Batboard

What is your favorite Syntor x9000, LB - 29-54 MHz antenna?

I've used a Hustler MO-3 and a 10m resonator.
I've been thinking about trying the co-phase approach of two 1/4 wave whips, 10m and 6m (cut to 30MHz and 47 MHz).
I thought I remembered a 96in whip with a tapped coil that made the antenna a half wave at 48 MHz, and it was also a 1/4 wave at ~30 MHz??? Although, I cant find the link no more for this)...

Any others, I've not thought of???

I used the dual antenna setup on my old Tahoe with a ball-mount whip for 10 and a Larsen NMO50 for 6. Worked great!

Here are the critical lengths for the coaxes if you want to go that route: The T can be any connector type - PL, N, BNC/TNC, whatever you have handy. The critical lengths between the T and antennas assume you're using standard RG58 cable with a .66 velocity factor - you'll have to re-calculate the lengths to adjust for velocity factor if you use anything else.

I strongly recommend tuning the antennas BEFORE you T them together, otherwise you'll end up chasing your tail.

As per 'otaku for 29 and 54 MHz but if you want 29 to 54 MHz then a smaller screwdriver type might be more suitable.

I'll add that receive using the dual-antenna setup was terrific across the entire 30-50 MHz band. I routinely heard CHP in the SE TX area when the band was open (not the case as of late, unfortunately) and had no problem scanning TN HP and MSP when I was in-state.

Regarding the dual antenna setup, same here. I used that on several Explorers before "downsizing" to a CRV. Worked great.
I used the NMO-50 and NMO-27 and their Antennex equivalents. Started using the Antennex because they did not break as easily when hitting trees.
But I found that I RARELY use 10, so just have one mount on the car for LB, and just change antennas when I hear activity on 10.

Hi all,

Thanks for the ideas. Has anyone seen the antennex 96 whip that covered both bands?

I appreciate the coax cut lengths. Thats what I was assuming, 1/4-wave phase reversals on opposite bands (an open at the Tee), minus Vf.

The screwdriver antenna for 25-54 MHz is an idea. The down side is, its not tuned to the current frequency your on, till its re-tuned. Same with using an auto antenna tuner.
I was thinking of a custom semi-auto tuner, where the, Syntor's AUX (VIP?) is programmed to mode banks by bands of frequencies, say every 5 MHz (bank of L/C relay selected).

Well the classic here is the AS-1729/VRC antenna which coves 30 - 76 MHz. See:

http://www.prc68.com/I/AS1729.shtml

This is essentially a sleeve diploe with the matching network in the base to cover the range in 10 ranges. The full original kit is impossibly heavy for most vehicles except perhaps large SUV or pickups. However the idea is not silly as you can get the switched bases fairly easily in bad condition and strip out the matching section guts to build your own tuner. The whips are very solid and can be often purchased on eBay or if you're good with fiberglass you can make your own.

Well I just need 29-29.7, and 47-54 MHz.

Years ago Motorola came out with a bulletin on just how to do this dual antenna installation with the T coax connector. In many police and fire vehicles that had wide split operation, like 33 and 46 MHz. the dual antenna system worked very well.

The Syntor X9000 low band radio was a work horse that is probably the best designed radio that Motorola has ever come out with. How many other radios over the years will do what this radio will do?

I use several of these radios. One in my truck and a couple in the workshop. Even have them on the VHF and UHF band. But the UHF versions of these radios has not been built in large quantities. Most of them have ended up in the New York city cab service. I tried to buy a couple UHF radios several years back when the narrow banding mandate just went into effect. But the radio shop that was selling them didn't care the cab services were buying them and using them in wide band service. Plus he wanted some blood money for the radios.

the T connector works well. If you go with a 1/4 ball mount. you could just change the whips as needed as well

My message I was writing dissapered?
I'll assume it got sent.
I was last writing that I will sub the 6m whip for a MO-3. Its thicker, so it should have more BW. We'll see.

Apparently my message was lost...
I have a loaded 10m fiberglass whip that has 1MHz of BW that I'll tune to 29.5MHz. I assume that a loaded whip is OK as 1/4-wave. The antennas are on a comm trailer mounted up high (so the 96in whip is bit too much).

On another subject. I was helping out a HAM (also with a Syntor X9000). The 6m NMO antenna was damaged. So I made a full sized whip using a NMO to 3/8th-24 adapter(it has 1/2in exposed), 3in long spring (RSS-2) and a 53.5in long whip and stud (57in total). I calculated the residence 49 MHz (234/f).
The problem is the actual residence is 57 MHz. I removed the spring, This had little effect. I sub out the NMO adapter, to using a straight 3/8th-24 mount, this too had little effect.

I have done this before* and it worked grate. Anyone seen this before?

* Maxrad part that had a spring loaded center pin, unkn pitch thread a spring (2.5in) and (52in) whip (54in). Resonated around 52MHz.

Syntor9k - you are still new enough that your posts need to be approved before they actually show up.

RE the Lost message. My mouse has two little buttons on its side. Its a right hand only mouse. And my right wrist was bothering me, so I switched to my left hand. The little buttons are real easy to touch when using my left hand. One button is forward the other is back. I just fingered this out...

motorola_otaku wrote:I used the dual antenna setup on my old Tahoe with a ball-mount whip for 10 and a Larsen NMO50 for 6. Worked great!

Here are the critical lengths for the coaxes if you want to go that route:

Code: Select all

105'' from 52 MHz antenna to tee
46'' from 29 MHz antenna to tee
If additional distance is needed, add 37'' to cable between 29 MHz antenna and tee
Tee to radio cable can be any length of any 50-ohm cable

The T can be any connector type - PL, N, BNC/TNC, whatever you have handy. The critical lengths between the T and antennas assume you're using standard RG58 cable with a .66 velocity factor - you'll have to re-calculate the lengths to adjust for velocity factor if you use anything else.

I strongly recommend tuning the antennas BEFORE you T them together, otherwise you'll end up chasing your tail.

I stared looking at the math and it appears that the length does not calculate. I assumed this was a 1/4 stub x 0.66. Were an I errorring?

syntor9k wrote:

motorola_otaku wrote:I used the dual antenna setup on my old Tahoe with a ball-mount whip for 10 and a Larsen NMO50 for 6. Worked great!

Here are the critical lengths for the coaxes if you want to go that route:

Code: Select all

105'' from 52 MHz antenna to tee
46'' from 29 MHz antenna to tee
If additional distance is needed, add 37'' to cable between 29 MHz antenna and tee
Tee to radio cable can be any length of any 50-ohm cable

The T can be any connector type - PL, N, BNC/TNC, whatever you have handy. The critical lengths between the T and antennas assume you're using standard RG58 cable with a .66 velocity factor - you'll have to re-calculate the lengths to adjust for velocity factor if you use anything else.

I strongly recommend tuning the antennas BEFORE you T them together, otherwise you'll end up chasing your tail.

I stared looking at the math and it appears that the length does not calculate. I assumed this was a 1/4 stub x 0.66. Were an I errorring?

No, these are not exact 1/4-wave lengths. I took the measurements from the official Motorola chart (which you can find on Repeater Builder) and extrapolated the lengths from that - up from 50 MHz and down from 30 MHz. It works, I assure you.

They lengths would only be a quarter wave if the impedance at the base of the antenna that was not in use was 0R+j0 so that at the T will be transformed to an open circuit. Since the antennas are not shorts at each other's frequency the cable lengths have to be adjusted to transform the impedance appropriately.

OK I see. I think, that the currently not used antenna is either a short or an open. The 10m 1/4W on 6m is a 1/2W (approx) for 6m, this is 500-1000 Ohms. The 6m antenna is 1/8th wave, this is more like a short i suspect. These are my best guesses...

Any way, I cant wait to see how it works and over what frequency ranges...

Bad news...
It did not work. The coax is 58A/U, clear not foam center conductor coax. 105in on the 6m whip, and 46in on the 10m antenna.
Also, I found that the PLL (I'm assuming) is not locking, no 29-29.68 MHz output. This was a SWR test with radios transmitter...
I tested it on 48 and 52.525 MHz ~2.5-3.5 SWR. When the non-T'd antenna was 1.2 and 1.9 SWR. 29.5 MHz was tuned via a MFJ-269 and was 1.5 SWR.

Do to a lack of response. I'll assume that the two coaxes are different. I'll go find some RG-58U (both are 0.66Vf), and start over.

If your using a spring under a whip, you need to make sure the braid inside the spring is still functional. This braid goes bad over time and will cause you untold grief trying to get an antenna to tune. Up in the northern states where salt is used on the roads, these springs will only last a couple of years if your lucky.

The best way of checking the braid inside the spring is to bend the spring over at close to a 90 degree angle and take a flashlight to examine the braid. If it's frayed, it would be a good idea to replace the spring. Otherwise you will be chasing your tail, trying to get the antenna tuned to where you want it.

Found this bad boy problem many years ago and vowed to never again to get bit by the problem. So passing along this simple tip to anyone using a spring under their mobile whip antenna.

Jim

The 10m antenna is brand new. The 6m antenna is recycled and spring is rusty. But the SWR is normal on it. I'll check it...
BTW. I went shopping for smaller spring and found that its become common that do to cost cutting, the braid has been eliminated (unconfirmed).

I used the dual antenna arrangement for years with Spectrum antennas on 29.6 and 52.5 with no issues. The coax lengths are great for a car with a full sized trunk and the drawers mounted on the right side.

I redid the set up with new belden RG-58U coax. Same out come. No good. I plan on adding few different patch cables of different lengths and see what happens...

George wrote:I used the dual antenna arrangement for years with Spectrum antennas on 29.6 and 52.5 with no issues. The coax lengths are great for a car with a full sized trunk and the drawers mounted on the right side.

I assume your antennas ware loaded antennas. Mine are 1/4-wave whips on ball mounts...

Good news. I got the antenna system working. The 47-52 MHz side needs slight tweaking, otherwise works fine (it shifted down in frequency, and now 52.525 MHz SWR is close to 3.0, it was around 2.0).

Bad news. I have no positive idea what exactly changed. I found that the spring was loose on the mount (it wasn't loose when I checked the internal braid. The SWR was OK then too). There was another vehicle with low band, parked within 10Ft (I didn't have the keys for), got moved. And My MFJ analyzer needed to get repaired/ calibrated was returned (I rechecked it with a SWR/ WATT meter, too).

Thanks all, for the help...