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end fed 1/2 wave UHF antenna for SABER with MX mount

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RFI-EMI-GUY

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I would like to make an end fed 1/2 wave UHF antenna for a SABER radio having MX thread mount I am trying to determine how best to match the antenna to the radio, The MX mount does not provide a ground return nor does the radio provide a reliable point to furnish a ground return. The radio chassis of course would be the counterpoise, in any event. The issue is feed point impedance at the stud mount.

I see a lot of discussion about end fed HF antennas, and these always seem to involve a matching transformer or other solution requiring a ground return lead.

I prefer the 1/2 wave as the pattern is cleaner than a 5/8 wave solution.

Has anyone a solution for this?

Oh yes, I have searched for one ready made, but not finding it. Would buy if I can.

(Moved thread to here)
 
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RFI-EMI-GUY

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I would like to make an end fed 1/2 wave UHF antenna for a SABER radio having MX thread mount I am trying to determine how best to match the antenna to the radio, The MX mount does not provide a ground return nor does the radio provide a reliable point to furnish a ground return. The radio chassis of course would be the counterpoise, in any event. The issue is feed point impedance at the stud mount.

I see a lot of discussion about end fed HF antennas, and these always seem to involve a matching transformer or other solution requiring a ground return lead.

I prefer the 1/2 wave as the pattern is cleaner than a 5/8 wave solution.

Has anyone a solution for this?

Oh yes, I have searched for one ready made, but not finding it. Would buy if I can.

(Moved thread to here)
Hmm, I might go 5/8 wave if I must?

Any thoughts either way?

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This is an interesting idea. Traditionally, Motorola's antennas are purpose built to 37 Ω and due to some experiments they performed back in the late 1960's early 1970's have generally had no design alternative that worked as well in a portable environment as said 37 Ω match.

The saber is still considered one of the best performing portable radios Motorola ever manufactured. It almost makes me wonder if their antenna is a slightly modified end-fed design.


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RFI-EMI-GUY

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This is an interesting idea. Traditionally, Motorola's antennas are purpose built to 37 Ω and due to some experiments they performed back in the late 1960's early 1970's have generally had no design alternative that worked as well in a portable environment as said 37 Ω match.

The saber is still considered one of the best performing portable radios Motorola ever manufactured. It almost makes me wonder if their antenna is a slightly modified end-fed design.


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That's good to know about the 37 ohm. The HT220 series required a special matching network jig to test the radio back at 50 ohms. Wish I had known they carried that forward, I would have held onto those jigs. The later model radios all had some sort of 50 ohm port for PSM or testing.

I have this Comet BNC-24 that is a "dual band" antenna, 1/4 wave at 2 meters and 5/8 at 70cm. It gets mixed reviews. I might cobble an MX 1/4 - 24 mount on it and trim it back for GMRS to see how it goes.

The trick is, how to test the impedance. I wish I had a 12M spec for testing Saber/MX type antennas. A long time ago, I got into a discussion with the vendor of the Helical antennas because NPD had substituted -K25 antennas for the original -K08 antennas. The -K08 being NLA.

In the GMRS band, the new antenna had awful field strength and field sensitivity compared side by side with the -K08. The vendor assured me that they were tested and tuned per Motorola specs at "408 MHz", I didn't want to argue with him but thought it odd that a supposed 450-470 MHZ antenna would be tuned at 408 MHZ. I did some more testing later and found that they actually performed better in the Ham band. Also some references claim they were now 440 to 470 MHZ antennas. I never did find an answer. Mostly I am using the 1/4 wave whips now.

I agree about the Saber. I am refurbishing some Systems Sabers right now for Part 97 and for GMRS use as they are certified for Part 95. Since these were all born range 1 govt band, I am plugging in range 2 RF modules from analog donors. I have my test bench set up to do all the required tuning including the deviation balance. I have done 2 so far, and in double checking, it seems they are correct. Got 1 more to do today. Next week I start 6 more.

It is sort of an odd obsession to keep these going, but now with Lithium Ion batteries they are lighter and run forever. Also the batteries don't self discharge.



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It is sort of an odd obsession to keep these going, but now with Lithium Ion batteries they are lighter and run forever. Also the batteries don't self discharge.



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I've got several Astro's wearing the lithiums that I use for ranch radios...yea really nice in that aspect. I just wish the AVA was tri-chem.
 

RFI-EMI-GUY

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I've got several Astro's wearing the lithiums that I use for ranch radios...yea really nice in that aspect. I just wish the AVA was tri-chem.
The lithium ions that I am using, I repacked with Tenergy 31003 8.4V 2200 MAh protected cells. Opening the Motorola packs is a big chore. The charger I made from a Saber pocket charger housing fitted with a Microchip MCP73213 evaluation board. It charges in a few hours and the light indicates when actually charging.

The trick is that I used the original charging pins, but had to eliminate the protection diode forward drop, so I used a reed switch inside the pack and a magnet on the charging pocket to sense when the battery was to be charged. It works pretty well. I might try a shottkey diode on the next one. I suppose the commercial batteries have a MosFet switch or some sort of fancy arrangement.

I haven't tried the Cut Rate batteries yet. My reason for the repack experiment is that Saber battery support won't be around forever. But cutting open those battery packs with a Dremel tool is a PITA. I need to find someone with a small CNC router.

You could rework the AVA with the MCP73213 or similar and ditch the NIMH's entirely. I am not going back to NIMH.

I am going to buy a couple of the Chinese Li-Ions and try them out while they are still available. Those use a coaxial plug and dedicated charger.
 

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mancow

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This is an interesting idea. Traditionally, Motorola's antennas are purpose built to 37 Ω and due to some experiments they performed back in the late 1960's early 1970's have generally had no design alternative that worked as well in a portable environment as said 37 Ω match.

The saber is still considered one of the best performing portable radios Motorola ever manufactured. It almost makes me wonder if their antenna is a slightly modified end-fed design.


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Bendix Kings are the same.
 
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The lithium ions that I am using, I repacked with Tenergy 31003 8.4V 2200 MAh protected cells. Opening the Motorola packs is a big chore. The charger I made from a Saber pocket charger housing fitted with a Microchip MCP73213 evaluation board. It charges in a few hours and the light indicates when actually charging.

The trick is that I used the original charging pins, but had to eliminate the protection diode forward drop, so I used a reed switch inside the pack and a magnet on the charging pocket to sense when the battery was to be charged. It works pretty well. I might try a shottkey diode on the next one. I suppose the commercial batteries have a MosFet switch or some sort of fancy arrangement.

I haven't tried the Cut Rate batteries yet. My reason for the repack experiment is that Saber battery support won't be around forever. But cutting open those battery packs with a Dremel tool is a PITA. I need to find someone with a small CNC router.

You could rework the AVA with the MCP73213 or similar and ditch the NIMH's entirely. I am not going back to NIMH.

I am going to buy a couple of the Chinese Li-Ions and try them out while they are still available. Those use a coaxial plug and dedicated charger.
I've been using Power Products for mine. I've found the Impres chargers for the XTS portables work pretty well with charging the Power Products batteries.
 
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