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oldtech

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oldtech last won the day on August 19 2018

oldtech had the most liked content!

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  • Unit Number
    0
  • Location
    Southwest Florida
  • Interests
    GMRS of course. Electronics, physics, chemistry...

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  1. I can commiserate with you Jack. I have twiddled with antennas off and on through the years. But when you need an antenna, and you need it now, it's way too easy to pick one up at a hamfest or off ebay!
  2. I have been building a portable repeater based on the Retevis RT-97. I was using a 5/8 until I received my Comet CA-712EFC. While it didn't extend my range appreciably, it did provide a very nice S/N improvement and helped fill in some 'holes' in coverage. My son lives 5 miles away in an apartment building with a lot of metal siding. He was able to find some spots in the apartment where his 4 watt handheld could hit the repeater reliably, but at best the signal was barely tolerable, lots of annoying fade. With the Comet, he can talk from most spots in his apartment and sounds 'good', not great, but certainly a whole lot better with little fading (he still tends to forget to hold the antenna vertical). While not in the professional, commercial, industrial duty antenna category, I would certainly rate it in the 'Prosumer' category. Easy to assemble and mount, with shrouded N connector, only a little more weight, and about the same wind load as my 5/8. My old antenna exhibited a 1.4:1 SWR attached to the RT-97. While the Comet is advertised as being 1.5 or less, when I tested it I could not see the return loss needle on my meter budge... so I rate it as 1.1 or less for my particular antenna (within my eyeball resolution of an analog SWR meter). So all in all I am currently very pleased. We'll see how it ages.
  3. Man I love the site! What kind of range do you get?
  4. Put the second meter in with the Dremel, the attached photo shows the result.
  5. I wound up using a Dremel cutoff blade for the panel meters. Actually, 2 blades cause the first one choked up! I intentionally cut it 'small', then filed and sanded it to size. It took WAY longer than what I expected, but didn't turn out that bad, though I am now looking into purchasing an economical laser cutter! For the PowerPole connectors, I think I may have another idea.
  6. If the repeater is to be used ONLY by members of your family, who are covered by your GMRS license, then the repeater does not have to identify itself, as long as the users follow the normal GMRS RULES. The RULES say a GMRS user must identify using their (your) callsign every 15 minutes, and/or when concluding a conversation. THEREFORE, the repeater is sufficiently identified by your callsign. If you can wait, rumor has it that a new version of the RT97 will accommodate a third party controller.
  7. Not strictly GMRS related, but I'm hoping for a good answer. I have an enclosure of High Density Polyethylene, in which I want to mount two panel meters and two PowerPole chassis mounts, all rectangular in shape, designed to snap in. I've been musing about what would be the best method of cutting the plastic, and decided to see if anyone had experience with such tasks.
  8. That's great they are working on at least providing a 'hook' for ID and/or external controller. I believe it will greatly increase the appeal. I do not need it for my own use, it's family only. That's basically how I have it mounted now!
  9. TODAY I put the retuned RT97 back on the 22 foot mast, and repeated my drive from memorial day weekend. There really was little difference. It did seem that there was less hiss, but that is entirely subjective. So, my take on it is... my unit arrived properly tuned for 46X.550 as requested. Granted that I made only very slight tweaks, but no doubt that their alignment equipment is much better than mine. Overall it has met my expectations. Though I do have some quibbles. If it had at least a minimal morse code ID at selectable 10 or 15 minute intervals, it's appeal to radio amateurs and GMRS users would vastly expand. I really can't believe their marketing people missed such a simple to add feature. There IS room in the case for an Arduino nano, or similar sized board. So (after hurricane season) I plan to open it up and check out the signal paths, with the goal of making a minimal ID board. Another quibble, as I mentioned before, is the apparent vulnerability of the LCD display board. Other than that, the RT97 is built like a tank. My final quibble is the lack of a convenient way to mount the thing. I'm still trying to figure out an easy way.
  10. I have used my el-cheapo analyzer to retune a few mobile duplexers in the past with good results, though none as small as this one. It is about 1/3 the size of other duplexers I have tuned. The trick is to be careful, take it slow and easy, and use plastic tweaking tools (I inherited a nice set from my grandfather). I did retest the RT97 after this tuning, in the shack. Still 5 watts out, and still near 1.1 swr ( I have an old analog swr meter, so judge accordingly). When the storms clear up here (probably tomorrow morning), I will be putting it back on the mast for further testing... I know that what looks good in the lab doesn't always work well out in the real world :).
  11. The seller I originally bought it from no longer has it, but here is a page of identical items... https://www.ebay.com/sch/i.html?_id=113144841014&_nkw=U%2FV+UHF+VHF+dual+band+spectrum+analyzer+with+tracking+source+tuning+Duplexers+WL
  12. I have a cheap spectrum analyzer, but I have been hoping someone would test the RT97 duplexer with a quality analyzer and post the results. Since that hasn't happened yet, I decided to bite the bullet, and do it myself. Hopefully someone with a quality instrument will see this and add to it. A bit of background first. I ordered my repeater configured for 46X.550. I received it a month ago, but haven't had time to play with it until the Memorial day weekend. That weekend I did a field test, with a dipole on a 20 foot portable tripod mast. I was pleased to see a solid 5 watts out, with swr very close to 1.1. I then set my mobile to 5 watts and started to drive. I expected to get about 8 to 9 miles range, here in the flatlands of Southwest Florida, and I was pleased with the results. In one direction I went to an area which lies a few feet lower than the repeater location, and went nearly 12 miles before the S meter dipped below 2 and began to flutter. I took out the duplexer and attached it to the cheap analyzer I got for $100 via Ebay. The low side notch, supposed to be at 462.5500 Mhz, was actually at 462.7010, as shown in the first photo. The tracking generator of this analyzer is about -30 dBm, so this shows an attenuation of 87 dB at the notch. Not bad for such a tiny duplexer, but at the desired frequency there was only 71 dB attenuation. After I tweaked it, I got the notch centered on 462.5500 at an attenuation of 80 dB, shown in the next photo. Next up I looked at the high side, where the notch was supposed to be at 467.5500 Mhz. It was actually at 467.4896, with 83 dB attenuation as shown below. A little tweak gave me 80 dB attenuation at the desired frequency. If I get the time this weekend, I'll do another field test with the tweaked duplexer and comment on here with the results.
  13. Sometimes ducting is confused with skip, but they are two different effects. 'Skip' is dependant on the state of the ionosphere, and that greatly depends on the solar sunspot cycle. When the cycle is active, particles emitted by the sun energizes the ionosphere, which reflects certain radio frequencies. Because the ionosphere is so high, those reflected signals can travel hundreds of miles, even thousands sometimes. Because the planet is surrounded by the ionosphere, 'Skip' is a world wide event. Ducting is a weaker, much more localized event, though it has been recorded at least once to have carried a signal over a thousand miles. Ducting occurs during an atmospheric thermal inversion. The density differences caused thereby can refract RF energy that is headed skyward back to the earth. Beginning about 11 PM EDT tonight (4/16/2021), a ducting event will begin to affect Florida. From near 2 AM to around 10 AM the effect should be quite strong. From 6 to 7, I will be listening and calling on the GMRS 'travel' channel, 462.675 with tone 141.3. Just for the fun of it. If you hear my call sign, you know it's all the way from Punta Gorda.
  14. Actually, it is 'possible' under certain conditions of Tropospheric ducting, which has been strongly affecting large parts of Florida recently. I myself overheard a conversation over a repeater near Orlando earlier this week, while I am in Punta Gorda... well over 100 miles. I have also had several contact with an 'Amateur operator' in West Palm who especially enjoys making contacts during ducting event, that's nearly 150 miles away from me.
  15. After Hurricane Irma I started thinking about backup communications for the family. There is a nearby repeater which, at about 200 foot altitude, covers the entire area that we live and work in. I also purchased a used 'mobile' repeater as a backup, to be quickly erected after a storm in case the 'tall' repeater fails. It provides about 5 miles of coverage (on a clear day when the moon is full ). Not a whole lot of range, but it still covers our homes. I am about to upgrade that repeater with the goal of 10 miles range. I decided at the same time I got my GMRS license, to get my Amateur license. As I am nearing retirement, I realized that I will go nuts without a hobby, and it provides an additional source of information and communications during times of emergency.
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