August 24, 2017, 09:32:19 PM
Great to meet you SlowBro and good points. For me budget is the big stumbling block to things, even though this is a high priority. For that reason to I started with a Pixie, my first kit, aside from a small CW keyer kit. The pixie though I found very deaf even though I managed contacts thousands of miles but if they had also been on Pixies I'd not have heard them. Good point on listening, though I suspect it would be the same for many, so maybe we don't get much information as everyone is listening and preserving power! For that, nets will be important, I guess.

Once I can manage the cost, I'm thinking PFR-3B is good, except it doesn't have wide receive (so no SSB) and doesn't receive outside the ham bands. It also won't transmit outside the ham bands, which I think is a minus point too, it should be able to go over the edges a bit, in an emergency one is allowed to transmit anywhere. So I'm thinking there is a need for a second portable for receive only, more general coverage, not sure what is available. The other expensive ones such as mountain toppers but to me things that have lots of functions depending on computer chips, I just mistrust as being long term reliable. Components that are large, easy to fix or replace and tolerant, I'd trust more. What if there is a real EOTWAWKI then I don't think finding and replacing components is an option! I would not know how to get soldering iron to work without electricity. Note to self: keep eye out for portable soldering iron.

Good point on the northern hemisphere. Just a quake in Calif long over due will send the entire northern hemisphere into the dark ages. Fuk-U-Shima was nothing learned from except cover ups. Foreign (US) companies supplied all that stuff and they built it on fault lines. What about Calif. In theory, the Southern Hemisphere has no nukes but in reality they may be stationed in Australia or at least on submarines. If that happens the whole world is in a mess. But I think the north would be worst, already is pollution wise. If one has to move far, weight and durability is an issue, and back ups -- more than one TX, more than one RX, spare components. Realistic sources of power. Solar panel, if there is sun getting through after such an event. Me thinks if something like that happens, whoever has batteries or knows how to make them is going to be the new billionaire, locally. Everyone will want batteries. Not sure what for, as aside from radio, not sure what is needed on batteries, lights I guess. People can learn to brush their teeth with sticks surely.
Title: Re: Do I need an SWR meter for a backpack rig?
Post by: SlowBro on August 26, 2017, 03:05:50 PM
Note to self: keep eye out for portable soldering iron.

Got five bucks?
http://www.ebay.com/itm/Gas-Blow-Torch-Soldering-Iron-Gun-Refillable-Butane-Pen-Tool-LW-/232382296450?hash=item361b107182:g:mNgAAOSwhQhY3MJy

Got a piece of wire, tape, and a Bic lighter?
https://www.youtube.com/watch?v=WRpYx8UTveA


Good point on the northern hemisphere. Just a quake in Calif long over due will send the entire northern hemisphere into the dark ages. Fuk-U-Shima was nothing learned from except cover ups. Foreign (US) companies supplied all that stuff and they built it on fault lines. What about Calif. In theory, the Southern Hemisphere has no nukes but in reality they may be stationed in Australia or at least on submarines. If that happens the whole world is in a mess. But I think the north would be worst, already is pollution wise. If one has to move far, weight and durability is an issue, and back ups -- more than one TX, more than one RX, spare components. Realistic sources of power. Solar panel, if there is sun getting through after such an event. Me thinks if something like that happens, whoever has batteries or knows how to make them is going to be the new billionaire, locally. Everyone will want batteries. Not sure what for, as aside from radio, not sure what is needed on batteries, lights I guess. People can learn to brush their teeth with sticks surely.

If I have to beat feet out of the northern hemisphere it would be after listening to the radio reports and committing to the direction of travel no matter what. Thus carrying a radio after taking off wouldn't be as critical; if I had to ditch the radio for some reason, I would.

I happen to have a number of 3V 0.42W solar panels from another project that I'm going to integrate into my pack radio. I'm going to solder them up and tape them together with cardboard and duct tape. Ugly but free 8)
Title: Re: Do I need an SWR meter for a backpack rig?
Post by: swxx on August 27, 2017, 08:40:39 AM
Thanks, very educational, good solutions!