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HT750/HT1250 Low band antenna - red color code??

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g8tzl2004
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HT750/HT1250 Low band antenna - red color code??

Postby g8tzl2004 » Fri Jun 07, 2019 2:37 pm

I have a helical antenna with a red color code on the screw thread.

It is about 7.5 inches long and 0.5 inches wide and does not taper

There is no "Motorola" logo.

I looked up a Motorola cutting chart and it indicated that the antenna had been cut for around 47 MHz.

But I'm not 100% certain that it is for a Motorola HT750/HT1250..it definitely fits my low band HT750 (which came without an antenna) but it could be made for another manufacturer or be for a different band...such as the European 68 - 88 MHz band?

Any thoughts?

chrismoll12
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Re: HT750/HT1250 Low band antenna - red color code??

Postby chrismoll12 » Sun Jun 09, 2019 7:32 pm

Moto did have other low band antennas besides uncut 6064. I'd figure moto wouldnt pass on branding an item so I'd assume aftermarket and theres still a few companies making aftermarket antennas for old motos, laird, smiley antenna makes lots of nice ducks with any connector of your choice, etc

NAB6061 30-36 GREEN
NAB6062 36-42 BLUE
NAB6063 42-50 RED
NAB6064 Uncut 12"

g8tzl2004
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Re: HT750/HT1250 Low band antenna - red color code??

Postby g8tzl2004 » Tue Jun 11, 2019 6:10 am

OK thanks.

So the antenna could be an aftermarket NAB6063 with the red color code...which fits with Motorola cutting chart giving 47 MHz.

When you buy a NAB6063 42 - 50 MHZ, can you use this antenna to TX/RX anywhere between 42 and 50 MHz without cutting the antenna to a specific spot frequency....so you get an 8 MHz spread at an acceptable SWR? I guess a 42 to 50 MHz antenna is actually cut for 46 MHz ie the middle of the range?

Karl NVW
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Re: HT750/HT1250 Low band antenna - red color code??

Postby Karl NVW » Tue Jun 11, 2019 7:16 pm

If you follow the alignment instructions in the radio manual, tuning of the TX output stage will take the antenna impedance into account on the working frequencies.
Karl - WA8NVW AFA5VB
SHARES + NCS

com501
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What radios do you own?: Over 50 - All Motorola

Re: HT750/HT1250 Low band antenna - red color code??

Postby com501 » Wed Jun 12, 2019 11:04 am

You should trim the antenna according to the cutting chart. The antenna for low band is only good for a small (1.5mHz) range, and you cannot 'tune' a Waris Series HT, other than in tuner to set the rated power output.

g8tzl2004
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Re: HT750/HT1250 Low band antenna - red color code??

Postby g8tzl2004 » Wed Jun 12, 2019 1:48 pm

You wonder why Motorola makes 4 different versions of the low band antenna when they probably all need to be cut!!!...although I guess its cheaper to buy a 42 - 50 MHz vs 30 - 36 MHz antenna as there is less "wire" and "rubber" :)

I guess the uncut version is ideal for 29.6 MHz!!

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NSPD
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Re: HT750/HT1250 Low band antenna - red color code??

Postby NSPD » Sat Jun 15, 2019 11:20 am

The antenna comes with a cutting chart when you order one. FYI, it needs to be cut to different lengths for the same frequency depending on whether you will be holding the radio in your hand or using it on your belt with a speaker mic.
Jake

g8tzl2004
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Re: HT750/HT1250 Low band antenna - red color code??

Postby g8tzl2004 » Sat Jun 15, 2019 4:02 pm

Interesting. The speaker mic cord must be acting as a ground plane and affecting the SWR!!

A 29.6 MHz 1ft helical with no ground plane must be very inefficient... I wonder how many -dB's compared to a dipole!!

I have noticed a massive improvement in RX on higher bands such as 6m when you simply rest a HT on a metal vehicle roof...which acts as a ground plane and the HT must get some inductive coupling!!

Karl NVW
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Re: HT750/HT1250 Low band antenna - red color code??

Postby Karl NVW » Mon Jun 17, 2019 10:33 am

Unofficially, engineering field strength tests on the antenna range were in the area of 18 to 24 dB loss relative to isotropic. And it obviously got worse if the user "stored" the speaker-mic coil cord by wrapping it around the antenna.
Karl - WA8NVW AFA5VB
SHARES + NCS

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NSPD
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Re: HT750/HT1250 Low band antenna - red color code??

Postby NSPD » Wed Jun 19, 2019 5:00 am

I wish there was a way to adapt one of the Harris or Thales 30-108 whips to these but I think that may be a difficult thing to accomplish with the way the radio is designed.
Jake

g8tzl2004
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Re: HT750/HT1250 Low band antenna - red color code??

Postby g8tzl2004 » Wed Jun 19, 2019 8:21 am

Assuming a mid-range loss of 21dB relative to an isotropic, I think this suggests that 6W from a low band HT750 is effectively 30mW given the losses using the helical!!!....and an isotropic is 2.15dB greater than a dipole...so relative to a dipole its equivalent to around 20mW!!

So 20mW using a low band dipole gets the same range as 6W from a HT750 using a helical !!

6W=36dBm; 0.03W=15dBm (difference -21dBm); 0.02W=13dBm


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